Find out what extra principal does to the mortgage you already have. Enter today’s balance — or the original loan and how many payments you’ve made — then add an extra amount every month, once a year, or as a single lump sum. This extra mortgage payment calculator shows the new payoff date, how many payments you skip, the interest you save, and a year-by-year race between the two balances. It’s free, there’s no signup, and the math runs entirely in your browser.
How to use this calculator
- Describe the loan as it stands. Choose original loan and payments made if you know what you borrowed, the term, and how many monthly payments have cleared. Choose current balance to copy the principal balance and the principal-and-interest part of your monthly payment from your latest statement — the right choice if you’ve already paid extra, because it starts from where the loan really is.
- Enter the interest rate printed on your note or statement.
- Add any mix of extras: a fixed amount with every payment, a yearly amount that rides along with every 12th payment (a bonus or a tax refund, say), and a one-time lump sum with the payment number it goes with — 1 means your next payment.
- Read the comparison. Interest saved leads; below it sit both payoff dates, the interest left on each path, and a table of year-end balances.
The calculator opens with an example loan — $325,000 at 6% for 30 years, 60 payments in, with $100 a month extra. Replace every number with your own; the address bar updates as you type, so you can bookmark or share a scenario.
Why extra principal early saves the most
Interest each month is the balance times one-twelfth of the annual rate, so a dollar that leaves the balance stops costing interest for every month the loan has left. Early on, that is a lot of months, and most of each payment is still interest: in the example, payment 61 is $1,948.54, and $1,512.13 of it is interest. The same money buys less the later it arrives. Here is a one-time $10,000 applied at different points of that same $325,000, 6%, 30-year loan:
| $10,000 paid with | Interest saved | Payments skipped |
|---|---|---|
| Payment 1 | $45,880.32 | 28 |
| Payment 61 | $32,176.33 | 21 |
| Payment 121 | $21,697.21 | 16 |
| Payment 241 | $7,739.32 | 9 |
| Payment 301 | $3,227.59 | 6 |
Paid in year 26, the lump sum saves about a fourteenth of what it saves on day one. The same arithmetic makes a steady extra surprisingly strong: on the example loan, $100 a month adds up to $26,800 of extra principal and saves $34,184.18 of interest, about $1.28 for every extra dollar. To see which month each dollar lands in, the amortization schedule calculator lays out the full month-by-month split for any loan.
Check for a prepayment penalty first
A prepayment penalty is a fee some lenders charge if you pay off all or part of a mortgage early. The Consumer Financial Protection Bureau says it typically applies when the whole balance is paid off — by selling or refinancing — within a set number of years, usually three or five, and does not normally apply to extra principal paid in small chunks; it still suggests confirming with your lender. Whether your loan has one must have been disclosed in your loan documents, so look at the note and any page titled “Addendum to the Note”.
Regulation Z’s minimum standards for loans secured by a dwelling (12 CFR 1026.43, the rule that also requires lenders to check your ability to repay — home equity lines of credit are excluded) took effect on January 10, 2014. For covered home loans closed on or after that date, a penalty is allowed only on a qualified mortgage whose APR cannot rise after closing and that is not a higher-priced loan. It cannot apply after the first three years and is capped at 2% of the amount prepaid in years one and two and 1% in year three. Many states add their own limits. If a penalty applies, weigh it against the interest saved above before sending a large lump sum.
Limits and tips
- Fixed rate only. Both paths assume today’s rate for the rest of the loan. If yours is adjustable, each reset changes the payment and the savings.
- Original-loan mode assumes an on-schedule loan. It rebuilds today’s balance as if every payment so far was exactly the scheduled amount. If you’ve already paid extra, your real balance is lower and the loan ends sooner than that schedule shows, so the savings it reports would be too high — use current-balance mode with the figures from your latest statement.
- Principal and interest only. Escrow for property taxes and insurance is not part of the math, so compare results with the principal-and-interest line of your statement.
- Dates are estimates. Payoff months assume your next payment is due next month.
- Other ways to finish sooner. Refinancing into a shorter term is another route; the refinance break-even calculator shows how long closing costs take to pay back, and the mortgage payment calculator prices a new 15- or 20-year payment.
- Only the mortgage is compared. The calculator doesn’t weigh other uses of the same money, such as higher-rate debt — the credit card payoff calculator shows what a card balance costs.
Privacy
The calculation runs entirely in your browser, and your numbers stay there. They’re kept in the page address (the part after the “?”) so you can bookmark or share a result; typing sends nothing to us, and analytics never sees them — Google Analytics receives page addresses without that part. Our privacy policy has the details.