Mortgage Recast Calculator
See your new lower monthly payment after a lump-sum principal payment — and whether recasting or just paying extra principal is the smarter move for you. Instant, no sign-up, formula shown.
Your balance after recasting
The recast (green) starts lower after your lump sum and is repaid on the same schedule — the gap is the payment relief you get every month.
Recast vs extra principal vs doing nothing
The same lump sum, three ways. Recast lowers your payment; extra principal saves the most interest.
| Strategy | Monthly payment | Payoff time | Interest saved |
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The exact formula — with your numbers
Your new payment is the standard amortization of the reduced balance over the same remaining term:
P = balance after the lump sum · r = monthly rate (APR ÷ 12) · n = remaining months. The rate and payoff date don't change — only the balance, and therefore the payment.
How to use this mortgage recast calculator
- Enter your current balance, rate and years left. These come straight off your latest statement.
- Add the lump sum you plan to pay. Most lenders require a minimum (often $5,000+) to recast.
- Check the comparison. Decide whether lower monthly payments (recast) or less total interest (extra principal) matters more to you.
Recast or extra principal — which wins?
Both start with the same lump sum toward principal. The difference is what happens to your monthly payment. A recast re-amortizes the smaller balance over the same remaining years, so your payment drops and your payoff date stays put — great if you want breathing room in your monthly budget. Paying that same amount as extra principal without recasting keeps your current (higher) payment, which means you knock out the loan years earlier and save considerably more interest. Neither changes your rate. Recasting is for cash flow; extra principal is for getting debt-free faster.
Frequently asked questions
Is a recast the same as a refinance?
No. A refinance replaces your loan with a new one at a new rate, with a credit check and closing costs. A recast keeps your existing loan, rate and term — only the balance and payment change, for a small one-time fee.
Will recasting lower my interest rate?
No. Your rate is unchanged. You save interest only because the balance is smaller, not because the rate improves.
Who should recast?
Homeowners who've come into a lump sum (bonus, home sale, inheritance) and want a lower required payment while keeping their low rate. If your goal is to pay the least interest overall, compare against the extra-principal row above.
Method & sources
- Calculation: Standard mortgage amortization (shown above). The recast re-amortizes the post-lump-sum balance over the same remaining term; the extra-principal comparison keeps the original payment until payoff. Verified against an independent test suite.
- Recast fees and minimums vary by lender (commonly $150–$500 and a $5,000+ minimum). Confirm your servicer's policy before paying.
- Reviewed: · Assumptions reviewed quarterly.
Educational estimate, not financial advice. Confirm figures with your loan servicer.