How to use it
- Find my payment: enter the loan amount, the yearly interest rate and the term in years (and months, for terms like 66 months).
- How much can I borrow?: enter the monthly payment you can manage instead; the calculator works out the largest loan it pays off over the term.
- Extra payments: add an amount every month, a one-time lump sum in a chosen payment, or both, to see the new payoff month and the interest saved.
- Schedule: switch between yearly totals and every payment, and download the whole schedule as a CSV file for a spreadsheet.
How it calculates
This is a fixed-rate, fully amortizing loan with monthly payments, the kind the Consumer Financial Protection Bureau describes for mortgages and auto loans: the payment stays the same, each month’s interest is charged on the balance still owed, and the rest of the payment reduces that balance, so early payments are mostly interest and late ones mostly principal. The level payment comes from the standard formula P × r ÷ (1 − (1 + r)−n) with r the yearly rate divided by 12, rounded to the cent. The schedule is then worked in whole cents: each month’s interest is the balance times the rate divided by 12, computed exactly and rounded to the nearest cent, and the scheduled last payment clears whatever the rounding left, which is why it can differ from the others by a few dollars on a 30-year loan.
Your lender’s figures can differ slightly if it charges interest by the day, rounds the payment up, or the first payment period is longer or shorter than a month. The rate to enter is the interest rate on the note; the APR also includes fees, so it is the number for comparing lenders rather than for working out the payment.
What we tested
On October 14, 2026 we checked the calculator’s engine against an independent Python implementation that uses exact fractions: 2,007 loans (random amounts, rates from 0% to 15%, terms from 6 to 480 months, with and without extra payments) and all 305,948 rows of their schedules agreed to the cent, including every payment, interest charge, balance and total, and for every loan the “how much can I borrow” answer had a payment no higher than the one entered. In Chromium: $25,000 at 7.25% for 5 years showed $497.98 a month; $300,000 at 6.5% for 30 years showed $1,896.20, $382,636.71 interest and a last payment in Oct 2056 (30 yearly and 360 monthly rows); $200 extra a month ended it after 277 payments, saving $103,450.19, and the downloaded CSV summed to the same interest with a final balance of 0.00; $500 a month at 7.25% for 5 years could borrow $25,101.20; a bad rate showed a message; the page fitted a 390 px phone with no errors.
| Loan | Monthly payment | Total interest | Last payment |
|---|---|---|---|
| $300,000 at 6.5%, 30 years | $1,896.20 | $382,636.71 | $1,900.91 |
| $25,000 at 7.25%, 5 years, +$100 a month | $497.98 | $3,902.92 (49 payments) | $199.88 |
| $10,000 at 0%, 3 years | $277.78 | $0.00 | $277.70 |
| $450,000 at 6.875%, 30 years, $10,000 once in payment 13 | $2,956.18 | $556,106.38 (337 payments) | $2,829.90 |
| $1,000 at 18.99%, 1 year | $92.15 | $105.84 | $92.19 |
Tips
- A shorter term costs more each month but far less overall: $300,000 at 6.5% is $1,896.20 a month over 30 years and $2,613.32 over 15, and the interest drops from $382,636.71 to $170,398.28.
- Extra payments do the most early, when the balance is largest. $200 a month extra on that 30-year loan ends it after 277 payments and saves $103,450.19.
- Before paying extra, ask the lender to apply it to principal and confirm there is no prepayment penalty.
Sources
Checked on .
Frequently Asked Questions
Built by Derek Giordano · Part of Ultimate Design Tools