Extra Principal Payment Calculator (Mortgage)
Use this extra principal payment calculator to estimate how additional principal payments change payoff time and total interest. Compare a monthly extra vs a one-time principal payment under consistent assumptions. Educational use only. Not financial advice.
Inputs
Base P&I: $2,275.44
Month 1 = first payment
0 = no end date
Month 1 = first payment
Results
Interest saved (est.)
$87,527.21
Extra paid (total)
$0.00
Additional principal paid
Time saved
4 yr 10 mo
New payoff time
25 yr 2 mo
New monthly P&I
$2,425.44
Required P&I stays the same; extra is added when active
Total interest (base)
$459,160.16
Total interest (new)
$371,632.95
Schedule (first 24 months)
| Month | Payment | Extra | Interest | Balance |
|---|---|---|---|---|
| 1 | $2,275.44 | $150.00 | $1,950.00 | $359,524.56 |
| 2 | $2,275.44 | $150.00 | $1,947.42 | $359,046.53 |
| 3 | $2,275.44 | $150.00 | $1,944.84 | $358,565.93 |
| 4 | $2,275.44 | $150.00 | $1,942.23 | $358,082.71 |
| 5 | $2,275.44 | $150.00 | $1,939.61 | $357,596.88 |
| 6 | $2,275.44 | $150.00 | $1,936.98 | $357,108.42 |
| 7 | $2,275.44 | $150.00 | $1,934.34 | $356,617.31 |
| 8 | $2,275.44 | $150.00 | $1,931.68 | $356,123.55 |
| 9 | $2,275.44 | $150.00 | $1,929.00 | $355,627.10 |
| 10 | $2,275.44 | $150.00 | $1,926.31 | $355,127.97 |
| 11 | $2,275.44 | $150.00 | $1,923.61 | $354,626.14 |
| 12 | $2,275.44 | $150.00 | $1,920.89 | $354,121.58 |
| 13 | $2,275.44 | $150.00 | $1,918.16 | $353,614.30 |
| 14 | $2,275.44 | $150.00 | $1,915.41 | $353,104.26 |
| 15 | $2,275.44 | $150.00 | $1,912.65 | $352,591.47 |
| 16 | $2,275.44 | $150.00 | $1,909.87 | $352,075.89 |
| 17 | $2,275.44 | $150.00 | $1,907.08 | $351,557.52 |
| 18 | $2,275.44 | $150.00 | $1,904.27 | $351,036.35 |
| 19 | $2,275.44 | $150.00 | $1,901.45 | $350,512.35 |
| 20 | $2,275.44 | $150.00 | $1,898.61 | $349,985.52 |
| 21 | $2,275.44 | $150.00 | $1,895.75 | $349,455.83 |
| 22 | $2,275.44 | $150.00 | $1,892.89 | $348,923.27 |
| 23 | $2,275.44 | $150.00 | $1,890.00 | $348,387.82 |
| 24 | $2,275.44 | $150.00 | $1,887.10 | $347,849.48 |
Example
Try $360,000 at 6.50% for 30 years, then compare: (1) $100-$300 extra per month, and (2) a one-time principal payment (e.g., from a bonus) early in the loan. Keep the baseline constant when you compare scenarios.
Example output (monthly extra)
Example inputs: $$360,000.00 loan, 6.5% APR, 30-year term, $$200.00 extra monthly.
| Scenario | Payoff time | Total interest (estimate) |
|---|---|---|
| Baseline | 360 months | $459,160.16 |
| With extra | 287 months | $350,243.31 |
| Savings | 73 months | $108,916.85 |
When extra principal can make sense
- You have a stable emergency fund and want guaranteed interest savings.
- Your mortgage rate is meaningfully higher than your expected after-tax return.
- You value payment certainty over investment volatility.
- You plan to keep the home long enough for savings to compound.
Related guides
Mortgage payoff topic hub Extra mortgage payments Principal-only checklist Amortization with extra payments One extra payment per year Recast vs extra payments
Extra principal payment calculator checklist (principal-only)
- Confirm the payment is applied to principal, not future due dates ("paid ahead").
- Check for prepayment penalties and whether your loan allows principal-only payments.
- Keep your regular payment unchanged when comparing scenarios.
- If you want a lower required payment, look into a recast (if available) instead of expecting extra payments to reduce the bill.
Common pitfalls
- Escrow (taxes/insurance) typically does not change when you pay extra principal.
- Servicer posting rules can affect results; verify how extra payments are applied.
- Paying extra principal can reduce liquidity; keep an emergency fund in mind.
Match your statement
- Confirm the extra amount shows as a principal-only transaction on your statement.
- Check whether the servicer applies extra payments immediately or after the regular payment posts.
- If you see "paid ahead," ask how to apply future extras as principal-only.
If results look off
- Confirm the interest rate is the note rate (not APR).
- Double-check the remaining term and starting balance.
- Make sure the extra payment is applied to principal-only in your scenario.
If you might sell or refinance
If you expect to move within a few years, compare the interest saved over that window instead of the full term. The calculator can still help by showing how quickly the balance falls with different extra amounts.
How to choose an extra amount
- Start with an amount you can keep for 12+ months.
- Check that it does not reduce your emergency fund below target.
- Revisit after rate changes, escrow adjustments, or income shifts.
Example comparisons
- Compare $200 monthly extra vs a $5,000 lump sum in month 6.
- Test a higher rate to see the impact on interest savings.
- Keep the baseline constant so you can see the true difference.
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How we calculate
- Baseline schedule uses standard amortization for principal and interest.
- Additional principal reduces the balance, which reduces future interest.
- This assumes extra amounts are applied as principal-only and that there is no prepayment penalty.
FAQ
Extra principal payment calculator: what does it do?
It estimates how paying extra principal (monthly or one-time) can shorten payoff time and reduce total interest compared to a baseline schedule.
Does additional principal lower my required monthly payment?
Usually no. Extra principal tends to shorten the term. Your required payment typically changes only if you recast the loan.
Monthly extra vs lump sum: which saves more?
Earlier principal reduction often saves more interest. A smaller monthly extra can beat a larger lump sum that happens later.
What is "paid ahead" and why does it matter?
Some servicers treat extra payments as covering future due dates instead of reducing principal as much as you expect. Confirm your extra is applied as principal-only.
Does this include taxes and insurance (escrow)?
No. This focuses on principal and interest. Escrow items are separate and typically do not change when you pay extra principal.
What is a mortgage recast?
A recast is when the servicer re-amortizes your remaining balance (often after a lump-sum principal payment) to reduce the required monthly payment while keeping the same interest rate and maturity date. Not all loans allow it and fees may apply.
Should I worry about prepayment penalties?
Some loans have prepayment penalties or restrictions. This calculator assumes no prepayment penalty. Check your note or ask your servicer before making extra principal payments.
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Disclaimer
Educational use only. Not financial advice. Results are estimates based on the inputs and assumptions shown on this page. Verify details with lenders, card issuers, and professionals.
Last updated: 2026-02-17