BuildCalc Pro

Mortgage Repayment Calculator

Calculate your monthly mortgage payments, total interest, and see how extra payments can save you thousands. Includes yearly amortization schedule.

How to Use This Calculator

1. Enter your loan amount (or home price minus down payment). 2. Set the interest rate and loan term in years. 3. Optionally add extra monthly payments to see savings. 4. Add property tax and insurance for total monthly cost. 5. Click Calculate to see your payment breakdown and amortization.

Key Formulas

Monthly Payment (P&I)

P × [r(1+r)^n] / [(1+r)^n – 1]

P = loan amount, r = monthly rate (annual ÷ 12), n = total months.

Total Interest Paid

(Monthly Payment × Total Months) – Loan Amount

Total of all payments minus the original principal borrowed.

Remaining Balance

P × [(1+r)^n – (1+r)^p] / [(1+r)^n – 1]

P = original loan, n = total months, p = payments made so far.

Mortgage Payments Explained: Principal, Interest & Extra Payments

Understanding how mortgage payments work helps you save tens of thousands of dollars over the life of your loan. Each monthly payment is split between principal (paying down your balance) and interest (the cost of borrowing). In early years, 70–80% goes to interest.

On a $300,000 mortgage at 6.5% for 30 years, your monthly P&I payment is $1,896. Over 30 years, you will pay $382,633 in total interest — more than the original loan amount. The total cost of the home becomes $682,633.

Extra payments can dramatically reduce your total interest and payoff time. Adding just $200/month to the same loan saves over $72,000 in interest and pays off the mortgage 5 years early. Even one extra payment per year (splitting monthly payment into biweekly) saves $50,000+.

Choosing a 15-year term instead of 30 years roughly doubles your monthly payment but cuts total interest by 60–65%. A $300,000 loan at 6% costs $455,000 in interest over 30 years but only $156,000 over 15 years.

Refinancing makes sense when you can lower your rate by at least 0.75–1%, plan to stay long enough to recoup closing costs (typically 2–5% of loan amount), and your break-even point is within your expected stay.

Frequently Asked Questions

How much of my payment goes to principal vs interest?

In year 1 of a 30-year loan at 6.5%, about 72% goes to interest. By year 15, its roughly 50/50. By year 25, about 75% goes to principal. This is why extra payments in early years have the biggest impact.

Is it worth making extra mortgage payments?

Yes, especially in the first 10 years when most of your payment goes to interest. An extra $200/month on a $300,000 loan at 6.5% saves $72,000+ in interest. However, if your rate is below 4–5%, investing the extra money may yield better returns.

What is an amortization schedule?

An amortization schedule is a table showing every payment over the life of the loan, broken down by principal, interest, and remaining balance. It reveals how slowly equity builds in early years and how extra payments accelerate the process.

Should I get a 15-year or 30-year mortgage?

A 15-year mortgage has lower rates (typically 0.5–0.75% less) and saves 60%+ in interest, but monthly payments are roughly double. Choose 30-year if you need lower payments for cash flow, and make extra payments when possible to get 15-year benefits with 30-year flexibility.