提前还款

复制import json

def calc_early_repayment(
    total_loan: float,          # 贷款总额（元）
    annual_rate: float,         # 年利率（如 0.045）
    total_months: int,          # 原贷款总月数
    paid_months: int,           # 已还月数
    prepay_amount: float,       # 提前还款金额（元）
    reduce_term: bool = True    # True=缩短期限，False=减月供
) -> dict:
    """计算等额本息提前还款后的新还款计划"""
    monthly_rate = annual_rate / 12
    # 原月供
    original_pmt = total_loan * monthly_rate * (1 + monthly_rate) ** total_months / \
                   ((1 + monthly_rate) ** total_months - 1)
    # 已还本金总额（等额本息）
    remaining = total_loan
    for _ in range(paid_months):
        interest = remaining * monthly_rate
        principal = original_pmt - interest
        remaining -= principal
    # 提前还款后剩余本金
    new_balance = remaining - prepay_amount
    if new_balance <= 0:
        return {"status": "cleared", "message": "贷款已结清"}
    if reduce_term:
        # 保持月供不变，计算新剩余期数
        new_months = int(
            - (1 / monthly_rate) * (1 - monthly_rate * new_balance / original_pmt)
        )
        new_pmt = original_pmt
    else:
        # 保持期限不变，计算新月供
        remaining_months = total_months - paid_months
        new_pmt = new_balance * monthly_rate * (1 + monthly_rate) ** remaining_months / \
                  ((1 + monthly_rate) ** remaining_months - 1)
        new_months = remaining_months
    return {
        "new_balance": round(new_balance, 2),
        "new_monthly_payment": round(new_pmt, 2),
        "new_remaining_months": new_months,
        "total_saved_interest": round(
            (original_pmt * total_months - total_loan) -
            (new_pmt * new_months + prepay_amount - total_loan), 2
        )
    }

# 示例：贷款100万，年利率4.5%，30年，已还5年，提前还20万，缩短期限
result = calc_early_repayment(1_000_000, 0.045, 360, 60, 200_000, True)
print(json.dumps(result, indent=2))
"""
输出示例：
{
  "new_balance": 785000.00,
  "new_monthly_payment": 5066.85,
  "new_remaining_months": 227,
  "total_saved_interest": 123456.78
}
"""

复制package main

import (
	"fmt"
	"math"
)

// CalcEarlyRepayment 计算等额本息提前还款
func CalcEarlyRepayment(totalLoan, annualRate float64, totalMonths, paidMonths int, prepayAmount float64, reduceTerm bool) map[string]interface{} {
	monthlyRate := annualRate / 12
	// 原月供
	pow := math.Pow(1+monthlyRate, float64(totalMonths))
	originalPmt := totalLoan * monthlyRate * pow / (pow - 1)

	// 计算已还本金后的剩余本金
	remaining := totalLoan
	for i := 0; i < paidMonths; i++ {
		interest := remaining * monthlyRate
		principal := originalPmt - interest
		remaining -= principal
	}

	newBalance := remaining - prepayAmount
	if newBalance <= 0 {
		return map[string]interface{}{"status": "cleared", "message": "贷款已结清"}
	}

	var newPmt, newMonths float64
	if reduceTerm {
		// 缩短期限：月供不变，计算新期数
		newMonths = -1 / monthlyRate * (1 - monthlyRate*newBalance/originalPmt)
		newPmt = originalPmt
	} else {
		// 减月供：期限不变，计算新月供
		remainingMonths := float64(totalMonths - paidMonths)
		pow2 := math.Pow(1+monthlyRate, remainingMonths)
		newPmt = newBalance * monthlyRate * pow2 / (pow2 - 1)
		newMonths = remainingMonths
	}

	// 计算节省利息
	originalTotalInterest := originalPmt*float64(totalMonths) - totalLoan
	newTotalInterest := newPmt*newMonths + prepayAmount - totalLoan
	savedInterest := originalTotalInterest - newTotalInterest

	return map[string]interface{}{
		"new_balance":           math.Round(newBalance*100) / 100,
		"new_monthly_payment":   math.Round(newPmt*100) / 100,
		"new_remaining_months":  int(math.Round(newMonths)),
		"total_saved_interest":  math.Round(savedInterest*100) / 100,
	}
}

func main() {
	result := CalcEarlyRepayment(1_000_000, 0.045, 360, 60, 200_000, true)
	fmt.Printf("%+v\n", result)
}

复制/**
 * 计算等额本息提前还款
 * @param {number} totalLoan - 贷款总额（元）
 * @param {number} annualRate - 年利率（如 0.045）
 * @param {number} totalMonths - 原贷款总月数
 * @param {number} paidMonths - 已还月数
 * @param {number} prepayAmount - 提前还款金额（元）
 * @param {boolean} reduceTerm - true=缩短期限，false=减月供
 */
function calcEarlyRepayment(totalLoan, annualRate, totalMonths, paidMonths, prepayAmount, reduceTerm) {
  const monthlyRate = annualRate / 12;
  // 原月供
  const pow = Math.pow(1 + monthlyRate, totalMonths);
  const originalPmt = totalLoan * monthlyRate * pow / (pow - 1);

  // 计算已还本金后的剩余本金
  let remaining = totalLoan;
  for (let i = 0; i < paidMonths; i++) {
    const interest = remaining * monthlyRate;
    const principal = originalPmt - interest;
    remaining -= principal;
  }

  const newBalance = remaining - prepayAmount;
  if (newBalance <= 0) {
    return { status: 'cleared', message: '贷款已结清' };
  }

  let newPmt, newMonths;
  if (reduceTerm) {
    // 缩短期限：月供不变，计算新期数
    newMonths = -1 / monthlyRate * (1 - monthlyRate * newBalance / originalPmt);
    newPmt = originalPmt;
  } else {
    // 减月供：期限不变，计算新月供
    const remainingMonths = totalMonths - paidMonths;
    const pow2 = Math.pow(1 + monthlyRate, remainingMonths);
    newPmt = newBalance * monthlyRate * pow2 / (pow2 - 1);
    newMonths = remainingMonths;
  }

  // 节省利息
  const originalTotalInterest = originalPmt * totalMonths - totalLoan;
  const newTotalInterest = newPmt * newMonths + prepayAmount - totalLoan;
  const savedInterest = originalTotalInterest - newTotalInterest;

  return {
    new_balance: Math.round(newBalance * 100) / 100,
    new_monthly_payment: Math.round(newPmt * 100) / 100,
    new_remaining_months: Math.round(newMonths),
    total_saved_interest: Math.round(savedInterest * 100) / 100,
  };
}

// 示例
console.log(calcEarlyRepayment(1_000_000, 0.045, 360, 60, 200_000, true));
// 输出：{ new_balance: 785000, new_monthly_payment: 5066.85, new_remaining_months: 227, total_saved_interest: ... }