Mortgage payoff & extra payment calculator
See what a little more each month could change.
- Formula and assumptions shown
- Table and CSV export
- Runs in your browser
Inputs
Result
Assumptions used
Enter your numbers to see an estimate.
Assumptions and methodology
Balance over time
Monthly viewChart data will appear here as a text summary.
How it works
This tool models two schedules from the same current balance: the regular payment and the regular payment plus a fixed extra amount. It reports the difference in payoff months, total interest, and total paid.
The extra amount is applied in every modeled month starting with the first payment. The model does not include biweekly payments, annual extras, or lump-sum payments, so those real-world strategies need separate lender-specific calculations.
Extra payments have the largest effect early, when the balance and the interest charged on it are highest. The same monthly extra started later in a loan saves fewer months and less interest, so if you are partway through, enter your current balance and remaining term rather than the original loan. Weigh the interest saved against other uses of the money, such as higher-rate debt or emergency savings.
Assumptions
- The starting amount is your current balance and the term is the remaining modeled term, not necessarily the original contract term.
- The extra payment is fixed, monthly, and begins with the first modeled payment; no biweekly or lump-sum payments are included.
- Extra payments are treated as principal-directed in the model. Your lender may apply overpayments to fees, interest, or future installments instead.
- The estimate uses monthly nominal-rate interest and excludes prepayment penalties, fees, rate changes, and daily-interest conventions.
Worked example
$300,000 at 6.5% with $200 extra
Over 30 years, the regular payment is $1,896.20 and modeled interest is $382,633.47 across 360 months. Adding $200 a month from the first payment pays the loan off in 277 months (23 years 1 month), 83 months (6 years 11 months) sooner, with $279,184.67 of interest: an estimated $103,448.79 less.
Step by step
- Find the regular payment. The monthly rate is 6.5% ÷ 12 = 0.5417% over 360 months. The standard payment formula gives $1,896.20 of principal and interest.
- Apply the first payment. Month 1 interest is $300,000 × 0.5417% = $1,625.00. The regular payment would reduce principal by $1,896.20 − $1,625.00 = $271.20; adding $200 raises that to $471.20, so the balance falls to $299,528.80.
- Let the lower balance compound. Each month starts from a slightly lower balance, so it is charged slightly less interest, and more of the fixed $2,096.20 goes to principal the following month.
- Find the payoff month. Repeating this month by month, the balance reaches zero in month 277 (23 years 1 month) instead of month 360: 83 months sooner. The last payment is a partial $632.35.
- Compare interest and total paid. Interest on the regular schedule totals $382,633.47; with the extra payment it totals $279,184.67, a difference of $103,448.79. Total paid falls from $682,633.47 to $579,184.67.
How to read your result
The headline is the new payoff time, and the line under it states how much sooner that is and how much less interest is paid than on the regular schedule. The secondary figures repeat the regular payment, the extra amount, the interest saved, and the time saved. The chart draws two balance lines, one with the extra payment and one without, so the gap between them shows how far ahead the extra payments put you in any month.
The interest saved is measured over the full remaining term. It builds gradually: if the loan is sold, refinanced, or paid off early for another reason, only the part of the savings accrued up to that point is realized. The schedule table shows the accelerated plan month by month and can be downloaded.
The regular payment here is principal and interest only. Property tax, insurance, and mortgage insurance in an escrow payment are not affected by extra principal and are not included. The required monthly payment also does not fall; the loan simply ends sooner.
What changes the result most
- Size of the extra payment
- On this $300,000 loan, an extra $100 a month saves 48 months and $60,994.79 of interest; $200 saves 83 months and $103,448.79; $500 saves 150 months and $179,759.08; $1,000 saves 207 months and $241,162.07. Each added dollar still saves interest, but each one shortens the loan by fewer months.
- When the extra payments start
- After 10 years of regular payments the balance is $254,328.38. Adding $200 a month from that point, with 20 years left, saves 41 months and $39,657.94 of interest, less than half the months and about 38% of the interest saved by starting at the beginning.
- Interest rate
- The same $200 on a $300,000, 30-year loan saves 77 months and $69,210.37 at 5%, and 88 months and $130,781.04 at 7.5%. Higher rates make each dollar of prepaid principal avoid more interest.
Questions
Can I use the original loan amount?
Use the current outstanding balance and remaining term when you are already partway through a loan. Using the original figures describes a new loan scenario instead.
Will my lender apply the extra payment to principal?
Not always. Some servicers require a principal-only instruction, and some may credit an overpayment toward a future bill. Confirm the payment rules before relying on the modeled savings.
Does paying extra always make sense?
It can reduce interest in a fixed-rate model, but compare the benefit with emergency savings, other debt rates, fees, and your contract before changing payments.
How much does paying extra on a mortgage save?
It depends on the balance, rate, remaining term, and the size of the extra payment. In this page’s example, $200 a month on a $300,000 loan at 6.5% saves $103,448.79 of interest and 83 months; $100 a month saves $60,994.79 and 48 months. Enter the current balance and remaining term to see your own figures.
Are biweekly mortgage payments the same as paying extra?
Paying half the monthly payment every two weeks produces 26 half-payments, or 13 full payments a year instead of 12, if the servicer applies each half-payment when it arrives. That is roughly the same as adding one-twelfth of the payment each month: $1,896.20 ÷ 12 = $158.02, which this model shows saving about 70 months on the example loan. Some servicers hold partial payments until a full payment accumulates, and some third-party biweekly programs charge fees.
Do extra payments lower my monthly payment?
Not on a standard fixed-rate loan. The required payment stays the same and the loan is paid off sooner. Some lenders will recast the loan after a large principal payment, recalculating a lower payment over the remaining term, usually for a fee; the mortgage recast calculator models that option.
More in Loans & debt
Sources
These references explain the concepts behind the calculation. They do not endorse this site. Estimates leave out any cost or condition you did not enter.