How to Calculate Mortgage Payments Like a Pro

The Mortgage Payment Formula

Your monthly mortgage payment is calculated using this formula:

M = P[r(1+r)n] / [(1+r)n - 1]

• M = Monthly payment
• P = Principal (the loan amount)
• r = Monthly interest rate (annual rate divided by 12)
• n = Total number of payments (loan term in years multiplied by 12)

For example, a $300,000 loan at 6.5% annual interest for 30 years gives you a monthly rate of 0.005417 and 360 total payments, resulting in approximately $1,896 per month.

How Amortization Works

In the early years of your mortgage, most of each payment goes toward interest rather than the principal balance. Over time, the split gradually shifts so that more of your payment reduces the principal. This is why a 30-year mortgage on $300,000 at 6.5% results in paying roughly $382,000 in total interest over the life of the loan.

The Power of Extra Payments

Making extra payments directly reduces your principal, which means less interest accumulates in future months. Even an additional $100 per month on the example above could save you over $50,000 in interest and shorten your loan by about 5 years. Some effective strategies include:

• Rounding up your payment to the nearest hundred
• Making one extra full payment each year
• Applying windfalls like tax refunds to your principal

Always confirm with your lender that extra payments are applied to the principal balance and not to future interest.