Accelerated Payment Calculator
Paying even a little extra on a loan shortens its life and cuts the total interest, but the size of the win is hard to feel until you see the numbers. This calculator shows both acceleration strategies side by side: adding a fixed extra amount to each monthly payment, and the accelerated biweekly trick of paying half your monthly payment every two weeks (26 half-payments a year equals 13 full ones).
For each strategy you get the new payoff time, the total paid, and the two numbers that matter most: interest saved and time saved versus the standard schedule.
Extra monthly payments or accelerated biweekly: payoff date, interest saved, time saved.
Principal and interest only. Taxes, insurance, PMI, lender fees, and prepayment penalties are not included. Confirm with your servicer that extra payments are applied to principal.
Worked example: $300,000 mortgage, 6.5%, 30 years, +$200 a month
Enter loan $300,000, rate 6.5%, term 30 years, extra $200. Standard payment: $1,896.20 a month. With the extra: $2,096.20. Payoff in 277 months (23.1 years) instead of 360. Total paid $579,183 versus $682,633 standard: $103,450 interest saved, 6.9 years early. Verified against the calculator.
Biweekly example: the same loan, no extra cash needed
Switch to the accelerated biweekly tab with the same loan. Paying $948.10 every two weeks (half the monthly payment, 26 times a year) pays the loan off in 24.2 years, saving $88,121 in interest and 5.8 years. The trick is the 13th monthly payment each year, which goes straight to principal.
The formulas, stated plainly
Standard payment = principal x monthly rate / (1 – (1 + monthly rate)^-months).
With extra: months to payoff = ln(payment / (payment – principal x monthly rate)) / ln(1 + monthly rate).
Accelerated biweekly: half the monthly payment every 14 days at annual rate / 26, simulated period by period until the balance clears. Interest saved = standard total interest – accelerated total interest.
When extra payments are the wrong move
Acceleration is not always smart. If your loan charges a prepayment penalty, the fee can eat the saving; check your agreement first. Money put toward a 6.5% mortgage earns you 6.5% after tax, but credit-card debt at 20%+ should die first, and an emergency fund comes before optional principal payments. If your rate is under 3%, investing the extra often beats prepaying. Run the numbers, then decide.
What competing calculators miss
The bank calculators on this keyword show the biweekly trick but never the plain extra-monthly-payment strategy, and most never headline the two numbers you came for: interest saved and time saved. This calculator runs both strategies, shows the full comparison, and handles 0% loans, where the previous version of this page returned a blank NaN.
Frequently asked questions
How much can I save by paying extra on my mortgage?
On a $300,000 loan at 6.5% over 30 years, $200 extra a month saves about $103,450 in interest and 6.9 years.
How do accelerated biweekly payments work?
You pay half your monthly payment every two weeks: 26 half-payments a year equals 13 full monthly payments. The extra payment goes to principal.
Is it better to pay extra monthly or switch to biweekly?
A fixed extra payment usually wins if you can afford it ($200/month beats the biweekly trick on the example loan). Biweekly wins on discipline: the extra payment happens automatically.
Do extra payments go toward principal?
Only if your servicer applies them that way. Confirm in writing; some lenders hold extra as a future payment instead.
Are there penalties for paying off a loan early?
Some mortgages and auto loans charge prepayment penalties. Check your loan agreement before accelerating.
What if my interest rate is 0%?
The calculator handles it: payment is simply principal divided by months, and extra payments shorten the term directly.