Personal finances are an important part of life. Sometimes you need some extra money and decide to take a loan, or you want to buy a house using a mortgage. To make an informed decision, you need to be able to calculate different financial parameters. I have made a program that can help you make these informed decisions!
The project below was written in Python and it is the backend component of a loan calculator. It can be inplemented in a web application or it can be used as the backend of a stand alone mobile application.
Code
import argparse
import math
pay_type = None
payment = None
principal = None
periods = None
interest = None
def main():
parser = argparse.ArgumentParser()
parser.add_argument('--type', help='the type of payments: "annuity" or "diff" (differentiated)')
parser.add_argument('--payment', help='monthly payment', type=int)
parser.add_argument('--principal', help='to calculate payment', type=int)
parser.add_argument('--periods', help='the number of months and/or years needed to repay the credit', type=int)
parser.add_argument('--interest', help='is specified without a percent sign', type=float)
if parse_args(parser.parse_args()):
if pay_type == 'annuity':
if payment is None:
calculate_payment()
elif principal is None:
calculate_principal()
elif periods is None:
calculate_periods()
elif pay_type == "diff":
calculate_differentiated()
else:
print('Incorrect parameters')
def parse_args(args):
global pay_type
global payment
global principal
global periods
global interest
if args.principal and args.principal >= 0:
principal = args.principal
if args.periods and args.periods >= 0:
periods = args.periods
if args.interest and args.interest >= 0.0:
interest = args.interest
if args.type:
pay_type = args.type
if args.type == "annuity":
if args.payment and args.payment >= 0:
payment = args.payment
if (principal is None and periods is None) or \
(periods is None and payment is None) or \
(payment is None and principal is None):
return False
return True
elif args.type == "diff":
if args.payment:
return False
elif principal is not None and periods is not None:
return True
return False
def calculate_payment():
i = interest / 100 / 12
annuity = principal * ((i * pow((1 + i), periods)) / (pow((1 + i), periods) - 1))
over = math.ceil(annuity) * periods - principal
print(f'Your annuity payment = {math.ceil(annuity)}!')
print(f'Overpayment = {over}')
def calculate_principal():
i = interest / 100 / 12
P = payment / ((i * pow((1 + i), periods)) / (pow((1 + i), periods) - 1))
over = payment * periods - math.floor(P)
print(f'Your credit principal = {math.floor(P)}!')
print(f'Overpayment = {over}')
def calculate_periods():
i = interest / 100 / 12
n = math.ceil(math.log(payment / (payment - i * principal), 1 + i))
q, r = divmod(n, 12)
year_str = 'year'
if q > 1:
year_str += 's'
month_str = 'month'
if r > 1:
month_str += 's'
over = payment * n - principal
if r > 0:
print(f'You need {q} {year_str} and {r} {month_str} to repay this credit!')
else:
print(f'You need {q} {year_str} to repay this credit!')
print(f'Overpayment = {over}')
def calculate_differentiated():
i = interest / 100 / 12
total = 0
for m in range(1, periods + 1):
D = principal / periods + i * (principal - principal * (m - 1) / periods)
total += math.ceil(D)
print(f'Month {m}: paid out {math.ceil(D)}')
print()
over = total - principal
print(f'Overpayment = {over}')
if __name__ == '__main__':
main()