How to use the mortgage extra payment calculator
Start from a recent mortgage statement. Enter the unpaid principal balance, your interest rate and how many payments are left. Use today's balance, not the original loan amount or your home's value, and the note rate rather than the APR.
Then add the extra principal you're thinking about. You can set when a monthly extra starts, add a yearly amount at any point in the year, and drop in a one-time lump sum on a specific payment.
- Enter your current principal balance, interest rate, and the years and months left.
- Add an extra monthly amount and the payment number it starts with.
- Add a yearly extra and pick which payment in each 12 it lands on.
- Add any one-time lump sum and the payment number it goes with.
- Set a target payoff time to see the monthly extra you'd need.
- Press Calculate and compare payoff time, interest saved and the yearly balance table.
Example: $280,000 with $200 extra a month
Say you owe $280,000 at a fixed 6.5% with 30 years left. Your principal and interest payment is $1,769.79. If you never pay extra, you'll pay $357,124.57 in interest over the remaining term.
Add $200 a month to principal from the first payment and the loan is gone in 273 payments, or 22 years and 9 months. Interest falls to $255,841.38. That's $101,283.19 saved for $54,400 of extra payments. Your required payment doesn't change, and the last payment is only $58.37.
| Plan | Monthly P&I paid | Paid off in | Interest left to pay |
|---|---|---|---|
| No extra | $1,769.79 | 30 years | $357,124.57 |
| $200 extra from payment 1 | $1,969.79 | 22 years, 9 months | $255,841.38 |
| Difference | +$200.00 | 7 years, 3 months sooner | $101,283.19 less |
How the extra payment math works
The calculator first works out your required payment from the balance, rate and payments left. Then it runs two schedules month by month: one with no extra and one with your extra payments on the dates you chose.
Each month, interest is charged on the opening balance. The required payment covers that interest plus some principal, and any extra goes straight to principal. Because next month's interest starts from a lower balance, the gap between the two schedules grows over time.
Required P&I = P x r / (1 - (1 + r)^(-n))r = annual interest rate / 100 / 12Interest this month = opening balance x rNew balance = opening balance - (required P&I - interest) - extra principalInterest saved = standard remaining interest - interest with extras
How much do $100, $200 or $300 extra save?
More extra saves more, but not in a straight line. On the example loan, $100 a month saves about $60,213, while tripling it to $300 saves about $131,512. Pick an amount you can keep paying alongside your full required payment.
In the first year, the savings look tiny. With $200 extra, your balance is $2,472.81 ahead after 12 payments, but you've only avoided $72.81 of interest so far. Extra principal pays down the loan right away. The interest savings show up later, every month for the rest of the loan.
| Monthly extra | Total P&I a month | Paid off in | Interest saved |
|---|---|---|---|
| $0 | $1,769.79 | 30 years | $0 |
| $100 | $1,869.79 | 25 years, 9 months | $60,213.09 |
| $200 | $1,969.79 | 22 years, 9 months | $101,283.19 |
| $300 | $2,069.79 | 20 years, 5 months | $131,511.88 |
One extra mortgage payment per year
Making one extra full payment each year is a popular way to pay off a mortgage early. On the example, adding $1,769.79 with every 12th payment pays the loan off in 24 years and 4 months and saves about $78,386. Splitting that same amount into $147.48 a month does slightly better, about $81,438, because the money starts working sooner.
This is the idea behind biweekly plans, which make 26 half-payments a year. The calculator doesn't model biweekly timing. Some servicers hold partial payments until they add up to a full one, and some third-party programs charge fees, so ask before you sign up.
| Strategy | Paid off in | Interest left to pay | Interest saved |
|---|---|---|---|
| $1,769.79 once a year | 24 years, 4 months | $278,739.03 | $78,385.55 |
| $147.48 a month | 24 years, 2 months | $275,686.41 | $81,438.16 |
| $1,200 once a year | 25 years, 11 months | $299,262.14 | $57,862.42 |
| $10,000 lump sum with payment 12 | 27 years, 3 months | $307,240.92 | $49,883.64 |
Early mortgage payoff: why starting sooner helps
The start field lets you model a plan that begins later, for example when a car loan ends or you get a raise. Every month you wait, the higher balance keeps collecting interest. The same $200 a month saves about $101,283 if it starts now, about $93,438 if it starts with payment 13 and about $65,761 if it starts with payment 61.
To pay off by a set date, use the target fields. With no other extras, being done in 20 years takes about $317.81 extra a month, for $2,087.60 of principal and interest in total.
| First extra with | Paid off in | Interest saved | Balance ahead after year 5 |
|---|---|---|---|
| Payment 1 | 22 years, 9 months | $101,283.19 | $14,134.79 |
| Payment 13 | 23 years, 2 months | $93,437.66 | $10,929.99 |
| Payment 61 | 24 years, 9 months | $65,760.71 | $0.00 |
Limits and when to double-check
The calculator models a fixed-rate loan with monthly interest and assumes every extra dollar goes to principal on the payment you picked. Real servicers post on exact dates and may treat extra money differently. The payment shown is principal and interest only, so property taxes, insurance and other escrow items aren't included.
Extra principal usually doesn't lower your required payment. A recast can, but it's a separate process your servicer has to approve. Adjustable rates, interest-only periods and balloon loans aren't modeled.
- Tell your servicer the extra is for principal, and check your next statement.
- Read your note for a prepayment penalty. The CFPB says small extra payments don't normally trigger one.
- Keep paying the full required amount, including escrow, every month.
- Ask for a dated payoff quote before a final payment, sale or refinance.
Sources
These official and agency sources cover extra principal, prepayment penalties, payoff amounts and recasting.