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Mortgage Lump Sum Calculator
See what a one-time principal payment could save—and whether keeping your payment or estimating a recast better matches your goal.
Primary estimateLive · USD
Estimated result
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Based on the assumptions entered.
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Scenario comparison
Longer bars represent the larger value.
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What this result means
A principal-only lump sum reduces the balance on which future interest accrues. Keeping the payment unchanged usually shortens payoff; estimating a recast spreads the lower balance over the remaining months and lowers the required payment.
How this calculator works
The selected lump sum is applied in the chosen payment month. The unchanged-payment strategy continues the original scheduled payment; the recast strategy recalculates payment from the lower balance and remaining months.
Worked example
For example, apply $30,000 to a $350,000 mortgage in the next payment month. Compare keeping the scheduled payment with estimating a recast, then add a recurring extra amount to see how the payoff and interest totals change together.
Assumptions and limitations
- Principal-only application in the selected month
- Fixed rate and monthly compounding
- Future monthly extras begin with the lump-sum month
- Servicer processing rules are not modeled
Frequently asked questions
Does a lump-sum mortgage payment reduce the monthly payment?
Usually not by itself. A principal-only lump sum reduces the balance and can shorten payoff, but the required payment generally stays the same unless the lender approves a recast or you refinance.
Is it better to pay a mortgage lump sum or make monthly extra payments?
Earlier principal reductions generally avoid more future interest, but the best timing depends on cash availability, emergency savings, lender rules, and other financial priorities. The calculator lets you model both together.
How should a lump-sum mortgage payment be applied?
Ask the servicer to apply it as a principal-only payment and confirm how it appears on the loan. Otherwise, a servicer may treat money differently under its payment rules.
Can I add monthly extra payments too?
Yes. Enter an optional recurring monthly amount beginning in the lump-sum month.
Can a mortgage have a prepayment penalty?
Some loans may charge a penalty for certain early payments. Finly does not model penalties, so check the note and ask the servicer before making a large payment.
Sources and methodology
See the official primary source used for this calculator and read Finly’s calculation methodology.
Updated and logic reviewed: September 17, 2026. Results are educational estimates, not financial, tax, legal, or investment advice.