Extra Mortgage Payment Calculator (Extra Principal)
See how recurring monthly extra payments, one extra payment per year, or a one-time lump sum can shorten your mortgage payoff timeline and reduce total interest. Educational use only. Not financial advice.
Inputs
Results
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 |
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: Extra-payment payoff behavior, monthly-versus-lump-sum assumptions, and workflow routing.
See our editorial policy and methodology.
Report corrections: admin@practicalfinancetools.com
Use this calculator when you need the broad extra-payment payoff plan before narrowing to principal-only or lump-sum-only moves
Start here when the question is still broad: extra mortgage payment calculator scenarios, recurring extra payments, or how to calculate mortgage payoff changes with additional principal payments under one consistent baseline. If the only thing you need is a pure principal-only or lump-sum workflow, then move next to the additional principal calculator.
Choose the right calculator
Use this page for broad mortgage extra-payment planning: recurring monthly extras, one extra payment per year, and general payoff acceleration. If your main question is how a lump sum or principal-only payment should be modeled, use the dedicated additional principal calculator.
Worked example
Example inputs: $300,000.00 principal, 6.5% note rate, 30-year term, $300.00 extra monthly.
| Scenario | Payoff time | Total interest (estimate) |
|---|---|---|
| Baseline (no extra) | 360 months (30y 0m) | $382,633.47 |
| With extra monthly | 250 months (20y 10m) | $247,518.30 |
| Savings | 110 months (9y 2m) | $135,115.17 |
Extra principal payment calculator inputs to verify
- Principal amount excludes escrow items and fees.
- Rate is the note rate (not APR).
- Extra payments are applied as principal-only by your servicer.
- If you plan a lump sum, model the timing as early as possible.
Match your statement
- Confirm extra payments post as principal-only, not "paid ahead."
- Check the payment posting date; timing can shift interest slightly.
- If a lump sum posts after the payment due date, model a later month.
Assumptions & limitations
- Estimates assume extra payments are applied as principal-only (not "paid ahead").
- Escrow items (taxes/insurance/HOA) are separate from principal and interest payoff math.
- Timing and lender rounding/posting rules can change real statements; use results for comparisons.
Common pitfalls
- Extra payments typically reduce payoff time, not the required monthly payment (unless you recast).
- Some lenders have rules for how extra payments are applied; confirm "principal-only" application.
- If your loan has a prepayment penalty, the savings may be reduced.
- Escrow items (tax/insurance) are separate from principal and interest; extra payments don't reduce escrow.
If results look off
- Confirm your interest rate is the note rate, not APR.
- Double-check the remaining term in months.
- Make sure extra payments are applied to principal-only in your scenario.
- If you are modeling a lump sum, test an earlier timing to see the sensitivity.
Monthly extra vs lump sum timing
A lump sum early can save more interest than the same total spread out. If your lump sum arrives later, compare it to a smaller monthly extra that starts now and see which payoff date is earlier.
| Scenario | When extra is applied | Why it matters |
|---|---|---|
| Monthly extra | Starts now | Reduces balance earlier, lowering interest sooner. |
| Lump sum (early) | Month 3-6 | Often beats the same total spread out later. |
| Lump sum (late) | Month 18+ | Can save less; compare against smaller monthly extras. |
Scenario checklist
- Keep the baseline constant before comparing options.
- Test at least two extra amounts to see sensitivity.
- Review total interest saved and payoff date together.
Related guide
Related topics
Related tools
References
- CFPB: Mortgage resources
- CFPB: What is an amortization schedule?
Last updated: 2026-04-04
How we calculate
- Baseline schedule uses standard amortization for principal & interest.
- Extra payments are applied to principal (reducing future interest).
- Results assume the lender applies extra payments to principal and that there is no prepayment penalty.
FAQ
If I pay $300 extra on my mortgage, what happens?
Mortgage extra principal calculator: what inputs do I need?
One extra mortgage payment per year: how do I model that?
Mortgage calculator with extra payments and lump sum: does this support lump sums?
Does an extra payment reduce my required monthly payment?
Monthly vs one-time extra: which is better?
What about prepayment penalties?
Should I invest instead?
Is rounding handled exactly like my lender?
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: 2026-04-04