Interest calculator in Python. Find total sum and how much to pay each year

If you don't want to do the calculations yourself, you could make use of numpy.

>>> import numpy as np
>>> np.pmt(.05,5,-50000)
11548.739906413395

The above gives the annual payment.

So, for the first year, the amount of principal and interest paid would be:

interest = 50000*.05

principal_paid = 11548.74 - interest

Here is a small program that does that.

import numpy as np

interest = .05
principal = 50000
years = 5

annual_pay = np.pmt(interest,years,-principal)

print('{}{:>10}{:>10}{:>10}'.format('year','interest','retired', 'balance'))

for yr in range(1,6):
    i = interest * principal
    retired_prin = annual_pay - i
    principal = principal - retired_prin
    print('{:>4}{:>10.2f}{:>10.2f}{:>10.2f}'
          .format(yr, i, retired_prin, principal))
    

This prints:

year  interest   retired   balance
   1   2500.00   9048.74  40951.26
   2   2047.56   9501.18  31450.08
   3   1572.50   9976.24  21473.85
   4   1073.69  10475.05  10998.80
   5    549.94  10998.80     -0.00