mortgage_calculator.py

from decimal import *

MONTHS_IN_A_YEAR = Decimal(12)

LOAN_TERM_YEARS = Decimal(30)
HOME_PRICE = Decimal(550000)
DOWN_PAYMENT = Decimal(50000)
INTEREST_RATE = Decimal(.030)

OPPORTUNITY_INITIAL_INVESTMENT = Decimal(5000)
OPPORTUNITY_INTEREST_RATE = Decimal(.07)

INITIAL_LOAN_PRINCIPAL = HOME_PRICE - DOWN_PAYMENT
REMAINING_LOAN_PRINCIPAL = INITIAL_LOAN_PRINCIPAL
INTEREST_RATE_PER_MONTH = INTEREST_RATE / MONTHS_IN_A_YEAR
NUMBER_OF_PAYMENTS = LOAN_TERM_YEARS * MONTHS_IN_A_YEAR

# IDK this part
numerator = INTEREST_RATE_PER_MONTH * ((1 + INTEREST_RATE_PER_MONTH) ** NUMBER_OF_PAYMENTS)
denominator = ((1 + INTEREST_RATE_PER_MONTH) ** NUMBER_OF_PAYMENTS) - 1
TOTAL_PAYMENT = INITIAL_LOAN_PRINCIPAL * (numerator / denominator)

print(f"Total payment: {TOTAL_PAYMENT:.2f}")

total_interest_paid = 0
opportunity_balance = OPPORTUNITY_INITIAL_INVESTMENT

for month_index in range(int(NUMBER_OF_PAYMENTS)):
    current_month = month_index + 1
    print(f"----- MONTH: {current_month} -----")

    interest_payment = REMAINING_LOAN_PRINCIPAL * INTEREST_RATE_PER_MONTH
    total_interest_paid += interest_payment
    print(f"Interest payment: {interest_payment:.2f}")

    principal_payment = TOTAL_PAYMENT - interest_payment
    print(f"Principal payment: {principal_payment:.2f}")

    REMAINING_LOAN_PRINCIPAL = REMAINING_LOAN_PRINCIPAL - principal_payment
    print(f"Remaining loan principal: {REMAINING_LOAN_PRINCIPAL:.2f}")

    if current_month % MONTHS_IN_A_YEAR == 0:
        print("At the year, compounding interest...")
        opportunity_balance = opportunity_balance + (opportunity_balance * OPPORTUNITY_INTEREST_RATE)

print()
print(f"Total interest paid: {total_interest_paid:.2f}")
print(f"Total paid: {(total_interest_paid + INITIAL_LOAN_PRINCIPAL):.2f}")
print(f"Opportunity balance: {opportunity_balance:.2f}")