Mortgage Recast Calculator
A recast applies a lump sum to your principal and re-amortizes the loan to a lower payment — same rate, same payoff date. Most calculators ignore it entirely. This one models it, then shows how it stacks up against simply prepaying.
Open the recast calculator →Free and instant. Enter your balance and lump sum to see the new payment.
How a recast works
You pay a large amount toward principal, and the lender recalculates (re-amortizes) your monthly payment across the original remaining term on the new, smaller balance. You keep your interest rate — valuable when it's lower than today's — and pay only a modest recast fee. The result is a permanently lower required payment without the cost or paperwork of a refinance.
Recast vs. prepay: two ways to use the same cash
- Recast — lowers the monthly payment, keeps the original payoff date. Best for cash-flow relief.
- Prepay — apply the lump sum but keep paying the old amount, so the loan ends sooner and saves more interest overall.
| Balance — $300,000 at 6.5%, 28 years left | $1,941/mo |
| Lump sum applied to principal | $50,000 |
| New payment after recast | $1,618/mo |
| Payment drop | $323/mo |
| Interest saved (recast) | ~$58,700 |
Keeping the old $1,941 payment instead (prepay, no recast) would pay the loan off in about 18½ years and save roughly $172,000 — more interest, but no monthly relief. Same $50,000, two very different goals.
Common questions
What is a mortgage recast?
A lump-sum principal payment after which the lender recalculates your payment over the original remaining term. Rate and payoff date stay; the payment drops. Fees are typically $150–$500.
Recast or refinance?
Recast keeps your current rate for a small fee — ideal when your rate is good. Refinance swaps in a new rate/term with full closing costs, better only if rates have dropped significantly.
Recast or just prepay?
Recast lowers the payment; prepaying keeps it and pays off sooner, saving more interest. The calculator shows both side by side.