interest

gistfile1.txt

#!/usr/bin/env python3

from decimal import Decimal, ROUND_HALF_EVEN

def calculate_daily_accrual_monthly_compound(principal, annual_rate, time_years):
    """
    Calculate interest with daily accrual and monthly compounding.
    Uses banker's rounding (ROUND_HALF_EVEN) for all calculations.

    Args:
        principal: Starting principal amount
        annual_rate: Annual interest rate (percentage)
        time_years: Time period in years

    Returns:
        tuple: (final_balance, total_interest_earned)
    """
    # Convert to Decimal for precise calculations
    balance = Decimal(str(principal))
    annual_rate_decimal = Decimal(str(annual_rate)) / Decimal('100')
    daily_rate = annual_rate_decimal / Decimal('365')

    # Calculate total days and months
    total_days = int(time_years * 365)
    total_months = int(time_years * 12)

    accrued_interest = Decimal('0')

    for month in range(total_months):
        # Determine days in this month (approximate 30.42 days/month average)
        days_in_month = 30 if month < total_months - 1 else (total_days - month * 30)

        # Accrue interest daily for this month
        for _ in range(days_in_month):
            daily_interest = (balance * daily_rate).quantize(
                Decimal('0.00000001'), rounding=ROUND_HALF_EVEN
            )
            accrued_interest += daily_interest

        # print accrued interest for the month with 8 decimal places
        print(f"Month {month + 1}: Accrued Interest: ${accrued_interest:.8f}")

        # Apply accrued interest at end of month (round to 2 decimal places)
        balance += accrued_interest.quantize(Decimal('0.01'), rounding=ROUND_HALF_EVEN)
        accrued_interest = Decimal('0')

        # Print the principal after compounding for the month
        print(f"Month {month + 1}: New Balance: ${balance:.2f}")

    total_interest = balance - Decimal(str(principal))
    return balance, total_interest

def main():
    print("Interest Calculator")
    print("Daily Accrual with Monthly Compounding")
    print("-" * 40)

    # Get user input
    principal = float(input("Enter principal amount: $"))
    rate = float(input("Enter annual interest rate (%): "))
    time = float(input("Enter time period (years): "))

    # Calculate with daily accrual and monthly compounding
    final_balance, total_interest = calculate_daily_accrual_monthly_compound(
        principal, rate, time
    )

    print("\n" + "=" * 40)
    print("INTEREST CALCULATION")
    print("Daily Accrual | Monthly Compounding")
    print("Banker's Rounding (Round Half Even)")
    print("=" * 40)
    print(f"Starting Principal: ${Decimal(str(principal)):,.2f}")
    print(f"Interest Earned:    ${total_interest:,.2f}")
    print(f"Final Balance:      ${final_balance:,.2f}")
    print(f"\nEffective Rate:     {(total_interest / Decimal(str(principal)) / Decimal(str(time)) * 100):.4f}% per year")

if __name__ == "__main__":
    main()