贷款利息计算器

sfc4621

根据不同的还款方式计算出合适的利息还款方式

[Python] 纯文本查看 复制代码

import tkinter as tk
from tkinter import ttk, messagebox
import math

class LoanCalculator:
    def __init__(self, root):
        self.root = root
        self.root.title("贷款利息计算器")
        self.root.geometry("580x600")
        self.root.resizable(False, False)
        
        # 初始化变量
        self.loan_amount = tk.StringVar()  # 贷款金额
        self.annual_rate = tk.StringVar()  # 年利率(%)
        self.loan_years = tk.StringVar()   # 贷款年限
        self.result_var = tk.StringVar()   # 计算结果
        self.recommend_var = tk.StringVar()# 推荐方案
        
        # 创建界面
        self.create_widgets()
    
    def create_widgets(self):
        # 标题
        title_label = ttk.Label(
            self.root, 
            text="贷款利息计算器", 
            font=("微软雅黑", 16, "bold")
        )
        title_label.pack(pady=10)
        
        # 输入框架
        input_frame = ttk.LabelFrame(self.root, text="贷款信息")
        input_frame.pack(padx=20, pady=10, fill="x")
        
        # 贷款金额
        ttk.Label(input_frame, text="贷款金额(元):").grid(row=0, column=0, padx=10, pady=8, sticky="w")
        amount_entry = ttk.Entry(input_frame, textvariable=self.loan_amount, width=30)
        amount_entry.grid(row=0, column=1, padx=10, pady=8)
        
        # 年利率
        ttk.Label(input_frame, text="年利率(%):").grid(row=1, column=0, padx=10, pady=8, sticky="w")
        rate_entry = ttk.Entry(input_frame, textvariable=self.annual_rate, width=30)
        rate_entry.grid(row=1, column=1, padx=10, pady=8)
        
        # 贷款年限
        ttk.Label(input_frame, text="贷款年限(年):").grid(row=2, column=0, padx=10, pady=8, sticky="w")
        years_entry = ttk.Entry(input_frame, textvariable=self.loan_years, width=30)
        years_entry.grid(row=2, column=1, padx=10, pady=8)
        
        # 计算按钮
        calc_btn = ttk.Button(
            self.root, 
            text="计算并推荐最优方案", 
            command=self.calculate_loan
        )
        calc_btn.pack(pady=10)
        
        # 结果框架
        result_frame = ttk.LabelFrame(self.root, text="计算结果")
        result_frame.pack(padx=20, pady=5, fill="both", expand=True)
        
        # 结果文本框
        self.result_text = tk.Text(result_frame, font=("微软雅黑", 10), wrap=tk.WORD)
        scrollbar = ttk.Scrollbar(result_frame, orient="vertical", command=self.result_text.yview)
        self.result_text.configure(yscrollcommand=scrollbar.set)
        
        self.result_text.pack(side="left", fill="both", expand=True, padx=(0, 5), pady=5)
        scrollbar.pack(side="right", fill="y", pady=5)
        
        # 推荐方案标签
        recommend_label = ttk.Label(
            self.root, 
            textvariable=self.recommend_var,
            font=("微软雅黑", 11, "bold"),
            foreground="#d63031"
        )
        recommend_label.pack(pady=8)
    
    def validate_inputs(self):
        """验证输入是否合法"""
        try:
            amount = float(self.loan_amount.get())
            rate = float(self.annual_rate.get())
            years = int(self.loan_years.get())
            
            if amount <= 0:
                messagebox.showerror("错误", "贷款金额必须大于0！")
                return None
            if rate <= 0 or rate > 100:
                messagebox.showerror("错误", "年利率必须在0-100之间！")
                return None
            if years <= 0 or years > 50:
                messagebox.showerror("错误", "贷款年限必须在1-50之间！")
                return None
            
            return amount, rate, years
        except ValueError:
            messagebox.showerror("错误", "请输入有效的数字！")
            return None
    
    def calculate_equal_principal_interest(self, principal, annual_rate, years):
        """
        计算等额本息还款方式
        公式：
        月利率 = 年利率 / 12 / 100
        月供 = 本金 × 月利率 × (1 + 月利率)^还款月数 / [(1 + 月利率)^还款月数 - 1]
        总利息 = 月供 × 还款月数 - 本金
        """
        monthly_rate = annual_rate / 12 / 100
        months = years * 12
        
        if monthly_rate == 0:
            monthly_payment = principal / months
            total_interest = 0
        else:
            monthly_payment = principal * monthly_rate * math.pow(1 + monthly_rate, months) / (math.pow(1 + monthly_rate, months) - 1)
            total_interest = monthly_payment * months - principal
        
        return {
            "monthly_payment": monthly_payment,
            "total_interest": total_interest,
            "total_payment": principal + total_interest
        }
    
    def calculate_equal_principal(self, principal, annual_rate, years):
        """
        计算等额本金还款方式
        公式：
        月利率 = 年利率 / 12 / 100
        每月应还本金 = 本金 / 还款月数
        每月应还利息 = 剩余本金 × 月利率
        总利息 = (还款月数 + 1) × 本金 × 月利率 / 2
        """
        monthly_rate = annual_rate / 12 / 100
        months = years * 12
        monthly_principal = principal / months
        
        # 计算总利息
        total_interest = (months + 1) * principal * monthly_rate / 2
        # 首月还款额
        first_month_payment = monthly_principal + principal * monthly_rate
        # 每月递减金额
        monthly_decrease = monthly_principal * monthly_rate
        
        return {
            "first_month_payment": first_month_payment,
            "monthly_decrease": monthly_decrease,
            "total_interest": total_interest,
            "total_payment": principal + total_interest
        }
    
    def calculate_interest_first_principal_last(self, principal, annual_rate, years):
        """
        计算到期还本、按期还息（先息后本）还款方式
        公式：
        月利率 = 年利率 / 12 / 100
        每月还息 = 本金 × 月利率
        到期还本 = 本金
        总利息 = 本金 × 年利率 × 年限
        """
        monthly_rate = annual_rate / 12 / 100
        # 每月还息金额
        monthly_interest = principal * monthly_rate
        # 总利息
        total_interest = principal * annual_rate * years / 100
        # 总还款金额
        total_payment = principal + total_interest
        
        return {
            "monthly_interest": monthly_interest,
            "final_principal": principal,
            "total_interest": total_interest,
            "total_payment": total_payment
        }
    
    def calculate_loan(self):
        """主计算函数"""
        # 清空结果
        self.result_text.delete(1.0, tk.END)
        self.recommend_var.set("")
        
        # 验证输入
        inputs = self.validate_inputs()
        if not inputs:
            return
        
        principal, annual_rate, years = inputs
        months = years * 12
        
        # 计算三种还款方式
        eqi_pi = self.calculate_equal_principal_interest(principal, annual_rate, years)  # 等额本息
        eqi_p = self.calculate_equal_principal(principal, annual_rate, years)            # 等额本金
        interest_first = self.calculate_interest_first_principal_last(principal, annual_rate, years)  # 先息后本
        
        # 构建结果文本
        result_text = f"""
【贷款基本信息】
贷款金额：{principal:,.2f} 元
年利率：{annual_rate:.2f} %
贷款年限：{years} 年（{months} 个月）

【等额本息还款方案】
每月还款额：{eqi_pi['monthly_payment']:,.2f} 元
总还款金额：{eqi_pi['total_payment']:,.2f} 元
总支付利息：{eqi_pi['total_interest']:,.2f} 元

【等额本金还款方案】
首月还款额：{eqi_p['first_month_payment']:,.2f} 元
每月递减金额：{eqi_p['monthly_decrease']:,.4f} 元
总还款金额：{eqi_p['total_payment']:,.2f} 元
总支付利息：{eqi_p['total_interest']:,.2f} 元

【到期还本、按期还息（先息后本）方案】
每月还息金额：{interest_first['monthly_interest']:,.2f} 元
到期还本金额：{interest_first['final_principal']:,.2f} 元
总还款金额：{interest_first['total_payment']:,.2f} 元
总支付利息：{interest_first['total_interest']:,.2f} 元

【三种方案利息对比】
等额本息利息：{eqi_pi['total_interest']:,.2f} 元
等额本金利息：{eqi_p['total_interest']:,.2f} 元
先息后本利息：{interest_first['total_interest']:,.2f} 元
        """
        
        # 插入结果
        self.result_text.insert(tk.END, result_text)
        self.result_text.see(tk.END)
        
        # 找出利息最低的方案
        interest_dict = {
            "等额本金": eqi_p['total_interest'],
            "等额本息": eqi_pi['total_interest'],
            "到期还本、按期还息": interest_first['total_interest']
        }
        # 按利息升序排序
        sorted_interest = sorted(interest_dict.items(), key=lambda x: x[1])
        best_plan = sorted_interest[0][0]
        best_interest = sorted_interest[0][1]
        second_interest = sorted_interest[1][1]
        interest_diff = second_interest - best_interest
        
        # 推荐最优方案
        self.recommend_var.set(f"&#9989; 推荐方案：{best_plan}（总利息最低，为 {best_interest:,.2f} 元，比第二名少付 {interest_diff:,.2f} 元）")

if __name__ == "__main__":
    root = tk.Tk()
    app = LoanCalculator(root)
    root.mainloop()

helh0275

亡屿歌 发表于 2026-3-13 23:06
找千问翻译了一份，页面图标什么的反正一股子AI味儿，凑活能看，大家可以保存试一试。

这是一个完整的单 ...

好像点击计算并推荐最优方案无效

picoyiyi

少污污 发表于 2026-3-13 19:44
再弄一个HTML版本。

臣附议！比较容易操作

FQY188

很好的工具，有房贷的朋友可以计算一下

helh0275

感谢分享，但有成品该多好

lxyi

厉害厉害

siqi47

刚好算算我的房贷。

少污污

再弄一个HTML版本。

亡屿歌

找千问翻译了一份，页面图标什么的反正一股子AI味儿，凑活能看，大家可以保存试一试。
这是一个完整的单文件 HTML 解决方案。我将 Python tkinter 的逻辑完全转换为了 JavaScript，并使用了现代化的 CSS 样式（类似 Bootstrap 的风格），使其在浏览器中美观且易于使用。
第二版，修改了部分代码，确保功能可用。
使用方法：

• 新建一个文本文件，命名为 loan_calculator.html。
• 将下面的代码完整复制粘贴进去。
• 保存并双击打开，即可在浏览器中使用。
  

[HTML] 纯文本查看 复制代码

<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>智能贷款计算器 | Loan Calculator</title>
    <!-- 引入优质字体 -->
    <link rel="preconnect" href="https://fonts.googleapis.com">
    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
    <link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&family=JetBrains+Mono:wght@400;500&display=swap" rel="stylesheet">
    
    <style>
        :root {
            /* 配色系统 */
            --primary: #4f46e5;
            --primary-hover: #4338ca;
            --secondary: #ec4899;
            --accent: #06b6d4;
            --bg-gradient: linear-gradient(135deg, #f0f4ff 0%, #eef2f3 100%);
            --card-bg: rgba(255, 255, 255, 0.95);
            --text-main: #1e293b;
            --text-sub: #64748b;
            --border-color: #e2e8f0;
            --success-bg: #dcfce7;
            --success-text: #166534;
            --shadow-sm: 0 4px 6px -1px rgba(0, 0, 0, 0.05), 0 2px 4px -1px rgba(0, 0, 0, 0.03);
            --shadow-lg: 0 20px 25px -5px rgba(0, 0, 0, 0.05), 0 10px 10px -5px rgba(0, 0, 0, 0.02);
            --radius-xl: 24px;
            --radius-md: 12px;
        }

        * {
            box-sizing: border-box;
            margin: 0;
            padding: 0;
            outline: none;
        }

        body {
            font-family: 'Inter', system-ui, -apple-system, sans-serif;
            background: var(--bg-gradient);
            background-attachment: fixed;
            min-height: 100vh;
            display: flex;
            justify-content: center;
            align-items: center;
            padding: 20px;
            color: var(--text-main);
            line-height: 1.6;
        }

        /* 背景装饰球 */
        .bg-blob {
            position: fixed;
            border-radius: 50%;
            filter: blur(80px);
            z-index: -1;
            opacity: 0.6;
            animation: float 10s infinite ease-in-out;
        }
        .blob-1 { top: -10%; left: -10%; width: 500px; height: 500px; background: #c7d2fe; }
        .blob-2 { bottom: -10%; right: -10%; width: 400px; height: 400px; background: #fbcfe8; animation-delay: -5s; }

        @keyframes float {
            0%, 100% { transform: translate(0, 0); }
            50% { transform: translate(20px, 30px); }
        }

        .container {
            width: 100%;
            max-width: 800px;
            background: var(--card-bg);
            backdrop-filter: blur(20px);
            -webkit-backdrop-filter: blur(20px);
            border-radius: var(--radius-xl);
            box-shadow: var(--shadow-lg);
            border: 1px solid rgba(255, 255, 255, 0.8);
            overflow: hidden;
            transition: transform 0.3s ease;
        }

        header {
            padding: 30px 40px 20px;
            text-align: center;
            border-bottom: 1px solid var(--border-color);
            background: linear-gradient(to bottom, rgba(255,255,255,0.5), transparent);
        }

        h1 {
            font-size: 1.8rem;
            font-weight: 800;
            color: var(--text-main);
            margin-bottom: 8px;
            letter-spacing: -0.5px;
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 12px;
        }

        h1 span {
            background: linear-gradient(135deg, var(--primary), var(--secondary));
            -webkit-background-clip: text;
            -webkit-text-fill-color: transparent;
        }

        .subtitle {
            color: var(--text-sub);
            font-size: 0.95rem;
            font-weight: 500;
        }

        .content {
            padding: 30px 40px 40px;
        }

        /* 输入区域网格 */
        .input-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
            gap: 24px;
            margin-bottom: 30px;
        }

        .input-group {
            position: relative;
        }

        .input-group label {
            display: block;
            font-size: 0.85rem;
            font-weight: 600;
            color: var(--text-sub);
            margin-bottom: 8px;
            padding-left: 4px;
        }

        .input-wrapper {
            position: relative;
            display: flex;
            align-items: center;
        }

        .input-icon {
            position: absolute;
            left: 16px;
            color: var(--text-sub);
            font-size: 1.1rem;
            pointer-events: none;
            transition: color 0.2s;
        }

        input[type="number"] {
            width: 100%;
            padding: 14px 16px 14px 44px;
            font-family: 'JetBrains Mono', monospace;
            font-size: 1rem;
            font-weight: 500;
            color: var(--text-main);
            background: #f8fafc;
            border: 2px solid transparent;
            border-radius: var(--radius-md);
            transition: all 0.2s ease;
            box-shadow: inset 0 2px 4px rgba(0,0,0,0.02);
        }

        input[type="number"]:focus {
            background: #fff;
            border-color: var(--primary);
            box-shadow: 0 0 0 4px rgba(79, 70, 229, 0.1);
        }

        input[type="number"]:focus + .input-icon,
        .input-wrapper:focus-within .input-icon {
            color: var(--primary);
        }

        /* 按钮样式 */
        .btn-calc {
            width: 100%;
            padding: 16px;
            border: none;
            border-radius: var(--radius-md);
            background: linear-gradient(135deg, var(--primary) 0%, var(--primary-hover) 100%);
            color: white;
            font-size: 1.1rem;
            font-weight: 700;
            cursor: pointer;
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 10px;
            box-shadow: 0 10px 20px -5px rgba(79, 70, 229, 0.4);
            transition: all 0.2s ease;
            position: relative;
            overflow: hidden;
        }

        .btn-calc:hover {
            transform: translateY(-2px);
            box-shadow: 0 15px 25px -5px rgba(79, 70, 229, 0.5);
        }

        .btn-calc:active {
            transform: translateY(0);
            box-shadow: 0 5px 10px -5px rgba(79, 70, 229, 0.4);
        }

        .btn-calc::after {
            content: '';
            position: absolute;
            top: 0; left: 0; right: 0; bottom: 0;
            background: linear-gradient(rgba(255,255,255,0.2), transparent);
            opacity: 0;
            transition: opacity 0.2s;
        }
        .btn-calc:hover::after { opacity: 1; }

        /* 结果展示区 */
        .results-container {
            margin-top: 35px;
            display: grid;
            grid-template-columns: 1fr;
            gap: 20px;
            opacity: 0;
            transform: translateY(10px);
            transition: all 0.4s ease;
        }

        .results-container.show {
            opacity: 1;
            transform: translateY(0);
        }

        .result-card {
            background: #fff;
            border: 1px solid var(--border-color);
            border-radius: var(--radius-md);
            padding: 20px;
            box-shadow: var(--shadow-sm);
        }

        .result-header {
            font-size: 1.1rem;
            font-weight: 700;
            color: var(--text-main);
            margin-bottom: 15px;
            padding-bottom: 10px;
            border-bottom: 2px dashed var(--border-color);
            display: flex;
            align-items: center;
            gap: 8px;
        }

        .result-grid {
            display: grid;
            grid-template-columns: repeat(2, 1fr);
            gap: 15px;
        }

        .data-item {
            display: flex;
            flex-direction: column;
        }

        .data-label {
            font-size: 0.8rem;
            color: var(--text-sub);
            margin-bottom: 4px;
        }

        .data-value {
            font-family: 'JetBrains Mono', monospace;
            font-size: 1.05rem;
            font-weight: 600;
            color: var(--text-main);
        }

        .data-value.highlight {
            color: var(--primary);
            font-size: 1.2rem;
        }

        /* 推荐徽章 */
        .recommend-badge {
            background: var(--success-bg);
            color: var(--success-text);
            padding: 16px 20px;
            border-radius: var(--radius-md);
            border: 1px solid #bbf7d0;
            display: flex;
            align-items: center;
            gap: 12px;
            font-weight: 600;
            margin-top: 20px;
            animation: pulse 2s infinite;
        }

        @keyframes pulse {
            0% { box-shadow: 0 0 0 0 rgba(22, 101, 52, 0.2); }
            70% { box-shadow: 0 0 0 10px rgba(22, 101, 52, 0); }
            100% { box-shadow: 0 0 0 0 rgba(22, 101, 52, 0); }
        }

        .badge-icon {
            font-size: 1.4rem;
        }

        /* 响应式调整 */
        @media (max-width: 600px) {
            .content { padding: 20px; }
            header { padding: 20px 20px 15px; }
            h1 { font-size: 1.5rem; }
            .result-grid { grid-template-columns: 1fr; }
            .input-grid { grid-template-columns: 1fr; }
        }

        /* 滚动条美化 */
        ::-webkit-scrollbar { width: 8px; }
        ::-webkit-scrollbar-track { background: #f1f5f9; border-radius: 4px; }
        ::-webkit-scrollbar-thumb { background: #cbd5e1; border-radius: 4px; }
        ::-webkit-scrollbar-thumb:hover { background: #94a3b8; }
    </style>
</head>
<body>

    <!-- 背景装饰 -->
    <div class="bg-blob blob-1"></div>
    <div class="bg-blob blob-2"></div>

    <div class="container">
        <header>
            <h1><span>&#128176;</span> 智能贷款计算器</h1>
            <div class="subtitle">等额本息 · 等额本金 · 先息后本 · 一键对比最优方案</div>
        </header>

        <div class="content">
            <!-- 输入区域 -->
            <div class="input-grid">
                <div class="input-group">
                    <label for="amount">贷款金额 (元)</label>
                    <div class="input-wrapper">
                        <input type="number" id="amount" value="100000" step="1000" min="1">
                        <span class="input-icon">&#127974;</span>
                    </div>
                </div>
                <div class="input-group">
                    <label for="rate">年利率 (%)</label>
                    <div class="input-wrapper">
                        <input type="number" id="rate" value="4.5" step="0.1" min="0.01" max="100">
                        <span class="input-icon">&#128200;</span>
                    </div>
                </div>
                <div class="input-group">
                    <label for="years">贷款年限 (年)</label>
                    <div class="input-wrapper">
                        <input type="number" id="years" value="20" step="1" min="1" max="50">
                        <span class="input-icon">&#128197;</span>
                    </div>
                </div>
            </div>

            <button class="btn-calc" id="calculateBtn">
                <span>&#9889; 开始计算并推荐</span>
                <svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><polyline points="9 18 15 12 9 6"></polyline></svg>
            </button>

            <!-- 结果区域 -->
            <div class="results-container" id="resultsArea">
                
                <!-- 推荐徽章 -->
                <div class="recommend-badge" id="recommendDisplay" style="display: none;">
                    <span class="badge-icon">&#127942;</span>
                    <span id="recommendText"></span>
                </div>

                <div class="result-grid">
                    <!-- 等额本息 -->
                    <div class="result-card">
                        <div class="result-header">
                            <span>&#128260;</span> 等额本息
                        </div>
                        <div class="data-item" style="margin-bottom: 15px;">
                            <span class="data-label">每月还款</span>
                            <span class="data-value highlight" id="eqpi-monthly">-</span>
                        </div>
                        <div class="result-grid" style="gap: 10px;">
                            <div class="data-item">
                                <span class="data-label">总利息</span>
                                <span class="data-value" id="eqpi-interest">-</span>
                            </div>
                            <div class="data-item">
                                <span class="data-label">总还款</span>
                                <span class="data-value" id="eqpi-total">-</span>
                            </div>
                        </div>
                    </div>

                    <!-- 等额本金 -->
                    <div class="result-card">
                        <div class="result-header">
                            <span>&#128201;</span> 等额本金
                        </div>
                        <div class="data-item" style="margin-bottom: 15px;">
                            <span class="data-label">首月还款</span>
                            <span class="data-value highlight" id="eqp-first">-</span>
                        </div>
                        <div class="result-grid" style="gap: 10px;">
                            <div class="data-item">
                                <span class="data-label">每月递减</span>
                                <span class="data-value" id="eqp-decrease">-</span>
                            </div>
                            <div class="data-item">
                                <span class="data-label">总利息</span>
                                <span class="data-value" id="eqp-interest">-</span>
                            </div>
                        </div>
                    </div>

                    <!-- 先息后本 -->
                    <div class="result-card">
                        <div class="result-header">
                            <span>&#128184;</span> 先息后本
                        </div>
                        <div class="data-item" style="margin-bottom: 15px;">
                            <span class="data-label">每月只还息</span>
                            <span class="data-value highlight" id="if-monthly">-</span>
                        </div>
                        <div class="result-grid" style="gap: 10px;">
                            <div class="data-item">
                                <span class="data-label">到期还本</span>
                                <span class="data-value" id="if-principal">-</span>
                            </div>
                            <div class="data-item">
                                <span class="data-label">总利息</span>
                                <span class="data-value" id="if-interest">-</span>
                            </div>
                        </div>
                    </div>
                </div>

                <div style="text-align: center; margin-top: 20px; font-size: 0.85rem; color: var(--text-sub);">
                    &#128161; 数据仅供参考，具体以银行合同为准 · 每月递减精确到小数点后四位
                </div>
            </div>
        </div>
    </div>

    <script>
        (function() {
            const amountInput = document.getElementById('amount');
            const rateInput = document.getElementById('rate');
            const yearsInput = document.getElementById('years');
            const calcBtn = document.getElementById('calculateBtn');
            const resultsArea = document.getElementById('resultsArea');
            const recommendDisplay = document.getElementById('recommendDisplay');
            const recommendText = document.getElementById('recommendText');

            // 格式化货币
            const fmtMoney = (num) => num.toFixed(2).replace(/\B(?=(\d{3})+(?!\d))/g, ',');
            const fmtNum = (num, digits = 2) => Number(num).toFixed(digits);

            function validateInputs() {
                let amount = parseFloat(amountInput.value);
                let rate = parseFloat(rateInput.value);
                let years = parseInt(yearsInput.value, 10);

                if (isNaN(amount) || amount <= 0) { alert('&#10060; 贷款金额必须大于 0！'); return null; }
                if (isNaN(rate) || rate <= 0 || rate > 100) { alert('&#10060; 年利率必须在 0~100 之间！'); return null; }
                if (isNaN(years) || years <= 0 || years > 50) { alert('&#10060; 贷款年限必须在 1~50 年之间！'); return null; }
                return { amount, rate, years };
            }

            function calcEqualPrincipalInterest(principal, annualRate, years) {
                const monthlyRate = annualRate / 12 / 100;
                const months = years * 12;
                if (monthlyRate === 0) return { monthlyPayment: principal / months, totalInterest: 0, totalPayment: principal };
                const factor = Math.pow(1 + monthlyRate, months);
                const monthlyPayment = principal * monthlyRate * factor / (factor - 1);
                const totalInterest = monthlyPayment * months - principal;
                return { monthlyPayment, totalInterest, totalPayment: principal + totalInterest };
            }

            function calcEqualPrincipal(principal, annualRate, years) {
                const monthlyRate = annualRate / 12 / 100;
                const months = years * 12;
                const monthlyPrincipal = principal / months;
                const totalInterest = (months + 1) * principal * monthlyRate / 2;
                const firstMonthPayment = monthlyPrincipal + principal * monthlyRate;
                const monthlyDecrease = monthlyPrincipal * monthlyRate;
                return { firstMonthPayment, monthlyDecrease, totalInterest, totalPayment: principal + totalInterest };
            }

            function calcInterestFirst(principal, annualRate, years) {
                const monthlyRate = annualRate / 12 / 100;
                const monthlyInterest = principal * monthlyRate;
                const totalInterest = principal * annualRate * years / 100;
                return { monthlyInterest, finalPrincipal: principal, totalInterest, totalPayment: principal + totalInterest };
            }

            function updateUI(eqPI, eqP, interestFirst) {
                // 填充数据
                document.getElementById('eqpi-monthly').textContent = fmtMoney(eqPI.monthlyPayment) + ' 元';
                document.getElementById('eqpi-interest').textContent = fmtMoney(eqPI.totalInterest) + ' 元';
                document.getElementById('eqpi-total').textContent = fmtMoney(eqPI.totalPayment) + ' 元';

                document.getElementById('eqp-first').textContent = fmtMoney(eqP.firstMonthPayment) + ' 元';
                document.getElementById('eqp-decrease').textContent = fmtNum(eqP.monthlyDecrease, 4) + ' 元';
                document.getElementById('eqp-interest').textContent = fmtMoney(eqP.totalInterest) + ' 元';

                document.getElementById('if-monthly').textContent = fmtMoney(interestFirst.monthlyInterest) + ' 元';
                document.getElementById('if-principal').textContent = fmtMoney(interestFirst.finalPrincipal) + ' 元';
                document.getElementById('if-interest').textContent = fmtMoney(interestFirst.totalInterest) + ' 元';

                // 推荐逻辑
                const plans = [
                    { name: '等额本金', interest: eqP.totalInterest },
                    { name: '等额本息', interest: eqPI.totalInterest },
                    { name: '先息后本', interest: interestFirst.totalInterest }
                ];
                plans.sort((a, b) => a.interest - b.interest);
                const best = plans[0];
                const second = plans[1];
                const diff = second.interest - best.interest;

                recommendText.innerHTML = `最优方案：<strong>${best.name}</strong> · 总利息仅需 ${fmtMoney(best.interest)} 元 <br><span style="font-size:0.9em; opacity:0.9">比第二名的 ${second.name} 节省 ${fmtMoney(diff)} 元</span>`;
                recommendDisplay.style.display = 'flex';
                
                // 动画显示
                resultsArea.classList.add('show');
            }

            function calculate() {
                const validated = validateInputs();
                if (!validated) return;

                const { amount, rate, years } = validated;
                const eqPI = calcEqualPrincipalInterest(amount, rate, years);
                const eqP = calcEqualPrincipal(amount, rate, years);
                const interestFirst = calcInterestFirst(amount, rate, years);

                updateUI(eqPI, eqP, interestFirst);
                
                // 平滑滚动到结果区
                setTimeout(() => {
                    resultsArea.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
                }, 100);
            }

            calcBtn.addEventListener('click', calculate);
            
            [amountInput, rateInput, yearsInput].forEach(input => {
                input.addEventListener('keypress', (e) => {
                    if (e.key === 'Enter') { e.preventDefault(); calculate(); }
                });
            });

            // 初始化运行一次
            window.addEventListener('load', calculate);
        })();
    </script>
</body>
</html>

zhjm21

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