计算Python中的抵押贷款利息 [英] Calculating mortgage interest in Python

问题描述

我目前正在通过youtube上的视频教程来学习python，并且遇到了一个我似乎无法掌握的公式，因为对我来说似乎没有什么合适的。练习的基本概念是制作一个抵押计算器，要求用户输入3条信息，即贷款金额，利率和贷款期限（年）。

I am currently learning python through a video tutorial on youtube, and have come up against a formula I cannot seem to grasp, as nothing looks right to me. The basic concept of the excersise is to make a mortgage calculator that asks the user to input 3 pieces of information, Loan Amount, Interest Rate, and Loan Term (years)

然后计算向用户支付的每月费用。这是我的代码：

then it calculates the monthly payments to the user. here is my code:

__author__ = 'Rick'
# This program calculates monthly repayments on an interest rate loan/mortgage.

loanAmount = input("How much do you want to borrow? \n")
interestRate = input("What is the interest rate on your loan? \n")
repaymentLength = input("How many years to repay your loan? \n")

#converting the string input variables to float
loanAmount = float(loanAmount)
interestRate = float(interestRate)
repaymentLength = float(repaymentLength)

#working out the interest rate to a decimal number
interestCalculation = interestRate / 100

print(interestRate)
print(interestCalculation)

#working out the number of payments over the course of the loan period.
numberOfPayments = repaymentLength*12

#Formula
#M = L[i(1+i)n] / [(1+i)n-1]

#   * M = Monthly Payment (what were trying to find out)
#   * L = Loan Amount (loanAmount)
#   * I = Interest Rate (for an interest rate of 5%, i = 0.05 (interestCalculation)
#   * N = Number of Payments (repaymentLength)

monthlyRepaymentCost = loanAmount * interestCalculation * (1+interestCalculation) * numberOfPayments / ((1+interestCalculation) * numberOfPayments - 1)
#THIS IS FROM ANOTHER BIT OF CODE THAT IS SUPPOSE TO BE RIGHT BUT ISNT---
# repaymentCost = loanAmount * interestRate * (1+ interestRate) * numberOfPayments  / ((1 + interestRate) * numberOfPayments -1)

#working out the total cost of the repayment over the full term of the loan
totalCharge = (monthlyRepaymentCost * numberOfPayments) - loanAmount


print("You want to borrow £" + str(loanAmount) + " over " + str(repaymentLength) + " years, with an interest rate of " + str(interestRate) + "%!")

print("Your monthly repayment will be £" + str(monthlyRepaymentCost))

print("Your monthly repayment will be £%.2f " % monthlyRepaymentCost)

print("The total charge on this loan will be £%.2f !" % totalCharge)

一切正常，但是最后抛出的价值是完全错误的……一笔100英镑的贷款，利率超过10％ 1年不应该让我每月支付£0.83。我们将不胜感激，帮助我绕开这个方程式以帮助我理解。

Everything works, but the value it throws out at the end is completely wrong... a £100 loan with an interest rate of 10% over 1 year shouldn't be making me pay £0.83 per month. Any help in getting my head around this equation to help me understand would be greatly appreciated.

推荐答案

此

This mortgage package does it nicely:

>>> import mortgage
>>> m=mortgage.Mortgage(interest=0.0375, amount=350000, months=360)
>>> mortgage.print_summary(m)
                     Rate:      0.037500
             Month Growth:      1.003125
                      APY:      0.038151
             Payoff Years:            30
            Payoff Months:           360
                   Amount:     350000.00
          Monthly Payment:       1620.91
           Annual Payment:      19450.92
             Total Payout:     583527.60

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