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Extra Principal Payment Calculator (Mortgage)

Use this additional principal payment calculator to estimate how a lump-sum or principal-only payment changes payoff time and total interest. Compare a one-time principal payment to recurring monthly extras under the same baseline. Educational use only. Not financial advice.

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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)
MonthPaymentExtraInterestBalance
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

Reviewed By

Written by: Practical Finance Tools Site Owner (Site owner and product editor).

Reviewed by: Practical Finance Tools Methodology Review (Formula and assumptions review) on .

Secondary review: Practical Finance Tools Editorial Review (Editorial standards review).

Review scope: Principal-only and lump-sum payoff assumptions, result boundaries, and next-step comparison guidance.

See our editorial policy and methodology.

Report corrections: admin@practicalfinancetools.com

Use this calculator for additional principal and lump-sum scenarios

  • Model a bonus, refund, or windfall as a one-time principal payment.
  • Compare principal-only posting to a recurring monthly extra.
  • Stress-test "paid ahead" vs principal-only assumptions with the same loan baseline.
  • If you mainly want recurring monthly extra-payment planning, use the Extra Payment Calculator.

Additional principal 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% note rate, 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.

Related tools

Biweekly mortgage payments Recurring monthly extra payments Mortgage payment Amortization schedule

References

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How we calculate

  • Baseline schedule uses standard amortization for principal and interest.
  • A one-time or recurring additional principal payment reduces the balance, which reduces future interest.
  • This page is designed for principal-only and lump-sum scenarios, assuming extra amounts are applied correctly and there is no prepayment penalty.

FAQ

How do I model a lump-sum principal payment?
Enter the same loan baseline, then compare a one-time principal payment to a recurring monthly extra. This is the better page when your main question is a bonus, refund, or other lump sum.
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: 2026-04-03