Best Mortgage Recast Calculator: What to Check

A good recast calculator takes your balance minus the lump sum, keeps your rate and the months you have left, and returns the new principal and interest payment. Run the test loan below: on $300,000 at 4.5% with 25 years left, a $50,000 lump sum should take the payment from $1,667.50 to $1,389.58.

If a calculator gets that wrong, skip it. If it gets it right, the seven checks decide which one fits your question. The free mortgage recast calculator is on this page too.

Seven checks for any recast calculator

  1. The formula. Payment = P x i x (1+i)^n / ((1+i)^n - 1) on the new balance, with the same rate. See how to calculate a recast payment.
  2. Months left, not the original term. A 30-year loan with 25 years left needs 25, not 30.
  3. The lump sum comes off the balance. A recast is a payment to principal first, then a new payment.
  4. The fee stays separate. A fee is a one-time charge. It does not lower the balance.
  5. Escrow is left out or shown on its own. A recast changes principal and interest only.
  6. It says what the savings are measured against. Against keeping the old payment, or against paying extra. See recast vs extra principal payment.
  7. No sign-up wall. You need four numbers and a result, not an email address.

Test loans with the right answers

Enter each row into any calculator. The new payments below come from the same formula as the calculator on this page. They leave out escrow and any fee.

BalanceRateYears leftLump sumPayment nowPayment after
$300,0004.5%25$50,000$1,667.50$1,389.58
$400,0006.5%28$60,000$2,588.06$2,199.85
$200,0003.25%18$20,000$1,224.23$1,101.81

A difference of a few cents is rounding. A difference of a few dollars means the calculator used another term or another rate.

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What no calculator can tell you

  • Bank of America says it cannot give an estimate of the new payment before the recast is done.
  • Chase's recast page links to a savings calculator in Chase MyHome.
  • Whether your loan is eligible at all. Eligibility depends on your servicer and investor, so ask.
  • Your fee. Ask for it in writing, then use the cost and break-even guide.

Use a calculator to decide whether a recast is worth asking for. Use your servicer's agreement for the real number. To see the same lump sum against a refinance, use the recast vs refinance calculator.

Frequently asked questions

Which mortgage recast calculator is the best?

The best one is the one that passes the seven checks above and matches your servicer's figure once the recast is done. Any calculator that uses the standard loan formula on the smaller balance gives the same principal and interest payment, so the differences are in what it shows around that number.

Is a lender's own calculator more accurate?

Not for the payment itself. The payment comes from the same formula everywhere. A lender can know details you cannot, such as your exact balance and months left. Chase's recast page links to a savings calculator in Chase MyHome.

Can a calculator tell me my exact new payment?

No. Bank of America says it cannot give an estimate of the new payment before the recast is done. A calculator gives an estimate of principal and interest only. Your servicer's agreement has the real figure.

Does the calculator include the recast fee?

This page's calculator does not have a fee box. The fee is a one-time charge, so it is handled apart from the payment. See how much a recast costs for the break-even math.

Why do two calculators give different savings?

Usually one counts the interest saved against keeping the old payment and the other against paying extra. Check which comparison it uses before you trust the savings number.

Sources

Every figure on this page comes from the pages below. Checked 2026-10-20. Rules change, so confirm with your own servicer.

More recast guides