Extra Mortgage Payment Calculator

Making extra payments on your mortgage is one of the highest guaranteed-return financial moves available to homeowners. Every extra dollar of principal you pay reduces the balance on which future interest is charged — and because mortgages are front-loaded with interest, extra payments early in the loan have the most impact.

Formula: Monthly Interest = Remaining Principal × (Annual Rate ÷ 12) Principal Reduction = Monthly Payment − Monthly Interest Interest Saved = Standard Total Interest − New Total Interest (with extra payments) Time Saved = Standard Loan Term − New Payoff Month

How amortization works: In the early years of a 30-year mortgage, most of each payment is interest. On a $300,000 loan at 7%, month 1’s payment of ~$1,996 breaks down as:

• Interest: $300,000 × (0.07 ÷ 12) = $1,750
• Principal: $1,996 − $1,750 = $246

Every extra dollar you pay goes 100% to principal reduction.

Worked example: $300,000 mortgage, 7% interest, 30-year term. Standard monthly payment: $1,995.91 Total interest over 30 years: $418,527

Adding $200/month extra from day one: New payoff time: ~24 years and 2 months (saves 5 years 10 months) Total interest paid: ~$328,000 Interest saved: ~$90,527

Adding $500/month extra: New payoff: ~20 years 3 months (saves 9 years 9 months) Interest saved: ~$163,000

One extra payment per year: If you make 13 payments instead of 12 annually (or split the extra monthly — add 1/12 of a payment each month): Payoff accelerated by approximately 4.5 years on a 30-year mortgage. Interest saved: ~$60,000–$75,000.

Important considerations:

• Check your loan for prepayment penalties (rare but still exist in some loans).
• Verify extra payments are applied to principal, not future payments — specify this in writing.
• Compare the guaranteed 7% “return” of paying down your mortgage vs. investing the extra in a broad index fund (historically ~10% returns but with volatility and risk).