Is it worth overpaying your mortgage by $100 a month?

What does $100 a month actually save?

Unless a section says otherwise, every figure below runs one scenario: a $264,162 balance with a full 30 years still to go, at 6.58%. That balance is the 2026 US average; most people carrying it are some years into their loan rather than at the start, and with fewer years left there is less interest to cancel, so the savings shrink — the section on starting later shows by how much.

On that balance, the scheduled payment covering principal and interest is $1,683.61, and over 360 payments the interest comes to $341,936. That is 1.29 times the balance itself — you pay more in interest than you currently owe.

Add $100 to every payment and the interest falls to $281,164. The difference, $60,772, is interest that simply never gets charged, because the balance it would have been charged on is gone early.

Look down that last column. Sending more extra saves more money in total, but each dollar comes back a little smaller — $2.08 at $25 a month, $1.82 at $300. Nothing is going wrong; you are running out of loan. The savings come from interest you avoid, and once the balance is gone there is no more interest left to avoid.

Your required payment will not go down

This is the single most common surprise, so it is worth being blunt about. Your required payment was fixed when the loan was written, based on the original balance, rate, and term. Prepaying does not re-run that calculation. Send $100 extra in March and April's principal-and-interest bill is still $1,683.61, plus whatever your escrow costs — escrow being the separate slice your servicer collects to pay your property tax and homeowners insurance for you.

What you bought is a shorter loan, not a cheaper month. If your goal was breathing room in the monthly budget, overpaying does the opposite in the short run — it takes $100 more out of every month for years before anything changes.

There is one way prepaying really does shrink the bill, and it applies to anyone who put down less than 20%. If you are paying private mortgage insurance — often $100 to $330 a month, depending on your credit and down payment — you can ask your lender to cancel it once your balance reaches 80% of the home's original value. Extra principal gets you to that line sooner. On our $264,162 balance with 10% down, $100 a month moves the 80% line up from month 96 to month 72, so two years of premiums never get charged: about $3,600 at $150 a month.

Do not count on the other cancellation date moving, though. PMI also terminates automatically at 78%, but by law that date is fixed to your original amortization schedule regardless of what you actually owe, so prepaying does not pull it forward at all. The request at 80% is the one you can accelerate, and it is worth calling your servicer to ask exactly what balance triggers it.

Keep the size of this in proportion. If your goal is a smaller monthly bill, killing PMI early is the biggest lever prepaying gives you — it is the only part that touches what you owe each month. But as a reason to prepay at all it is minor next to the interest: $3,600 of premiums against $60,772 of interest, a factor of about 17.

Beyond that, the tool that lowers a payment is a recast: the lender re-amortizes what you still owe over the remaining term, so the payment drops while the rate and payoff date stay put. Among servicers that offer it, expect a $150 to $500 fee and a required lump sum of $5,000 to $10,000 first; FHA, VA, and USDA loans are generally not eligible, and some servicers do not recast at all. Escrow is not re-figured either way, so the tax-and-insurance slice keeps moving on its own schedule.

The same $100 is worth wildly different amounts

"You could save thousands" is the standard line, and it is useless, because the number depends almost entirely on the rate you are cancelling. What you are really buying with a prepayment is the interest that rate was going to charge — so a high rate makes the same $100 far more valuable.

From 3% to 8% the payoff on an identical $100 swings by a factor of 4.5. If you locked a 3% loan in 2021, prepaying it is one of the weakest uses of a spare $100 you have. At 8% it is one of the strongest. Anyone quoting a single savings figure without asking your rate is guessing.

Starting later costs you most of the benefit

Interest is charged on the balance, and the balance is at its biggest at the start. That makes early prepayments the ones that cancel the most interest — and it means waiting is expensive in a way that is easy to miss.

On that same loan, ten years in, the balance is down to $224,394 with twenty years to run. Start the $100 habit at that point and it cancels $22,216 and pulls the payoff in by 25 payments. Same $100 a month, same rate, same discipline — about 37% of what it would have done from month one.

What if you saved the $100 instead?

Here is the cleanest way to think about it. A dollar of balance you erase is a dollar that stops being charged 6.58% a year for the rest of the loan. So overpaying returns your mortgage rate, guaranteed, and the saving is not itself taxed. That is the number any alternative has to beat.

One correction to that if you itemize your deductions and write off mortgage interest: killing the interest kills the deduction too, so your real return is the rate minus your tax bracket — about 5.13% instead of 6.58% in the 22% bracket. Most filers take the standard deduction and get no such write-off, in which case the full rate stands.

In July 2026 the strongest high-yield savings accounts pay around 4.20% APY and the FDIC average across all savings accounts is 0.38%. Savings interest is taxable, so in the 22% bracket — meaning the rate charged on your next dollar of income — that 4.20% nets about 3.28%. Against a 6.58% mortgage, the mortgage wins.

One honest caveat before you lean on those totals. The $60,772 is a running total of interest avoided over 25 years, while the savings figures are a balance sitting in an account at the end — money you could withdraw. They are not the same kind of number, and the mortgage column flatters itself by not discounting future dollars. The gap here is wide enough to survive that, but at rates closer together it would not be, which is why the rate comparison below is the reliable test rather than the dollar totals.

That test is per dollar, not per total: compare your mortgage rate to what the alternative nets you after tax. If you take the standard deduction, the line is the 3.28% the account keeps rather than its 4.20% headline — about 3.23% once converted to the monthly compounding a mortgage uses. Below roughly that rate, holding the cash pays you more than prepaying saves you, and prepaying becomes the worse deal even though it still "saves interest."

If you itemize and deduct your mortgage interest, the line moves up rather than down, which is easy to get backwards. Both sides are then taxed at the same rate — the deduction you lose and the savings interest you would owe tax on — so the tax cancels out and you compare the headline numbers directly. That puts your crossover at the account's full 4.20% APY, or about 4.12% in mortgage terms. A 4% mortgage is worth prepaying if you take the standard deduction and roughly a wash if you itemize.

Two things that pay more than 6.58%

Before the mortgage gets your spare $100, two claims beat it outright. A carried credit-card balance typically charges well over 20%, so clearing it is worth three times what prepaying the house is. And an employer 401(k) match you are not fully claiming is an immediate 50% or 100% on the money, which no mortgage rate comes near.

There is also a reason to hold the $100 that has nothing to do with rates. Money you send to the mortgage is gone into the house. Getting it back means selling, refinancing, or borrowing against the equity — a home equity loan, or a HELOC, which is a credit line secured by your house that you draw on as needed. Every option except selling depends on your income and credit at the time you ask, which makes them hardest to get in exactly the situation where you would need them, and selling is not much of an emergency plan. A 6.58% guaranteed return is good; it is not worth being one broken transmission from missing a payment.

If you are still shopping the loan rather than paying it down, the mortgage calculator handles the monthly side, and refinancing attacks the same interest from the other direction — by lowering the rate instead of the balance. If the credit card came up above, the minimum payment trap shows what that balance does when left alone.

Frequently asked questions

Last reviewed July 2026. Figures assume a US fixed-rate mortgage with interest charged monthly on the remaining balance and extra payments applied to principal, which is how standard American mortgages work. They cover principal and interest only, and exclude property tax, homeowners insurance, and mortgage insurance — note that prepaying can still end a PMI premium early, as described above, which short of a recast is the one way it lowers a monthly bill. The $264,162 balance is the 2026 US average reported by Experian and the 6.58% rate is the Freddie Mac 30-year average for the week of July 23, 2026 — both are examples for the math, not offers. Savings comparisons use a 22% marginal tax rate. Confirm your own note for prepayment terms and how your servicer applies extra payments.