Extra Payment Calculator
Find out what paying a little extra each month actually does to your mortgage: how many years it removes, and how much interest it saves you.
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What overpaying actually does
An extra payment does not reduce your monthly instalment. Your lender keeps charging the same amount, but every extra dollar goes straight against the principal, so the balance it charges interest on is permanently smaller. The result is that the loan finishes early, and the interest you never accrue is money you keep. Nothing about the rate changes; what changes is how long you are exposed to it.
The effect is far larger than most people expect, because you are removing interest from every remaining month rather than just from the current one. Adding 200 dollars a month to a 300,000 dollar loan at 6.5 percent clears it in about 23 years and one month instead of 30, and cuts total interest from 382,633 dollars to 279,185 dollars. That is 103,449 dollars saved for an extra 200 dollars a month, and the money is not lost: it all went into your own equity.
Timing matters enormously. An extra 200 dollars paid in year one removes interest from all 360 months that follow it. The same 200 dollars paid in year 25 removes interest from only the final few years. This is why overpaying early feels disproportionately powerful, and why the calculator shows a much bigger saving the earlier you start.
One practical caution before you commit the money. Check whether your loan has a prepayment penalty, which is uncommon on standard US mortgages but does exist. Also make sure the extra is applied to principal specifically, not held as a credit against next month's payment. Lenders do this differently and you usually have to say which you want.
How the saving is calculated
The calculator runs the loan twice, once at the contractual payment and once with your extra amount added, then compares the totals.
| Symbol | Meaning |
|---|---|
A |
The scheduled principal and interest payment |
E |
Your extra principal payment each period |
n |
Contractual number of payments in the original term |
Σ |
Sum of the interest actually charged over the shorter life of the loan |
The extra payment is applied after that period's interest is covered, which is the standard way lenders apply additional principal. The schedule stops as soon as the balance reaches zero, so the reported term reflects the real payoff.
Worked example: 200 dollars extra per month
A 300,000 dollar loan at 6.5 percent over 30 years, with and without an extra 200 dollars a month.
| Metric | Without extra | With $200 extra |
|---|---|---|
| Monthly payment | $1,896.20 | $2,096.20 |
| Time to pay off | 30 years | 23 years 1 month |
| Number of payments | 360 | 277 |
| Total interest | $382,633.47 | $279,184.67 |
| Total paid | $682,633.47 | $579,184.67 |
| Interest saved | — | $103,448.79 |
| Time saved | — | 6 years 11 months |
You pay an extra 55,400 dollars over the life of the loan and save 103,449 dollars in interest, finishing almost seven years early. The 55,400 dollars is not a cost: it reduced your own debt. The genuine saving is the interest you were never charged.
Estimates only. Your lender's figures may differ because of fees, escrow and rounding.
Making extra payments work harder
Round the payment up, permanently
Increasing a 1,896.20 dollar payment to 2,000 dollars is 103.80 dollars a month, which most budgets absorb without noticing, and it is enough to remove several years from a 30-year term. Set it up as a standing instruction so it happens without a decision.
Send one lump sum a year instead
If your income arrives in bonuses or irregular payments, a single annual overpayment achieves much of the same result as a monthly top-up. What matters is the total paid against principal each year, not its frequency.
Clear high-interest debt first
Overpaying a 6.5 percent mortgage while carrying a credit card at 24.99 percent is the wrong order. Every dollar sent to the card earns a guaranteed 24.99 percent; every dollar sent to the mortgage earns 6.5 percent. Clear the expensive debt, then attack the mortgage.
Keep an emergency fund before you overpay
Money paid into a mortgage is very hard to get back out; a lender will not return it because you lost your job. Keep three to six months of expenses accessible, and overpay only with what is genuinely surplus.
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Frequently asked questions
How much does an extra 200 dollars a month save?
On a 300,000 dollar loan at 6.5 percent over 30 years, an extra 200 dollars a month saves about 103,449 dollars in interest and pays the loan off roughly seven years early. The exact figure depends on your rate, balance and how early in the term you start.
Will my monthly payment go down if I pay extra?
No. On a standard fixed-rate mortgage the instalment stays the same and the loan simply ends sooner. Some lenders will recast the loan on request, which does lower the payment by spreading the remaining balance over the original term, but you usually have to ask and it can carry a fee.
Is it better to overpay the mortgage or invest the money?
Overpaying gives a guaranteed return equal to your mortgage rate, which is attractive when rates are high. Investing has historically returned more over long periods but with real risk and no guarantee. Overpaying also reduces your fixed monthly obligation over time, which is a form of security that a portfolio does not provide.
When is the best time to start overpaying?
Immediately, if you have the money and a solid emergency fund. The saving comes from removing interest from every remaining month, so a payment made in year one is worth far more than the same payment made in year twenty. There is no penalty for starting early.
Are there prepayment penalties?
Most standard US mortgages have none, but some loans, particularly certain government-backed and subprime products, charge a fee if you pay off or substantially overpay within the first few years. Check your loan documents before committing to a large overpayment.