Extra payment mortgage calculator

How Much Do Extra Mortgage Payments Save?

Even small extra payments compound into major savings, because every extra dollar goes straight to principal — permanently lowering the balance your interest is calculated on. Here's what different extra payment strategies save on a $300,000, 30-year fixed mortgage at 7% interest:

Your actual savings depend on your loan amount, interest rate, and how early in the loan you start. Extra payments made in the first years of a mortgage save the most, because that's when the largest share of each standard payment goes to interest. Enter your own numbers in the calculator above to see your exact payoff date and savings.

Extra Principal Payments: Make Sure Your Money Goes to the Right Place

An extra principal payment reduces your loan balance directly — but only if your servicer applies it correctly. If you simply send a larger check without instructions, some servicers apply the overage to next month's payment (prepaying interest you'd owe anyway) or hold it in suspense rather than reducing your principal. That mistake can erase most of the benefits.

To make sure every extra dollar reduces your balance:

1. Mark the payment “principal only.”Most online mortgage portals have a separate field or checkbox for additional principal. If you pay by check, write “apply to principal” in the memo line.
2. Keep your regular payment separate. Make your normal monthly payment first, then submit the extra principal payment on its own.
3. Verify on your next statement.Your statement should show the extra amount reducing your unpaid principal balance — not sitting as an “unapplied” or “prepaid” amount.

If you have a mortgage serviced by Total Mortgage, you can make a principal payment through your servicing account anytime.

Biweekly Mortgage Payments with Extra Payments

A biweekly payment plan means paying half your monthly mortgage payment every two weeks — 26 half-payments a year, the equivalent of 13 full payments instead of 12. On our example $300,000 loan at 7%, that one automatic extra payment per year saves $98,545 in interest and pays the loan off 6 years early.

To see your exact bi-weekly savings and full payment schedule, use our dedicated bi-weekly mortgage calculator .

Want to combine a biweekly schedule with additional extra payments? Model it right here: take your monthly principal-and-interest payment, divide it by 12, enter that as your monthly prepayment (about $166 on a $1,996 payment), then stack any additional monthly, yearly, or lump sum amounts on top. One caution — some third-party biweekly services charge setup or per-transaction fees for something you can do free yourself by adding 1/12 of your payment as extra principal each month.

One-Time Lump Sum Payments Toward Your Mortgage

A lump sum payment — from a tax refund, work bonus, inheritance, or home sale proceeds — immediately drops your principal balance, and every future interest charge is calculated on that lower amount.

Timing matters more than most homeowners realize. A $10,000 lump sum applied in year 2 of our example loan saves $54,363 in interest and shortens the loan by 2 years, 9 months. The same $10,000 applied in year 20 saves a fraction of that, because by then most of the loan's interest has already been paid. If you're deciding between investing a windfall or applying it to your mortgage, the earlier you are in your loan, the stronger the case for the mortgage.

Use the one-time extra payment field in the calculator above to test any lump sum amount and date against your own loan.

Extra Payments vs. Recasting vs. Refinancing

These three strategies are often confused, but they solve different problems:

Extra payments shorten your loan and reduce total interest, but your required monthly payment stays the same. Best when your goal is to be mortgage-free sooner and you can comfortably afford your current payment.

Mortgage recasting is when your lender re-amortizes your loan after a large principal payment, lowering your required monthly payment while keeping your original rate and payoff date. Most lenders charge a small fee ($150–$500) and require a minimum lump sum, often $5,000–$10,000. Best when you want lower monthly payments without refinancing.

Refinancing replaces your loan entirely — new rate, new term, new closing costs. Best when current rates are meaningfully lower than your existing rate, or you want to change your loan term or pull out equity. If lowering your monthly payment is the goal, start with our refinance calculator and check today's refinance rates.

How the Extra Mortgage Payment Calculator Works

The calculator uses standard amortization math to compute your current payoff schedule, then re-runs it with your extra payments applied to the principal each period.

Step 1 — Calculate your baseline monthly payment:

M = P × [r(1+r)ⁿ] ÷ [(1+r)ⁿ− 1]

• M = monthly principal & interest payment
• P = loan principal (e.g., $300,000)
• r = monthly interest rate = annual rate ÷ 12 (e.g., 7% ÷ 12 = 0.5833%)
• n = loan term in months (e.g., 30 years = 360 months)

On a $300,000 loan at 7% over 30 years: M = $300,000 × [0.005833 × 8.1165] ÷ [8.1165 − 1] = $1,995.91/month.

Step 2 — Find your new payoff date with extra payment E:

n_new= −ln(1 − P × r ÷ (M + E)) ÷ ln(1 + r)

Adding $100/month (E = $100) to our example: n_new= −ln(1 − 1,750 ÷ 2,095.91) ÷ ln(1.005833) = 310 months (25 years, 10 months) — 50 months sooner than the original 360.

Step 3 — Calculate interest saved:

Savings = (M × n_original) − ((M + E) × n_new)

The first term is total payments without extra; the second is total payments with extra. The difference is pure interest eliminated. For $100/month extra on our example: ($1,995.91 × 360) − ($2,095.91 × 310) = $718,527 − $649,732 = $68,795 saved.

For one-time lump sum payments, the calculator applies the lump sum to the principal balance on the payment date you specify, then re-amortizes the remaining balance over the remaining term at your original rate — giving you the exact new schedule from that point forward.

When Extra Mortgage Payments Don't Make Sense

Paying off your mortgage early isn't always the best use of your money. Consider holding off on extra payments if:

• You carry high-interest debt.Credit cards charging 20%+ cost you far more than your mortgage saves. Pay those down first — it's a guaranteed higher return.
• You don't have an emergency fund.Extra mortgage payments are illiquid: once paid, you can't easily get that money back without refinancing or a home equity loan. Keep 3–6 months of expenses accessible before accelerating your mortgage.
• You're skipping employer 401(k) matching. An employer match is an immediate 50–100% return. No mortgage prepayment competes with that.
• Your mortgage rate is very low. If you locked a rate well below what safe investments currently earn, the math may favor investing the difference instead. This is a personal decision that depends on your risk tolerance — paying down a mortgage is a guaranteed, tax-free return equal to your rate, which many homeowners value for the certainty alone.

When in doubt, talk to a loan officer about how prepayment fits your broader financial picture.