How to use the mortgage payoff calculator
- Enter your loan details: current balance, interest rate and remaining term in years.
- Add extra payments: an extra monthly amount, a one-time lump sum with the payment number it is paid with, or tick biweekly half-payments.
- Read the results: new payoff length, time saved and interest saved. Enter a start month to also see the month each schedule ends.
- Compare scenarios: change one extra-payment field at a time to see which strategy saves the most.
How the payoff calculation works
The mortgage payoff calculator first computes the standard monthly payment with the amortization formula: P * r / (1 - (1 + r)^(-n)), where P is the loan amount, r is the monthly rate (annual rate / 12 / 100) and n is the number of monthly payments. For $300,000 at 6.5% over 30 years, r = 0.065 / 12 = 0.0054167 and n = 360, which gives a payment of $1,896.20. The payment is rounded to the cent, as a lender does.
It then walks through the loan one payment at a time. Each month the interest on the remaining balance is rounded to the cent, the payment plus any extra money is applied, and the rest reduces principal. The schedule stops when the balance reaches zero, and the last payment is whatever is left. That is why the interest total for the standard loan is $382,636.71, a few dollars more than 360 payments of $1,896.20 minus the loan amount.
In biweekly mode there are 26 payments a year, each half of the monthly payment, with interest charged at the annual rate divided by 26. An extra monthly amount is spread over those payments so the extra money per year stays 12 times what you entered. A lump sum is added to the payment you choose by number.
Extra payment strategies compared
Three common ways to pay off a mortgage faster:
- Extra monthly: a fixed amount added to every payment. Predictable and easy to budget.
- Biweekly half-payments: half the monthly amount every two weeks. Twenty-six half-payments equal 13 full payments a year, so you pay the equivalent of one extra monthly payment annually, spread out.
- Lump sum: a one-time windfall such as a bonus or tax refund applied to principal. The earlier in the loan, the more interest it saves.
Combining them adds up. On $300,000 at 6.5% over 30 years, $100 extra a month plus a $20,000 lump sum at payment 60 pays the loan off in 23 years 0 months instead of 30 years and saves $111,757 in interest.
Interest savings reference table
Results for a $300,000, 30-year mortgage at 6.5%, with no start month. The standard schedule costs $382,636.71 in interest. Interest saved is rounded to the nearest dollar.
| Strategy | New payoff | Time saved | Interest saved |
|---|---|---|---|
| Standard, no extra | 30 yr 0 mo | 0 | $0 |
| $100 extra monthly | 26 yr 0 mo | 4 yr 0 mo | $60,996 |
| $200 extra monthly | 23 yr 1 mo | 6 yr 11 mo | $103,450 |
| $500 extra monthly | 17 yr 6 mo | 12 yr 6 mo | $179,762 |
| Biweekly only | 24 yr 2 mo | 5 yr 10 mo | $88,123 |
| Biweekly plus $100 monthly | 21 yr 8 mo | 8 yr 4 mo | $123,649 |
| $20,000 lump sum at payment 60 | 26 yr 2 mo | 3 yr 10 mo | $69,076 |
Exact figures depend on how your servicer applies extra payments and when they post, so treat the table as a guide to the size of each effect, not a quote.
Common mistakes and edge cases
- Confusing APR with the note rate: use the note rate, the rate your payment is based on, not the APR that folds in fees.
- Using the original term instead of the remaining term: if you are 5 years into a 30-year loan, enter your current balance and 25 years.
- Forgetting escrow: your real payment includes taxes and insurance. This calculator shows principal and interest only.
- Biweekly versus twice a month: 24 half-payments a year (semi-monthly) equal 12 full payments, so they do not create the extra annual payment. True biweekly is 26 payments.
- Prepayment penalties: uncommon on modern mortgages, but check your note. This tool assumes none.
- Extra payments must go to principal: some servicers hold extra money as an early payment unless you mark it as principal-only.
When to refinance instead of prepaying
If market rates have fallen well below your rate, refinancing can save more than prepaying. Compare the closing costs of the new loan with the monthly saving: divide the costs by the saving to get the break-even point in months, and only refinance if you expect to keep the loan longer than that. This mortgage payoff calculator can model the new loan too: enter the new balance, rate and term along with your planned extra payments.
Results are estimates based on the numbers you enter and are not financial advice. Confirm the details of any extra-payment plan with your lender or servicer.
Worked examples
| Example | Input | Result |
|---|---|---|
| Standard 30-year with $200 extra monthly | Loan amount: 300000; Interest rate (%): 6.5; Loan term (years): 30; Extra monthly payment: 200 | Monthly payment: 1,896.20; Original payoff: 30 years 0 months; Total interest (original): 382,636.71; New payoff: 23 years 1 month; Time saved: 6 years 11 months; Interest saved: 103,450.19; Total interest (new): 279,186.52 |
| Biweekly payments on a $400k loan | Loan amount: 400000; Interest rate (%): 5.75; Loan term (years): 30; Biweekly half-payments: yes | Monthly payment: 2,334.29; Biweekly payment: 1,167.15; Original payoff: 30 years 0 months; Total interest (original): 440,345.85; New payoff: 24 years 9 months; Time saved: 5 years 3 months; Interest saved: 90,887.87; Total interest (new): 349,457.98 |
| Lump sum at payment 60 plus $100 monthly | Loan amount: 250000; Interest rate (%): 7; Loan term (years): 30; Extra monthly payment: 100; One-time lump sum: 20000; Lump sum at month: 60 | Monthly payment: 1,663.26; Original payoff: 30 years 0 months; Total interest (original): 348,769.07; New payoff: 21 years 9 months; Time saved: 8 years 3 months; Interest saved: 119,211.87; Total interest (new): 229,557.20 |
| Near payoff: 5 years left, $500 extra | Loan amount: 80000; Interest rate (%): 4.5; Loan term (years): 5; Extra monthly payment: 500 | Monthly payment: 1,491.44; Original payoff: 5 years 0 months; Total interest (original): 9,486.46; New payoff: 3 years 8 months; Time saved: 1 year 4 months; Interest saved: 2,614.35; Total interest (new): 6,872.11 |
| With payoff dates (first payment 2026-01) | Loan amount: 300000; Interest rate (%): 6.5; Loan term (years): 30; Start month: 2026-01; Extra monthly payment: 200 | Monthly payment: 1,896.20; Original payoff: 30 years 0 months; Total interest (original): 382,636.71; New payoff: 23 years 1 month; Time saved: 6 years 11 months; Interest saved: 103,450.19; Total interest (new): 279,186.52; Original payoff date: December 2055; New payoff date: January 2049 |
FAQ
How much interest will I save by paying $100 extra per month?
On a $300,000 loan at 6.5% for 30 years, $100 extra a month saves about $60,996 in interest and shortens the loan by 4 years 0 months. Your savings depend on your balance, rate and remaining term.
Is biweekly better than one extra payment a year?
In this calculator both routes pay the $300,000 loan off in 24 years 2 months, but biweekly half-payments save $88,123 in interest against $87,259 for an extra 158.02 a month (one extra payment a year). The difference, about $864, comes from the money arriving earlier. Your servicer may not accept biweekly payments, and some charge a fee to set them up.
Should I use my current balance or the original loan amount?
Use your current principal balance and the remaining term. If you are 7 years into a 30-year mortgage, enter your balance and 23 years.
Does this include property taxes and insurance?
No. It shows principal and interest only. Your real monthly payment also covers escrow for taxes and insurance, which extra principal payments do not change.
Can I apply a lump sum at any month?
Yes. Enter the amount and the payment number it is paid with, where 1 is the first payment. It is added to that month's payment, after the interest for the month is charged.
What if my lender does not accept biweekly payments?
Add one-twelfth of your monthly payment to each monthly payment for a similar effect, or make one extra payment a year. Ask your servicer how they want extra money labeled.
How accurate is the payoff estimate?
The schedule is exact for the inputs given, using monthly interest rounded to the cent. Real loans can differ by posting dates, fees, escrow changes and how a servicer applies extra payments, so treat the result as an estimate.