Python：计算贷款付款的更智能方法

Question

如何计算贷款月费？

给出的是：

• a：贷款金额。
• b：贷款期限（月数）。
• c：利率pa（利息按月计算加算，加1/12的利息。所以如果利息是12%，每月加1%的利息）。
• d：期末后所欠金额。

这个问题与通常的问题有点不同，因为目标不是在贷款期结束后偿还贷款，而是仍然欠所给的金额。如果我想支付全部金额，我已经能够找到一种算法来解决问题，但它当然不适用于这个问题，因为目标是最终欠给定金额而不是不欠任何东西。

我设法通过猜测开始解决这个问题，然后继续改进这个猜测，直到它足够接近。然而我想知道是否有更好的方法来简单地计算这个，而不仅仅是猜测。

编辑：这就是我现在的做法。

def find_payment(start, end, months, interest):
    difference = start
    guess = int(start / months * interest)
    while True:
        total = start
        for month in range(1, months + 1):
            ascribe = total * interest / 12
            total = total + ascribe - guess
        difference = total - end
        # See if the guess was good enough.
        if abs(difference) > start * 0.001:
            if difference < 0:
                if abs(difference) < guess:
                    print "payment is %s" % guess
                    return evolution(start, guess, interest, months)
                else:
                    mod = int(abs(difference) / start * guess)
                    if mod == 0:
                        mod = 1
                    guess -= mod
            else:
                mod = int(difference / start * guess)
                if mod == 0:
                    mod = 1
                guess += mod
        else:
            print "payment is %s" % guess
            return evolution(start, guess, interest, months)

进化只是一个函数，它显示贷款的付款方式和利息的利息，汇总支付的利息总额等。

一个例子如果我想找出一笔从 10 万美元开始到 5 万美元结束、利息为 8%、期限为 70 个月的贷款每月还款额，调用

>>> find_payment(100000, 50000, 70, 0.08)
payment is 1363

在上述情况下，我最终会欠 49935，并且我循环了5次。通过循环所需的次数取决于我想要达到的次数有多接近，并且它会略有不同。

Answer 1

这基本上是一个抵押贷款还款计算。

假设开始大于结束，并且利息在 0 到 1 之间（即 10% 利息为 0.1）

首先考虑您想要还清的付款部分。

Principal = start - end

每月还款额由下式给出：

pay_a = (interest / 12) / (1 - (1+interest/12) ^ (-months))) * Principal

然后您需要考虑额外的利息。这正好等于剩余本金乘以每月利息

pay_b = interest / 12 * end

所以总还款额是

payment = (interest / 12) * (1 / (1 - (1+interest/12) ^ (-months))) * Principal + end)

在您给出的示例中

Start: 100000
End:  50000
Months: 70
Interest: 8% 
pay_a = 896.20
pay_b = 333.33
Payment = 1229.54

当我在 Excel 中测试这些值时，在 70 次还款后，剩余贷款为 50,000。这是假设您在每月付款之前支付名义利息。

Answer 2

也许考虑这个问题的最简单的方法是将贷款分成两部分，一部分需要全额偿还，另一部分则不需要偿还任何东西。您已经计算了第一部分的月费。

Answer 3

您可以继续支付每个月的利息；那么，你将永远欠同样的金额。

Owe_1 = a

Int_2 = Owe_1*(InterestRate/12)
Pay_2 = Int_2
Owe_2 = Owe_1 + Int_2 - Pay_2 # ==> Owe_1 + Int_2 - Int_2 = Owe_1

Int_3 = Owe_2*(InterestRate/12)
Pay_3 = Int_3
Owe_3 = Owe_2 + Int_3 - Pay_3 # ==> Owe_2 + Int_3 - Int_3 = Owe_2 = Owe_1

Answer 4

计算 emi 的 python 代码

class EMI_CALCULATOR(object):
 # Data attributes
 # Helps to calculate EMI

  Loan_amount = None # assigning none values
  Month_Payment = None # assigning none values
  Interest_rate = None #assigning none values
  Payment_period = None #assigning none values

  def get_loan_amount(self):
 #get the  value of loan amount
      self.Loan_amount = input("Enter The Loan amount(in rupees) :")
      pass

  def get_interest_rate(self):
   # get the value of interest rate
      self.Interest_rate = input("Enter The Interest rate(in percentage(%)) : ")
      pass

  def get_payment_period(self):
   # get the payment period"
      self.Payment_period = input("Enter The Payment period (in month): ")
      pass


  def calc_interest_rate(self):
  # To calculate the  interest rate"
      self.get_interest_rate()

      if self.Interest_rate > 1:
         self.Interest_rate = (self.Interest_rate /100.0) 

      else:
         print "You have not entered The interest rate correctly ,please try again "
      pass

  def calc_emi(self):
  # To calculate the EMI"          

      try:

        self.get_loan_amount() #input loan amount 
        self.get_payment_period() #input payment period
        self.calc_interest_rate() #input interest rate and calculate the interest rate

      except NameError:
             print "You have not entered Loan amount (OR) payment period (OR) interest rate  correctly,Please enter and try again. "

      try:
        self.Month_Payment = (self.Loan_amount*pow((self.Interest_rate/12)+1,
                             (self.Payment_period))*self.Interest_rate/12)/(pow(self.Interest_rate/12+1,
                             (self.Payment_period)) - 1)

      except ZeroDivisionError: 
                    print "ERROR!! ZERO DIVISION ERROR , Please enter The Interest rate correctly and Try again."

      else:
         print "Monthly Payment is : %r"%self.Month_Payment
      pass


  if __name__ == '__main__':# main method 

        Init = EMI_CALCULATOR() # creating  instances


        Init.calc_emi() #to calculate EMI

了解更多信息，请访问：

Answer 5

这是一个相当详细的方式，但也会给出全部付款

# Mortgage Loan that gives the balance and total payment per year

# Function that gives the monthly payment
def f1 (principle,annual_interest_rate,duration):
    r = annual_interest_rate/1200
    n = duration*12
    a=principle*r*((1+r)**n)
    b= (((1+r)**n)- 1)
    if r > 0 :
        MonthlyPayment = (a/b)
    else :
        MonthlyPayment = principle/n

    return MonthlyPayment

# Function that gives the balance
def f2 (principle,annual_interest_rate,duration,number_of_payments):
    r = annual_interest_rate/1200
    n = duration*12
    a= ((1+r)**n)
    b= ((1+r)**number_of_payments)
    c= (((1+r)**n)-1)
    if r > 0 :
        RemainingLoanBalance = principle*((a-b)/c)
    else :
        RemainingLoanBalance = principle*(1-(number_of_payments/n))

    return RemainingLoanBalance
# Entering the required values
principle=float(input("Enter loan amount: "))
annual_interest_rate=float(input("Enter annual interest rate (percent): "))
duration=int(input("Enter loan duration in years: "))

# Output that returns all useful data needed
print ("LOAN AMOUNT:",principle,"INTEREST RATE (PERCENT):",annual_interest_rate)
print ("DURATION (YEARS):",duration,"MONTHLY PAYMENT:",int(f1(principle,annual_interest_rate,duration)))


k=duration+1
BALANCE=principle
total=0
for i in range (1,k):
    TOTALPAYMENT= f1(BALANCE,annual_interest_rate,k-i)*12
    total+= TOTALPAYMENT
    BALANCE= f2(principle,annual_interest_rate,duration,12*i)
    print("YEAR:",i,"BALANCE:",int(BALANCE),"TOTAL PAYMENT",int(total))

Answer 6

这个怎么样？

def EMI_calc(principle, rate, time, frequency):
    return (principle / ((1-((1+(rate/frequency))**(-1*(time*frequency))))/(rate/frequency)))

print("""
----- Welcome to EMI programe for Python -----
""")
print("\n You have chosen to know the EMI for Loan.\n")
input('\nTo Continue Press ENTER --- to ABORT Press ctrl+c > \n')

print("\nPlease Enter amount of Loan to be taken: >\n")
principle = int(input())
print("\nEnter rate of interst (%): >\n")
rate = float(input())/100
print("\nEnter Term (Years): >\n")
time = float(input())
print("\nPlease enter the frequency of installments) : >\n")
frequency = int(input())

EMI = round(EMI_calc(principle, rate, time, frequency),0)

print("""

---------------------------------------------------------------------

""")
print(f"""
The EMI for Loan of Rs.{principle};
at interest rate of {rate*100} % for {time} years;
would be: Rs.""", EMI)

print("""

---------------------------------------------------------------------

""")

Answer 7

这是使用 numpy 函数的代码片段。这会显示每月的还款额、本金、利息、分期付款和总金额。运行它并查看输出。您还可以检查 Excel“IPMT()”和“PPMT()”函数的语法，以获取参数的更多说明。
https://docs。 scipy.org/doc/numpy-1.13.0/reference/ generated/numpy.pmt.html#numpy.pmt

import math
import numpy as np
rate = 0.08
start_amount = 100000.0
end_amount = 50000.0
diff_amount = start_amount - end_amount
# nr_years = 4
payment_frequency = int (12)
nr_months = 70 # = nr_years * payment_frequency
per_np = np.arange (nr_months) + 1 # +1 because index starts with 1 here
pay_b = rate / payment_frequency * end_amount
ipmt_np = np.ipmt (rate / payment_frequency, per_np, nr_months, diff_amount) - pay_b
ppmt_np = np.ppmt (rate / payment_frequency, per_np, nr_months, diff_amount)
for payment in per_np:
    idx = payment - 1
    principal = math.fabs (ppmt_np [idx])
    start_amount = start_amount - principal
    interest = math.fabs (ipmt_np [idx])
    instalment = principal + interest
    print payment, "\t", principal, "\t", interest, "\t\t", instalment, "\t\t", start_amount
print np.sum (ipmt_np)