Payback Period Calculator

import math

def calculate_payback_periods(investment, annual_cf, discount_rate_pct):
    """
    Calculate Simple and Discounted Payback Periods.
    """
    if investment < 0 or annual_cf <= 0:
        raise ValueError("Invalid inputs")

    simple_payback = investment / annual_cf
    
    r = discount_rate_pct / 100.0
    
    if r == 0:
        return simple_payback, simple_payback
        
    # Check if investment will ever be paid back
    if annual_cf <= investment * r:
        discounted_payback = float('inf')
    else:
        discounted_payback = -math.log(1 - (investment * r) / annual_cf) / math.log(1 + r)
        
    return simple_payback, discounted_payback

# Example Parameters
Inv = 150000
CF = 45000
Rate = 8

simple, discounted = calculate_payback_periods(Inv, CF, Rate)

print(f"Simple Payback: {simple:.2f} years")
if discounted == float('inf'):
    print("Discounted Payback: Never pays back")
else:
    print(f"Discounted Payback: {discounted:.2f} years")

function [simple, discounted] = payback_period(Inv, CF, Rate)
    % Calculate Simple and Discounted Payback Periods
    
    if Inv < 0 || CF <= 0
        error('Invalid inputs');
    end

    simple = Inv / CF;
    r = Rate / 100;
    
    if r == 0
        discounted = simple;
        return;
    end
    
    if CF <= Inv * r
        discounted = Inf;
    else
        discounted = -log(1 - (Inv * r) / CF) / log(1 + r);
    end
end

% Example Parameters
Inv = 150000;
CF = 45000;
Rate = 8;

[simple, discounted] = payback_period(Inv, CF, Rate);
fprintf('Simple Payback: %.2f years\n', simple);
fprintf('Discounted Payback: %.2f years\n', discounted);