Extra Payment Calculator

What is an extra mortgage payment?

An extra mortgage payment is any amount you send beyond the scheduled principal-and-interest installment, designated to reduce principal. It is the simplest acceleration tool available: no refinance, no closing cost, no requalification, no new note. You simply pay $2,528.27 as scheduled and add a fixed amount on top — $100, $200, $300 — and that added money shortens the amortization schedule by exactly as much as it reduces the balance.

The mechanism is arithmetic rather than persuasion. Interest each month is the balance times the monthly rate, 6.50% ÷ 12 = 0.005416667. On a $400,000 loan that is $2,166.67 of interest in payment 1, leaving $361.61 of principal. Add $200 and the payment becomes $2,728.27 while interest stays at $2,166.67, so $561.61 goes to principal and the balance drops to $399,438.40. Next month's interest is computed on that lower figure. The reduction compounds: every dollar of principal you remove today stops earning 6.50% for every remaining month of the loan.

The size of the return surprises most people. On the benchmark loan, $200 a month costs $58,600 of extra cash across 293 payments and returns $111,892 of avoided interest — $1.91 for every $1 committed. Even $100 a month costs $32,200 and returns $63,917, a ratio of $1.99 because the smaller extra persists longer. Returns are not proportional to the amount, though: $400 a month returns $180,154 against $100's $63,917 — 2.8 times the saving for 4 times the money. The lesson runs through this whole page: consistency and timing beat magnitude. Alternative delivery methods — a biweekly schedule, an annual lump sum, round-up — are compared in the tables below and detailed in the extra payments guide.

How to use this calculator

1. Enter your loan balance, interest rate, and scheduled monthly principal-and-interest payment from your statement.
2. Enter the extra amount you can sustain every month, not the maximum you could pay once.
3. Optionally add a one-time lump sum and set the month it applies, so you can compare a bonus against a recurring habit.
4. Click Calculate to see the new payoff date, months saved, total interest saved, and total extra paid.
5. Run at least three amounts — $100, $200, $300 — and read the interest saved column next to the total extra paid column before choosing.

A realistic input set for the benchmark loan: balance $400,000, rate 6.50%, 360 months, scheduled payment $2,528.27, extra $200 a month. Add a second scenario with the same $200 applied as a single $2,400 lump every January to see what timing alone is worth — on this loan it is $4,218 of interest. For a full picture, include escrow in your budget even though it is not part of the calculation: property tax at roughly $416.67 a month and insurance at $125 a month on a $500,000 home bring the payment that actually leaves your account to $3,069.94, and the extra must fit on top of that figure, not inside it.

How it is calculated

The calculator runs a month-by-month amortization loop with a modified payment. Each month it charges interest on the current balance, adds your extra to the scheduled payment, subtracts the total from the balance, and repeats until the balance reaches zero:

New balance = (Old balance + Old balance × i) − (Scheduled payment + Extra)

Here i is the monthly rate, annual rate ÷ 12. The loan ends when the balance first falls to zero, and that month is your new payoff month. Total interest is the sum of every monthly interest charge; interest saved is the difference between that sum and the scheduled total of $510,178.

Worked example: $200 extra every month on $400,000 at 6.50%

Step 1: monthly rate is 6.50% ÷ 12 = 0.005416667. Step 2: scheduled payment is $2,528.27; with the extra it is $2,728.27. Step 3: payment 1 charges $400,000 × 0.005416667 = $2,166.67 of interest, so principal is $2,728.27 − $2,166.67 = $561.61 instead of $361.61, and the balance becomes $400,000 + $2,166.67 − $2,728.27 = $399,438.40. Step 4: over year 1 you send $32,739.24 to the lender, of which $25,796 is interest and $6,944 reduces principal — against $25,868 of interest and $4,471 of principal on the scheduled plan.

Step 5: keep looping and the schedule closes at payment 293 instead of payment 360, which is 67 months — 5 years 7 months — early. Step 6: total interest is $398,286 instead of $510,178, so you save $111,892. Step 7: measure what it cost. The extra runs for 293 payments, so $200 × 293 = $58,600 of additional principal. $111,892 ÷ $58,600 = 1.91, meaning every extra dollar returns $1.91 of avoided interest. Step 8: check the other end of the range. At $100 a month the loan runs 322 payments, total extra is $32,200, interest saved is $63,917, and the ratio is $1.99 — the smaller habit earns more per dollar committed.

Worked scenarios

All three tables hold the loan at $400,000 unless stated, use the 6.50% benchmark rate and 360-month term, and exclude taxes, insurance, and PMI.

Extra monthly amounts: $100, $200, $300, $500

Two readings matter. First, $500 a month retires the loan 10 years 7 months early and returns $205,557 — larger than the entire down payment most buyers bring. Second, the return per dollar falls from $1.99 at $100 to $1.76 at $500, because a bigger extra ends the loan sooner and therefore earns its saving over fewer months. Choose the amount you will still be paying in year eight.

Rate sensitivity: the same $200 extra at three rates

The same $200 habit returns $85,713 at 5.50% and $142,513 at 7.50% — a 66% wider return for an unchanged effort, because each dollar of principal removed defends a higher rate. This is also why the acceleration case gets stronger as rates rise, and why it is weaker on a loan you may refinance anyway. Schedule assumptions and current pricing live on the rates page.

Same annual budget: four delivery methods

With roughly the same annual dollars committed, spreading wins over an annual lump by $4,218 because principal falls in every month instead of once. The biweekly schedule leads by $5,604 over the flat $200, since its 13th payment arrives in installments throughout the year. Pick the method your cash flow will actually sustain — a perfect plan that stops in month nine earns nothing.

Key details of how extra payments behave

• Principal-only instruction is mandatory: unmarked extra dollars can be posted to prepaid interest or your next installment. Write "apply to principal" once, then confirm the allocation on the following statement and the annual year-end summary.
• The return equals your interest rate: 6.50% guaranteed, compounded monthly, with no market risk and no tax on the saving. A competing investment must clear 6.50% after tax to win.
• Returns are sub-linear: $100 returns $63,917, $200 returns $111,892, $400 returns $180,154. Four times the money does not buy four times the saving, because the loan ends sooner.
• Year one is where the shift shows: with $200 extra, principal repaid rises from $4,471 to $6,944 in the first twelve months while interest barely moves, from $25,868 down to $25,796.
• Biweekly equivalence: a biweekly plan is $2,528.27 of extra per year, or $210.69 a month. Any extra near that figure reproduces the biweekly result — see the biweekly calculator.
• Recasting trades payoff for cash flow: after a $50,000 lump the balance is $345,529.10; re-amortized over the 348 remaining months the payment falls from $2,528.27 to about $2,184, roughly $344 less, typically for a $250 to $500 fee.
• Prepayment penalties are prohibited on qualified mortgages and absent from most conventional, FHA, and VA loans. Portfolio and non-QM notes occasionally cap curtailments at 1% to 2% — read the note before large one-time sends.
• Sequencing beats enthusiasm: a credit card at 22% outranks a 6.50% mortgage every time, and an employer 401(k) match is an immediate 50% to 100% return. Fund the match, clear high-rate debt, then attack principal.

Tips for 2026

1. Automate the extra on payday. Schedule the transfer for the day after your paycheck lands, at an amount you have never once failed to cover. A $200 instruction that survives 293 months returns $111,892; a $500 instruction that stops in month six returns nothing.
2. Start at $100 and step up annually. $100 a month already removes 38 months and $63,917. Raise it by $50 or $100 whenever income rises rather than committing to the maximum today.
3. Send windfalls immediately. A tax refund or bonus applied in month 12 on this loan contributes to 281 remaining payments of saving; the same money arriving in month 240 has 120 left. Timing is worth thousands on identical dollars.
4. Verify allocation every statement cycle. Look at the principal column, not the payment confirmation. The amortization guide shows what the split should look like at your balance.
5. Clear higher-rate debt first. Order every balance by APR, pay the 20% cards down, then redirect that entire payment to principal. The habit and the amount both transfer — only the destination changes.
6. Hold three to six months of payments in reserve. On this example that is $9,210 to $18,420 including taxes and insurance. Draining savings to prepay turns a 6.50% problem into a 22% one the first time you reach for a card.
7. Do not stop tracking after year one. Your year-end statement prints total interest and total principal paid. Compare those two numbers against your projection annually; a misapplied recurring extra reveals itself within twelve months.

Common mistakes with extra payments

• Never designating the payment as principal. The most common failure. A $200 monthly add-on posted as an advance on next month's due date changes nothing: same balance, same interest, same payoff month. Send written instructions and verify.
• Expecting linear returns. $400 does not save twice what $200 saves — it returns $180,154 against $111,892, and the per-dollar ratio falls from $1.91 to $1.80. Bigger is better, just less than proportionally so.
• Prepaying a 6.50% loan while carrying 22% cards. Every dollar to the card saves 22%; to the mortgage, 6.50%. Sequence matters more than volume, and the ordering never changes.
• Emptying the emergency fund to accelerate. Three to six months of payments — $9,210 to $18,420 here — must stay liquid. One financing gap at card rates erases years of careful prepayment.
• Stopping and restarting. The saving is back-loaded. Interruptions cost more than modest amounts do, so a smaller permanent extra beats an aggressive plan with gaps in it.
• Ignoring the recast option. If your goal is a lower payment rather than an earlier payoff — retirement, a career change, reduced hours — a $250 to $500 recast after a lump cuts this example by about $344 a month. Extra payments alone never lower the obligation.

Frequently asked questions

How much extra do I need to pay off five years early? On a $400,000 loan at 6.50%, about $175 a month. That closes the loan at payment 300 instead of 360, costs $52,500 of extra principal across 25 years, and returns $101,026 of avoided interest — total interest of $409,152 instead of $510,178.

Is it better to make extra payments monthly or as a lump sum? Monthly. $200 spread across every month saves $111,892 while the identical $2,400 annual lump saves $107,674 — a $4,218 difference, because principal falls in all twelve months instead of once. Lump sums still win when the alternative is not sending anything at all.

Will extra payments lower my monthly payment? Not by default. The payment stays $2,528.27 and the loan simply ends sooner — a $500 extra finishes at payment 233 with the payment unchanged. Only a recast at a $250 to $500 fee, or a refinance, converts principal progress into a smaller obligation.

How much interest will I save with $200 a month extra? $111,892 on the benchmark loan. The schedule ends at payment 293 instead of 360 — 5 years 7 months early — and total interest falls from $510,178 to $398,286. The extra itself totals $58,600, so each dollar returns $1.91.

Should I pay extra on the mortgage or invest? Answer in order: keep three to six months of payments liquid, capture the full employer 401(k) match, eliminate anything charging more than 6.50%, then compare. Prepayment earns a guaranteed 6.50%; equity averages higher over decades but can be negative in any single year.

Do I need lender approval to make extra payments? Not on qualified mortgages, which cannot carry prepayment penalties, nor on most conventional, FHA, or VA loans. Check your note for portfolio or non-QM language, then send written instructions that the amount applies to principal rather than to your next due date.

Does this work on an interest-only or adjustable-rate loan? On interest-only, the entire extra reduces principal immediately since scheduled principal is zero, which makes it unusually effective. On an ARM the mechanics hold through the fixed period; after a reset the payment and rate change, so re-run the calculation at each adjustment.

How does a biweekly schedule compare to a fixed extra? A biweekly plan is worth $2,528.27 a year, or $210.69 a month of extra principal. On this loan it returns $117,496 and finishes in 24 years 2 months, against $111,892 and 24 years 5 months for a flat $200 monthly — essentially the same tool with a different calendar.

Related calculators

• Biweekly Calculator — the 26-payment schedule compared
• Mortgage Payoff Calculator — lump-sum timing and payoff dates
• Mortgage Calculator — baseline payment and full amortization
• Refinance Calculator — shorter term versus prepayment
• 30-Year Mortgage Calculator — the benchmark loan schedule
• Mortgage FAQ — answers to the questions buyers ask most