Extra Payment Mortgage Calculator

Add an extra amount to every payment and watch the amortization schedule shrink — open the schedule to see the new payoff date.

How the Extra Payment Mortgage Calculator works

The calculator adds your chosen extra amount to each scheduled payment, applies 100% of that extra to principal, then re-runs the amortization month by month to find the new payoff date and total interest. Your required payment never changes; the extra simply shrinks the balance faster, so less interest accrues every following month. Unlike a fixed biweekly schedule, you set the extra to any value - $50, $317, or a $15,000 windfall.

The base monthly payment (P&I) uses the standard amortization formula:

M = P × [ r(1+r)ⁿ ] / [ (1+r)ⁿ − 1 ]

• M = required principal-and-interest payment
• P = current loan balance (principal)
• r = monthly rate = annual rate ÷ 12
• n = number of payments remaining

Each month the tool runs this loop:

1. Interest for the month = remaining balance × r.
2. Principal from the required payment = M − interest.
3. Add your extra amount (recurring and/or a one-time lump) entirely to principal.
4. New balance = old balance − (regular principal + extra).
5. Repeat until the balance hits $0, counting the months.

Because the extra is pure principal, every dollar removes all the future interest that dollar would have generated for the rest of the term - that is why small amounts compound into large savings.

The engine handles the cases that trip up a manual table: an extra large enough to clear the loan in the final month (it caps the payment at the remaining balance instead of overpaying); a one-time lump applied at a chosen month versus a steady monthly add; and any mix of the two. It assumes a fixed rate, so for an adjustable loan you re-run it after each reset with the new rate and current balance. Two outcomes it does not change on its own: your required payment (only a refinance or recast lowers that) and any prepayment penalty your note may carry - check both before you start.

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Example calculation

Below are three real scenarios showing how different extra amounts and balances change the outcome - every figure is recomputed from the full amortization schedule.

Example 1 - small recurring extra, big loan. A $300,000 loan at 6.5% for 30 years has a required payment of $1,896.20 and would cost $382,633 in interest over the full term. Add just $200/month (total payment $2,096.20): the loan is paid off in about 277 months (23.1 years) and total interest drops to $279,185. That is $103,449 saved and roughly 6 years 11 months cut off the term - from about $55,400 of extra principal spread over the loan.

Example 2 - aggressive recurring extra. A $250,000 loan at 7.0% for 30 years has a $1,663.26 payment and $348,772 in lifetime interest. Add $500/month: payoff falls to about 193 months (16.1 years) and interest to $167,033 - a $181,739 saving and almost exactly 14 years faster.

Example 3 - a one-time lump sum. Take the same $300,000 loan at 6.5%. Instead of monthly extras, apply a single $10,000 lump in month one. Payoff moves to about 327 months and interest drops to $329,032 - a $53,601 saving and 33 months earlier from one payment. Note the recurring $200/month in Example 1 saves nearly double, because it keeps attacking principal every single month rather than once.

Scenario	Loan / Rate	Extra	New payoff	Interest saved	Time saved
1	$300,000 @ 6.5%	$200/mo	23.1 yrs	$103,449	~6 yr 11 mo
2	$250,000 @ 7.0%	$500/mo	16.1 yrs	$181,739	~14 yr
3	$300,000 @ 6.5%	$10,000 once	27.3 yrs	$53,601	~2 yr 9 mo

Higher rates and earlier extra payments produce the biggest savings, because interest is front-loaded - in month one of Example 1, $1,625 of the $1,896.20 payment is pure interest and only $271.20 touches principal, so an early extra $200 nearly doubles the principal you knock off that month.

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Tips for using the Extra Payment Mortgage Calculator

• <strong>Clear higher-interest debt first.</strong> If you carry credit-card balances at 20%+ or a car loan above your mortgage rate, prepaying a 6% mortgage is the wrong order - route extra cash through the <a href="/debt-payoff-calculator/">debt payoff calculator</a> before touching the mortgage.
• <strong>Write "apply to principal" on every extra payment.</strong> Many servicers default extra money to next month's bill or to escrow, which does nothing for interest. Send it as a separate principal-only payment and confirm the next statement shows the balance dropped by that exact amount.
• <strong>Front-load extras early in the loan.</strong> Interest is front-loaded, so an extra $200 in year 2 erases far more total interest than the same $200 in year 25 - the earlier the dollar lands, the more future interest it kills.
• <strong>Round the payment up to a clean number.</strong> On a $1,896.20 payment, paying $2,000 adds about $103.80/month of principal you will barely feel, yet it trims roughly 50 months and about $62,877 in interest off a $300,000 loan at 6.5%.
• <strong>Check for a prepayment penalty before you start.</strong> A minority of loans charge a fee - often around 2% of the balance - if you pay down too much in the first 1-3 years; read your note or call the servicer before a lump sum triggers it.
• <strong>Keep an emergency fund first.</strong> Money sent to principal is locked in the house until you sell, refinance, or recast - top up your <a href="/emergency-fund-calculator/">emergency fund</a> before accelerating, because you cannot withdraw a prepaid mortgage in a crisis.
• <strong>After a big lump, ask for a recast, not a refinance.</strong> If you drop $20,000 or more on principal, a recast re-amortizes the loan for a small flat fee, lowering your required payment without a new rate or closing costs.
• <strong>Compare the guaranteed return to investing.</strong> Prepaying earns a risk-free return equal to your mortgage rate; if your rate is well below a diversified portfolio's expected return, run the trade-off in the <a href="/investment-calculator/">investment calculator</a> before committing cash to the house.
• <strong>Mind the mortgage-interest deduction if you itemize.</strong> Faster payoff reduces deductible interest - usually still worth it, but factor it into your effective rate when comparing prepaying to investing.
• <strong>Automate the extra so it actually happens.</strong> Set a recurring principal-only transfer the day after payday; manual "whatever is left over" extras almost always shrink to zero by month-end.

Recurring extra vs a one-time lump sum

A steady monthly extra almost always saves more total interest than a single lump of the same dollars, because it attacks principal every month instead of once - but a lump delivers an instant equity jump. A lump sum shines when you receive a windfall (bonus, tax refund, inheritance). A recurring extra is better for building a permanent habit and squeezing out the most interest.

Using a $300,000 loan at 6.5% (required payment $1,896.20, baseline interest $382,633), here is how the two approaches compare:

Approach	What you pay	Payoff	Interest saved
One-time $10,000 lump (month 1)	$10,000 once	27.3 yrs	$53,601
Recurring $200/month	~$55,400 over the loan	23.1 yrs	$103,449

The recurring plan costs more in total extra dollars but saves nearly double the interest and finishes 4 years sooner. The smartest move is often both: drop a lump when a windfall lands, then keep a small monthly extra running. To weigh investing a windfall instead of prepaying, model its growth in the future value calculator before committing it to the house.

Where extra money should go first

Prepaying a mortgage is one of the last places extra cash should go - clear higher-interest debt and build a cushion before sending a dollar to a cheap home loan. Because prepaying only earns a return equal to your mortgage rate, anything that costs or earns more comes first.

A workable priority order:

1. Capture any 401(k) employer match. A 50-100% match is an instant return no mortgage payoff can beat.
2. Kill debt above your mortgage rate. A 22% credit card costs about $1,100 a year per $5,000 carried, versus roughly $325 a year for the same $5,000 in a 6.5% mortgage - fix the order with the debt payoff calculator.
3. Fund 3-6 months of expenses in liquid savings; prepaid principal cannot be withdrawn in an emergency.
4. Then choose between extra mortgage payments and taxable investing based on your rate.

Only after those are covered does an extra mortgage payment make sense - and even then, the right amount is simply the largest one you can sustain.

Common mistakes to avoid

The most common mistake is sending extra money without telling the servicer to apply it to principal. If you just pay more, many lenders treat it as a prepayment of the next bill, advance your due date, or stuff it into escrow - none of which reduces your principal or your interest.

• Not labeling the payment. Always mark it "principal only" and verify the next statement shows the balance dropped by that exact amount.
• Prepaying a cheap mortgage while carrying expensive debt. Paying down a 6.5% mortgage while a 22% credit card sits unpaid loses money every month.
• Draining the emergency fund to prepay. Prepaid principal is illiquid; you cannot get it back without selling, refinancing, or recasting.
• Ignoring a prepayment penalty. A minority of loans charge for early payoff in the first few years - on a $250,000 balance, a 2% penalty is about $5,000.
• Assuming extra payments lower your monthly bill. They do not - the required payment stays the same; only a recast or refinance lowers it.

How to calculate extra payments by hand or in Excel

You can reproduce this tool in any spreadsheet with two built-in functions and a simple month-by-month table. First find the required payment, then build an amortization schedule that subtracts an extra amount each row.

Required principal-and-interest payment (positive result):

=-PMT(rate/12, years*12, loan_amount)

For a $300,000 loan at 6.5% over 30 years: =-PMT(0.065/12, 360, 300000) returns $1,896.20.

Then build the schedule. With the starting balance in cell B2, the monthly rate in $E$1, the payment in $E$2, and your extra in $E$3:

• Interest: =B2*$E$1
• Principal (incl. extra): =$E$2-(B2*$E$1)+$E$3
• New balance: =B2-(($E$2-(B2*$E$1))+$E$3)

Drag the rows down until the balance reaches zero - the row count is your new term, and summing the interest column gives total interest. For a quick shortcut on a fixed extra, =NPER(rate/12, -(payment+extra), loan_amount) returns the number of payments; compare that to 360 to see the months saved. By hand the loop is identical: interest = balance × (rate ÷ 12); principal = (payment - interest) + extra; new balance = balance - principal; repeat. For the underlying mechanics, see how loan interest works.

Is prepaying worth it? Benchmarks and a simple rule

Prepaying your mortgage earns a guaranteed, risk-free return equal to your interest rate - so the benchmark is simple: compare your mortgage rate to what your money would safely earn elsewhere.

• At a 6.5% rate, every extra dollar of principal earns an effective 6.5% return, guaranteed and free of investment risk.
• If a high-yield savings account or short CD pays less than your rate, prepaying wins on a risk-adjusted basis - compare with the savings calculator.
• If a diversified long-term portfolio is expected to return more than your rate, investing may win - but it carries risk that a guaranteed payoff does not.

The rate makes the case: an extra $200/month saves about $50,412 on a $300,000 loan at 4%, but $145,906 on the same loan at 8% - so the higher your rate, the stronger the case to prepay rather than invest. As a rough gauge, adding 10% to a 30-year payment typically cuts roughly 4-6 years off the term. There is no universal "right" amount - the best extra is the largest one you can sustain after a match, high-rate debt, and an emergency fund are covered.

Recast vs refinance after a lump sum

If you make a large one-time principal payment and want a lower monthly bill, a recast is usually cheaper and simpler than a refinance. Both can lower your payment, but they work very differently.

	Recast (re-amortize)	Refinance
What changes	Payment recalculated on the lower balance; same rate, same end date	New loan, new rate, new term, new closing costs
Typical cost	Small flat fee (often $150-$500)	2%-5% of the loan in closing costs
Changes your rate?	No	Yes (could be higher or lower)
Credit check / appraisal	Usually none	Usually required

Worked example: on a $300,000 loan at 6.5%, the balance after 5 years is about $280,833. Pay a $50,000 lump (balance ~$230,833) and recast over the remaining 25 years and the required payment falls from $1,896.20 to about $1,558.60 - same rate, no closing costs. Refinance makes sense mainly when market rates are meaningfully lower than your current rate; run that separately in the mortgage refinance calculator. Note that prepaying without a recast keeps the high required payment, which finishes the loan even faster.

How this differs from biweekly payments

This calculator handles any custom extra amount, while the biweekly method is one specific schedule that forces exactly 13 monthly payments per year. Biweekly works by paying half your monthly amount every two weeks; because there are 52 weeks, you make 26 half-payments - the equivalent of 13 full payments - and that one extra payment per year quietly accelerates the loan.

The difference is control. Biweekly locks you into roughly an 8.3% annual boost (one extra payment spread over 12 months) and nothing else. A custom extra lets you pay $50, $200, or $1,000 - whatever your budget allows - add a one-time lump from a bonus, change the amount any month, or test several scenarios side by side. If you specifically want the fixed 13-payments-a-year structure, use the biweekly mortgage calculator. If you want flexibility, a lump sum, or to compare amounts, this tool is the right one. For your base payment and full amortization, start with the mortgage calculator.

Advanced uses: PMI removal, windfall timing, and ARMs

Beyond a simple monthly add, custom extra payments let you plan PMI removal, windfall timing, and adjustable-rate resets.

• Reaching 20% equity to drop PMI. If you put down less than 20%, extra principal pushes your loan-to-value to 80% sooner, letting you request private mortgage insurance removal - a real monthly saving on top of the interest cut.
• Windfall scheduling. Model a recurring annual lump, such as a $5,000 tax refund: on a $300,000 loan at 6.5%, $5,000 every 12 months saves about $158,003 in interest and ends the loan in 228 months (19 years) instead of 360.
• Tax angle. If you itemize and deduct mortgage interest, faster payoff reduces that deduction; for most borrowers the guaranteed interest savings still outweigh it, but include it when comparing prepaying to investing.
• Adjustable-rate loans. This engine assumes a fixed rate. After each reset, re-enter the new rate and current balance for an accurate projection.

Before starting any plan, confirm there is no prepayment penalty and that your servicer applies extras to principal on the date received, not the next due date.

Extra monthly principal cheat sheet: $300,000 at 6.5%

Even a small custom extra payment shortens your term and slashes interest, and unlike the biweekly method you can choose any amount. The table below uses a $300,000 loan at 6.5% over 30 years, where the standard payment is $1,896.20 and total interest with no extra is about $382,633. Every figure assumes the extra goes straight to principal starting in month one; numbers are recomputed from a full amortization. Run your own loan above, then send each extra as a principal-only payment.

Extra per month	New payoff time	Years saved	Total interest	Interest saved
$0 (baseline)	30 yr 0 mo	-	$382,633	$0
$50	27 yr 10 mo	2.2	$349,052	$33,582
$100	26 yr 0 mo	4.0	$321,639	$60,995
$200	23 yr 1 mo	6.9	$279,185	$103,449
$300	20 yr 10 mo	9.2	$247,518	$135,115
$500	17 yr 6 mo	12.5	$202,874	$179,759

The pattern is clear: each step up in extra principal saves disproportionately more interest, because the dollars land while the balance - and therefore the monthly interest - is still high.

Related on this site

Mortgage Calculator · Biweekly Mortgage Calculator · Mortgage Refinance Calculator · Debt Payoff Calculator · Down Payment Calculator · 15-Year vs 30-Year Mortgage

For a related deep dive, see CFPB on paying down your mortgage faster.

Extra Payment Mortgage Calculator — frequently asked questions

Where should extra money go?

Pay off higher-interest debt first; mortgage prepayment makes sense when no costlier debt remains.

Is there a penalty?

Most modern mortgages have no prepayment penalty, but confirm with your lender.

Is prepaying a mortgage worth it?

It guarantees a return equal to your mortgage rate, but only after costlier debt is gone.

Lump sum or monthly extra?

Both help; monthly extra is easier to sustain and compounds savings steadily.

How much interest does an extra $100 a month save on a $300,000 mortgage at 6.5%?

About $60,995 in interest, and it pays the loan off roughly 4 years early. On a $300,000 loan at 6.5% over 30 years, the payment is $1,896.20 and total interest is about $382,633. Adding $100 to principal each month cuts total interest to about $321,639 and ends the loan in 312 months (26 years) instead of 360. Try your own numbers in the <a href="/extra-payment-mortgage-calculator/">extra payment mortgage calculator</a>.

What happens if I pay an extra $200 a month on a $400,000 loan at 7%?

You save about $126,617 in interest and finish about 5.8 years early. A $400,000 loan at 7% over 30 years has a $2,661.21 payment and roughly $558,036 in total interest. Sending an extra $200 toward principal every month drops total interest to about $431,418 and pays the loan off in 291 months instead of 360. The earlier you start, the bigger the savings.

Is it better to make one $12,000 lump-sum payment or pay $100 extra each month?

For total interest a single $12,000 lump early wins slightly, but the monthly habit pays the loan off sooner. On a $300,000 loan at 6.5%, a $12,000 lump in year one saves about $63,048 and ends the loan in 321 months. Spreading the same $12,000 as $100/month saves about $60,995 but finishes earlier, at 312 months. Lump sums save a touch more interest; recurring extras shorten the term faster.

How much does a one-time $20,000 lump sum save on a $300,000 mortgage at 6.5%?

About $97,429 in interest, and it shortens the loan by roughly 5 years. On the $300,000 loan at 6.5% (360 months, ~$382,633 total interest), applying a $20,000 lump to principal in year one cuts total interest to about $285,204 and pays the loan off in 299 months. A lump works because it removes high-balance interest you would otherwise pay for decades. Confirm the payment is applied to principal.

Should I pay off a 22% credit card or prepay my 6.5% mortgage first?

Pay off the credit card first - it costs far more. Carrying $5,000 on a 22% card costs about $1,100 in interest in the first year alone, while the same $5,000 in a 6.5% mortgage costs only about $325 a year. Every dollar against the card earns a guaranteed 22% return versus 6.5%. Clear high-interest debt with our <a href="/debt-payoff-calculator/">debt payoff calculator</a> before prepaying a cheap mortgage.

How is the extra payment calculator different from the biweekly mortgage calculator?

This one handles any custom extra amount; the biweekly tool models one fixed method. The <a href="/biweekly-mortgage-calculator/">biweekly mortgage calculator</a> assumes you pay half your payment every two weeks, which equals 13 full payments a year - a set schedule. The extra payment calculator lets you add any amount monthly, yearly, or as a lump sum, so you can model $50, $317, or a $15,000 windfall.

What is the difference between a mortgage recast and a refinance after a lump sum?

A recast re-amortizes your current loan after a lump sum to lower the payment; a refinance replaces the loan entirely. After paying $50,000 toward a $300,000 loan at 6.5% (balance ~$280,833 after 5 years, ~$230,833 after the lump), recasting over the remaining 25 years drops the payment from $1,896.20 to about $1,558.60. A recast keeps your rate and costs a small fee (often $150-$500); a refinance changes the rate and has full closing costs.

Does prepaying my mortgage lower my monthly payment?

No - extra principal shortens the term but keeps the same monthly payment, unless you recast. When you send extra to principal, the loan ends sooner and you pay less total interest, but your required payment stays fixed. To actually lower the monthly amount after a big lump sum, ask your servicer to recast (re-amortize) the loan. On a $300,000 loan at 6.5%, a $50,000 lump plus a recast can cut the $1,896.20 payment to about $1,558.60.

How much does paying an extra $300 a month save on a $350,000 loan at 6.75%?

About $151,699 in interest, and it ends the loan roughly 8.4 years early. A $350,000 loan at 6.75% over 30 years has a $2,270.09 payment and about $467,234 in total interest. Adding $300 to principal each month cuts total interest to about $315,535 and pays off the loan in 259 months instead of 360. Higher rates make extra principal even more powerful.

Is rounding my mortgage payment up to the next $100 worth it?

Yes - on a $300,000 loan at 6.5%, rounding up saves tens of thousands. The payment is $1,896.20; rounding to $2,000 adds about $103.80 to principal each month. That cuts total interest from about $382,633 to roughly $319,757 (about $62,877 saved) and ends the loan in 310 months instead of 360. It is a painless way to prepay because the extra is small and automatic each month.

Should I check for a prepayment penalty before paying extra?

Yes - always confirm there is no prepayment penalty before making large extra payments. Most modern conforming loans have none, but some charge a penalty in the first 1-3 years, often around 2% of the balance. On a $250,000 balance that 2% is about $5,000, which could wipe out your interest savings. Read your note or call your servicer; small recurring extras rarely trigger penalties, but big lump sums can.

How much does an extra $5,000 once a year do on a $300,000 mortgage at 6.5%?

An annual $5,000 toward principal saves about $158,003 in interest and ends the loan 11 years early. On the $300,000 loan at 6.5% (normally 360 months, ~$382,633 interest), adding $5,000 every 12 months cuts total interest to about $224,631 and pays the loan off in 228 months. Yearly lumps from a bonus or tax refund are an easy, low-effort way to make a large dent.

Is prepaying a 4% mortgage worth it, or should I invest instead?

Prepaying a 4% mortgage gives a guaranteed 4% return, which is often less than long-term investing. On a $300,000 loan at 4%, an extra $200/month still saves about $50,412 in interest and ends the loan about 6 years early. But at 4%, that guaranteed payoff competes with a diversified portfolio's higher expected return. At 8%, the same extra $200 saves about $145,906 - so the higher your rate, the stronger the case to prepay.

How much sooner will an extra $1,000 a month pay off a $500,000 loan at 7.25%?

It pays the loan off about 14 years early and saves roughly $382,324 in interest. A $500,000 loan at 7.25% over 30 years has a $3,410.88 payment and about $727,917 in total interest. Adding $1,000 to principal monthly cuts total interest to about $345,593 and ends the loan in 192 months (16 years) instead of 360. Large extras on big, high-rate loans produce the most dramatic savings.

Where should my extra money go first - the mortgage, an emergency fund, or my 401(k)?

Generally: emergency fund and high-interest debt first, then employer-matched 401(k), then prepay the mortgage. Build a cushion with the <a href="/emergency-fund-calculator/">emergency fund calculator</a> and capture any free 401(k) match before prepaying, since a match is an instant 50-100% return that beats a 6.5% mortgage payoff. Prepaying a low-rate mortgage is usually one of the last priorities, after a 22% credit card and free retirement money.

Guides & articles

• How Much Does Paying Extra on Your Mortgage Save?
• Should You Pay Extra on Your Mortgage, or Use That Money Elsewhere?

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