纯 Java 个人所得税计算模拟器

个税计算核心类

核心计算部分使用了 BigDecimal 来处理金额，这一点很重要。税务计算对精度比较敏感，直接用 double 容易在累加、比较和格式化时出现细小误差，所以这里在计算过程中尽量用 BigDecimal，最后再转换成展示需要的数值。

package com.tax.calculator;

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.HashMap;
import java.util.Map;

/**
 * 个人所得税计算器
 * 实现年度综合所得个税计算规则
 */
public class TaxCalculator {
    
    // 税率表（年度综合所得）
    private static final TaxBracket[] TAX_BRACKETS = {
        new TaxBracket(0, 36000, 0.03, 0),
        new TaxBracket(36000, 144000, 0.10, 2520),
        new TaxBracket(144000, 300000, 0.20, 16920),
        new TaxBracket(300000, 420000, 0.25, 31920),
        new TaxBracket(420000, 660000, 0.30, 52920),
        new TaxBracket(660000, 960000, 0.35, 85920),
        new TaxBracket(960000, Double.MAX_VALUE, 0.45, 181920)
    };
    
    // 月度专项扣除标准
    private static final Map<String, BigDecimal> SPECIAL_DEDUCTIONS = new HashMap<>();
    
    static {
        // 初始化专项扣除标准（月度）
        SPECIAL_DEDUCTIONS.put("养老", new BigDecimal("1000"));
        SPECIAL_DEDUCTIONS.put("医疗", new BigDecimal("200"));
        SPECIAL_DEDUCTIONS.put("失业", new BigDecimal("50"));
        SPECIAL_DEDUCTIONS.put("住房", new BigDecimal("1200"));
        SPECIAL_DEDUCTIONS.put("子女教育", new BigDecimal("1000"));
        SPECIAL_DEDUCTIONS.put("继续教育", new BigDecimal("400"));
        SPECIAL_DEDUCTIONS.put("大病医疗", new BigDecimal("8000")); // 年度上限
        SPECIAL_DEDUCTIONS.put("房贷利息", new BigDecimal("1000"));
        SPECIAL_DEDUCTIONS.put("住房租金", new BigDecimal("1500"));
        SPECIAL_DEDUCTIONS.put("赡养老人", new BigDecimal("2000"));
    }
    
    /**
     * 计算年度个人所得税
     * @param annualIncome 年度总收入
     * @param specialDeductions 专项扣除金额
     * @param additionalDeductions 专项附加扣除
     * @return 计算结果
     */
    public static TaxResult calculateAnnualTax(
        double annualIncome, 
        double specialDeductions, 
        double additionalDeductions) {
        
        // 基本扣除费用（年度）
        final double BASIC_DEDUCTION = 60000;
        
        // 转换为BigDecimal确保精度
        BigDecimal income = BigDecimal.valueOf(annualIncome);
        BigDecimal special = BigDecimal.valueOf(specialDeductions);
        BigDecimal additional = BigDecimal.valueOf(additionalDeductions);
        BigDecimal basic = BigDecimal.valueOf(BASIC_DEDUCTION);
        
        // 计算应纳税所得额
        BigDecimal taxableIncome = income
            .subtract(special)
            .subtract(additional)
            .subtract(basic)
            .max(BigDecimal.ZERO); // 不能为负数
        
        // 查找适用税率
        TaxBracket bracket = findTaxBracket(taxableIncome.doubleValue());
        
        // 计算应纳税额
        BigDecimal taxAmount = taxableIncome
            .multiply(BigDecimal.valueOf(bracket.getRate()))
            .subtract(BigDecimal.valueOf(bracket.getQuickDeduction()));
        
        // 确保税额不为负数
        taxAmount = taxAmount.max(BigDecimal.ZERO);
        
        // 计算税后收入
        BigDecimal afterTaxIncome = income.subtract(taxAmount);
        
        return new TaxResult(
            income.doubleValue(),
            taxableIncome.doubleValue(),
            taxAmount.doubleValue(),
            afterTaxIncome.doubleValue(),
            bracket
        );
    }
    
    /**
     * 根据应纳税所得额查找适用税率
     */
    private static TaxBracket findTaxBracket(double taxableIncome) {
        for (TaxBracket bracket : TAX_BRACKETS) {
            if (taxableIncome >= bracket.getLowerBound() && 
                taxableIncome < bracket.getUpperBound()) {
                return bracket;
            }
        }
        return TAX_BRACKETS[TAX_BRACKETS.length - 1];
    }
    
    /**
     * 获取专项扣除标准
     */
    public static Map<String, BigDecimal> getSpecialDeductionStandards() {
        return new HashMap<>(SPECIAL_DEDUCTIONS);
    }
    
    /**
     * 税率档次类
     */
    public static class TaxBracket {
        private final double lowerBound;
        private final double upperBound;
        private final double rate;
        private final double quickDeduction;
        
        public TaxBracket(double lowerBound, double upperBound, 
                         double rate, double quickDeduction) {
            this.lowerBound = lowerBound;
            this.upperBound = upperBound;
            this.rate = rate;
            this.quickDeduction = quickDeduction;
        }
        
        // Getter方法
        public double getLowerBound() { return lowerBound; }
        public double getUpperBound() { return upperBound; }
        public double getRate() { return rate; }
        public double getQuickDeduction() { return quickDeduction; }
        
        @Override
        public String toString() {
            return String.format("税率: %.1f%%, 速算扣除数: %.0f", rate * 100, quickDeduction);
        }
    }
    
    /**
     * 计算结果类
     */
    public static class TaxResult {
        private final double totalIncome;          // 总收入
        private final double taxableIncome;        // 应纳税所得额
        private final double taxAmount;            // 应纳税额
        private final double afterTaxIncome;       // 税后收入
        private final TaxBracket taxBracket;       // 适用税率档次
        
        public TaxResult(double totalIncome, double taxableIncome, 
                        double taxAmount, double afterTaxIncome, 
                        TaxBracket taxBracket) {
            this.totalIncome = totalIncome;
            this.taxableIncome = taxableIncome;
            this.taxAmount = taxAmount;
            this.afterTaxIncome = afterTaxIncome;
            this.taxBracket = taxBracket;
        }
        
        // Getter方法
        public double getTotalIncome() { return totalIncome; }
        public double getTaxableIncome() { return taxableIncome; }
        public double getTaxAmount() { return taxAmount; }
        public double getAfterTaxIncome() { return afterTaxIncome; }
        public TaxBracket getTaxBracket() { return taxBracket; }
        
        @Override
        public String toString() {
            return String.format(
                "计算结果:\n" +
                "总收入: ¥%.2f\n" +
                "应纳税所得额: ¥%.2f\n" +
                "应纳税额: ¥%.2f\n" +
                "税后收入: ¥%.2f\n" +
                "适用税率: %s",
                totalIncome, taxableIncome, taxAmount, afterTaxIncome, taxBracket
            );
        }
    }
}

GUI 界面实现

界面部分把输入、结果和操作按钮拆开了，结构比较清楚。实际做桌面程序时，这样的布局比把所有组件堆在一起更容易维护，也更方便后面扩展历史记录、导出结果之类的功能。

package com.tax.calculator;

import javax.swing.*;
import javax.swing.border.TitledBorder;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.math.BigDecimal;
import java.util.Map;

/**
 * 个税计算器主界面
 */
public class TaxCalculatorFrame extends JFrame {
    
    private JTextField incomeField;
    private JTextField specialDeductionField;
    private JTextField additionalDeductionField;
    private JTextArea resultArea;
    private JComboBox<String> deductionTypeCombo;
    private JLabel standardLabel;
    
    public TaxCalculatorFrame() {
        initUI();
        initData();
    }
    
    private void initUI() {
        setTitle("个人所得税计算模拟器 v1.0");
        setSize(800, 600);
        setLocationRelativeTo(null);
        
        // 主面板
        JPanel mainPanel = new JPanel(new BorderLayout(10, 10));
        mainPanel.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
        
        // 输入面板
        mainPanel.add(createInputPanel(), BorderLayout.NORTH);
        
        // 结果面板
        mainPanel.add(createResultPanel(), BorderLayout.CENTER);
        
        // 按钮面板
        mainPanel.add(createButtonPanel(), BorderLayout.SOUTH);
        
        add(mainPanel);
    }
    
    private JPanel createInputPanel() {
        JPanel panel = new JPanel(new GridLayout(5, 2, 10, 10));
        panel.setBorder(BorderFactory.createTitledBorder(
            BorderFactory.createLineBorder(Color.GRAY),
            "个税计算参数输入",
            TitledBorder.LEFT,
            TitledBorder.TOP
        ));
        
        // 年度总收入
        panel.add(new JLabel("年度总收入 (¥):"));
        incomeField = new JTextField("120000");
        panel.add(incomeField);
        
        // 专项扣除
        panel.add(new JLabel("三险一金专项扣除 (¥):"));
        specialDeductionField = new JTextField("10000");
        panel.add(specialDeductionField);
        
        // 专项附加扣除
        panel.add(new JLabel("专项附加扣除 (¥):"));
        additionalDeductionField = new JTextField("3000");
        panel.add(additionalDeductionField);
        
        // 扣除标准查询
        panel.add(new JLabel("扣除项目查询:"));
        JPanel queryPanel = new JPanel(new FlowLayout(FlowLayout.LEFT));
        deductionTypeCombo = new JComboBox<>();
        queryPanel.add(deductionTypeCombo);
        standardLabel = new JLabel("标准: ¥0");
        queryPanel.add(standardLabel);
        panel.add(queryPanel);
        
        return panel;
    }
    
    private JScrollPane createResultPanel() {
        resultArea = new JTextArea();
        resultArea.setEditable(false);
        resultArea.setFont(new Font("宋体", Font.PLAIN, 14));
        resultArea.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
        
        JScrollPane scrollPane = new JScrollPane(resultArea);
        scrollPane.setBorder(BorderFactory.createTitledBorder("计算结果"));
        
        return scrollPane;
    }
    
    private JPanel createButtonPanel() {
        JPanel panel = new JPanel(new FlowLayout(FlowLayout.CENTER, 20, 10));
        
        // 计算按钮
        JButton calculateBtn = new JButton("计算个税");
        calculateBtn.setFont(new Font("微软雅黑", Font.BOLD, 14));
        calculateBtn.setBackground(new Color(70, 130, 180));
        calculateBtn.setForeground(Color.WHITE);
        calculateBtn.setPreferredSize(new Dimension(120, 40));
        
        calculateBtn.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                calculateTax();
            }
        });
        
        // 清除按钮
        JButton clearBtn = new JButton("清除结果");
        clearBtn.setFont(new Font("微软雅黑", Font.PLAIN, 14));
        clearBtn.setPreferredSize(new Dimension(120, 40));
        clearBtn.addActionListener(e -> clearResults());
        
        // 税率表按钮
        JButton rateTableBtn = new JButton("查看税率表");
        rateTableBtn.setFont(new Font("微软雅黑", Font.PLAIN, 14));
        rateTableBtn.setPreferredSize(new Dimension(120, 40));
        rateTableBtn.addActionListener(e -> showTaxRateTable());
        
        panel.add(calculateBtn);
        panel.add(clearBtn);
        panel.add(rateTableBtn);
        
        return panel;
    }
    
    private void initData() {
        // 初始化扣除类型下拉框
        Map<String, BigDecimal> standards = TaxCalculator.getSpecialDeductionStandards();
        for (String key : standards.keySet()) {
            deductionTypeCombo.addItem(key);
        }
        
        // 添加下拉框监听
        deductionTypeCombo.addActionListener(e -> {
            String selected = (String) deductionTypeCombo.getSelectedItem();
            if (selected != null) {
                BigDecimal standard = standards.get(selected);
                standardLabel.setText(String.format("标准: ¥%.2f", standard));
            }
        });
        
        // 默认选择第一个
        if (deductionTypeCombo.getItemCount() > 0) {
            deductionTypeCombo.setSelectedIndex(0);
        }
    }
    
    /**
     * 执行个税计算
     */
    private void calculateTax() {
        try {
            // 获取输入值
            double income = Double.parseDouble(incomeField.getText());
            double special = Double.parseDouble(specialDeductionField.getText());
            double additional = Double.parseDouble(additionalDeductionField.getText());
            
            // 验证输入
            if (income < 0 || special < 0 || additional < 0) {
                JOptionPane.showMessageDialog(this,
                    "输入值不能为负数！",
                    "输入错误",
                    JOptionPane.WARNING_MESSAGE);
                return;
            }
            
            // 执行计算
            TaxCalculator.TaxResult result = TaxCalculator.calculateAnnualTax(
                income, special, additional);
            
            // 显示结果
            displayResult(result);
            
        } catch (NumberFormatException ex) {
            JOptionPane.showMessageDialog(this,
                "请输入有效的数字！",
                "输入错误",
                JOptionPane.ERROR_MESSAGE);
        }
    }
    
    /**
     * 显示计算结果
     */
    private void displayResult(TaxCalculator.TaxResult result) {
        StringBuilder sb = new StringBuilder();
        sb.append("=== 个人所得税计算结果 ===\n\n");
        sb.append(String.format("年度总收入: ¥%,.2f\n", result.getTotalIncome()));
        sb.append(String.format("应纳税所得额: ¥%,.2f\n", result.getTaxableIncome()));
        sb.append(String.format("适用税率档次: %s\n", result.getTaxBracket()));
        sb.append(String.format("应纳个人所得税: ¥%,.2f\n", result.getTaxAmount()));
        sb.append(String.format("年度税后收入: ¥%,.2f\n\n", result.getAfterTaxIncome()));
        
        // 计算月度数据
        double monthlyTax = result.getTaxAmount() / 12;
        double monthlyAfterTax = result.getAfterTaxIncome() / 12;
        
        sb.append("=== 月度数据估算 ===\n");
        sb.append(String.format("月度平均纳税: ¥%,.2f\n", monthlyTax));
        sb.append(String.format("月度税后收入: ¥%,.2f\n\n", monthlyAfterTax));
        
        // 添加税务建议
        sb.append("=== 税务优化建议 ===\n");
        if (result.getTaxableIncome() > 0) {
            sb.append("1. 充分利用专项附加扣除项目\n");
            sb.append("2. 合理规划年度收入时间分布\n");
            sb.append("3. 符合条件的捐赠可税前扣除\n");
        } else {
            sb.append("当前收入无需缴纳个人所得税\n");
        }
        
        resultArea.setText(sb.toString());
        resultArea.setCaretPosition(0);
    }
    
    /**
     * 显示税率表
     */
    private void showTaxRateTable() {
        StringBuilder sb = new StringBuilder();
        sb.append("=== 个人所得税税率表（综合所得） ===\n\n");
        sb.append("级数 | 全年应纳税所得额 | 税率 | 速算扣除数\n");
        sb.append("----|-----------------|------|----------\n");
        
        TaxCalculator.TaxBracket[] brackets = new TaxCalculator.TaxBracket[]{
            new TaxCalculator.TaxBracket(0, 36000, 0.03, 0),
            new TaxCalculator.TaxBracket(36000, 144000, 0.10, 2520),
            new TaxCalculator.TaxBracket(144000, 300000, 0.20, 16920),
            new TaxCalculator.TaxBracket(300000, 420000, 0.25, 31920),
            new TaxCalculator.TaxBracket(420000, 660000, 0.30, 52920),
            new TaxCalculator.TaxBracket(660000, 960000, 0.35, 85920),
            new TaxCalculator.TaxBracket(960000, Double.MAX_VALUE, 0.45, 181920)
        };
        
        for (int i = 0; i < brackets.length; i++) {
            TaxCalculator.TaxBracket b = brackets[i];
            String range;
            if (b.getUpperBound() == Double.MAX_VALUE) {
                range = String.format("超过%,.0f元", b.getLowerBound());
            } else {
                range = String.format("%,.0f - %,.0f元", 
                    b.getLowerBound(), b.getUpperBound());
            }
            
            sb.append(String.format("%-4d| %-15s | %.1f%% | %,.0f元\n",
                i + 1, range, b.getRate() * 100, b.getQuickDeduction()));
        }
        
        sb.append("\n注：应纳税所得额 = 年度收入 - 6万元(基本扣除) - 专项扣除 - 专项附加扣除\n");
        
        resultArea.setText(sb.toString());
    }
    
    /**
     * 清除结果
     */
    private void clearResults() {
        resultArea.setText("");
    }
}

使用说明

运行环境要求

• Java 8 或更高版本
• 支持 Swing 的桌面环境

编译运行

# 编译所有 Java 文件
javac -d . com/tax/calculator/*.java

# 运行程序
java com.tax.calculator.PersonalIncomeTaxApp

程序功能演示

输入计算参数时，可以填写：

• 年度总收入
• 三险一金专项扣除
• 专项附加扣除

扣除标准查询则通过下拉框选择不同项目，界面会同步显示对应标准。计算完成后，结果区会展示年度收入、应纳税所得额、适用税率、应纳税额、税后收入，以及月度估算值。

点击'查看税率表'后，可以直接看到年度综合所得的 7 级税率信息，便于对照不同收入区间的适用规则。

核心算法说明

计算公式

应纳税所得额 = 年度收入 - 60000（基本减除费用） - 专项扣除 - 专项附加扣除
应纳税额 = 应纳税所得额 × 适用税率 - 速算扣除数

税率表算法

这里采用的是逐级累进税率的思路。程序先根据应纳税所得额定位对应档位，再套用该档位的税率和速算扣除数完成计算。这个实现方式简单直接，也比较适合做成桌面小工具。

项目扩展建议

这个版本已经能完成基本计算，但如果想继续打磨，下面几个方向会很实用：

• 数据持久化：增加文件保存和加载功能
• 历史记录：保留多次计算结果，方便回看
• 导出功能：支持导出为 PDF 或 Excel
• 联网更新：根据政策变化更新税率配置
• 图表展示：用图表把税额分布、税后收入变化展示出来

注意事项

• 这个程序是模拟器，实际报税请以官方系统为准
• 税率政策变化后，需要同步调整代码中的税率表和扣除逻辑
• 计算结果仅供参考，不构成税务建议

开源说明

项目可按开源方式自由使用、修改和分发。若你准备在此基础上继续扩展，建议先把税率表、扣除规则、输入校验这三块整理成独立模块，后续维护会轻松很多。

运行效果

由于这里无法直接展示图片，程序运行后的界面大致包括三块：

• 主界面：输入区、结果区和功能按钮
• 计算结果：展示各项税务数据和月度估算
• 税率表：展示完整的 7 级累进税率表

作者：TaxDeveloper

更新日期：2023 年 10 月