Mortgage recast calculator with amortization schedule
Estimate the required monthly principal-and-interest payment after a lump-sum reduction of your outstanding mortgage balance. A recast re-amortizes the smaller balance at the same rate over the same remaining contractual term. This mortgage recast calculator with amortization schedule also compares making the same lump sum while keeping the original modeled payment.
The three scenarios answer different questions: make no change; pay the lump sum and recast; or pay the lump sum without recasting. Recasting can lower the required payment. Keeping the higher payment can pay off the balance sooner and reduce interest further. This page calculates both outcomes rather than treating them as the same choice.
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Optional mortgage and personal finance books (paid link) can help explain the difference between a lower required payment and a shorter payoff period. No purchase is necessary to use the calculator.
How to calculate a mortgage recast
- Enter your outstanding principal, currency label and fixed annual rate.
- Enter the remaining contractual years and additional months, not the original full loan term.
- Enter the lump sum to apply immediately before the first modeled monthly payment.
- Add a separately paid recast fee and optional monthly extra principal if you want to test them.
- Compare the three scenarios, select a schedule and switch between monthly and annual views. Download CSV for every row of every scenario.
The original P&I payment is modeled from the entered balance, rate and remaining term. It is not read from a lender statement. Previous extra payments, fees or servicing adjustments can make your actual contractual payment differ. Use a lender quote to confirm the precise recast timing and payment.
Keep those source records together; optional document organizers (paid link) can help organize the latest statement and recast quote.
Mortgage recast formula and monthly payment
M = P × r ÷ [1 − (1 + r)−n]
P is the principal to amortize, r is the annual nominal rate divided by 100 and by 12, and n is the remaining number of monthly payments. The same rate and contractual term are used before and after the recast. At 0% interest, M = P ÷ n. The upfront fee is not financed and does not increase the new balance.
For example, a balance of USD 300,000 at 6% with 25 years remaining has a modeled monthly P&I payment of about USD 1,932.90. After a USD 50,000 lump sum, the required payment becomes about USD 1,610.75. The required monthly reduction is about USD 322.15 before optional extra principal.
For an independent arithmetic check, optional financial calculators (paid link) can help evaluate the payment formula. Displayed values are rounded to cents while the schedule retains precision, so multiplying a displayed monthly payment by the number of months may not reproduce the exact final total.
Recast versus extra payments without recasting
In the no-action scenario, there is no lump sum, fee or extra monthly principal. In the recast scenario, the lump sum reduces principal now and the entered fee is paid separately. Optional extra principal is then added to the recalculated payment. In the no-recast scenario, the same lump sum and same optional extra principal are used, but the original modeled monthly P&I payment is retained and no recast fee is charged.
The payment reduction compares required P&I amounts, not chosen cash outflows. A large extra monthly payment can make your planned outflow exceed the original required payment even though the recast minimum is lower. Net savings versus no action subtracts total future cash costs, including the lump sum and fee, without discounting cash flows. A negative figure means the entered recast plan costs more on that basis.
Optional budget planners (paid link) can help record both the required payment and the amount you actually plan to pay. For general extra-payment schedules, use the Amortization Calculator. To model replacing a mortgage with another rate or term, use the Refinance Calculator.
Scope, eligibility and what the schedule excludes
This is a fixed-rate, equal-month educational model, particularly relevant to US mortgage-recast planning. It does not decide whether a lender or loan program permits recasting, set a required lump-sum minimum, or guarantee fee amounts. A lender may apply the lump sum on a different date, accrue daily interest, round monthly amounts or require additional steps.
Principal supports up to 1 billion currency units; annual rates range from 0% to 50%; the remaining term is 1–600 months. Money accepts up to two decimals and rates up to eight. The lump sum may be zero for a comparison but must be below the balance; a full payoff is outside this recast model. Optional fees support up to 100,000 and extra monthly principal up to 10 million. Enter plain numbers without symbols or commas.
Taxes, insurance, escrow, PMI changes, prepayment penalties, variable rates, future lump-sum dates and opportunity cost of cash are excluded. The schedules start with modeled month 1 rather than calendar dates. Currency labels do not convert money or apply national lending rules. For ownership costs use the Mortgage Calculator. For interest-only and balloon structures use the Interest-Only Mortgage Calculator.
Mortgage Recast Calculator FAQs
Sources and methodology
Independent educational monthly-payment model, reviewed October 21, 2026. These sources explain the product structures. The site is not affiliated with the lenders, agencies or publishers. Assumptions and exclusions are stated above.