Identify the decision you are making
Recasting re-amortizes existing debt after a principal contribution. Refinancing replaces a mortgage with new financing. The first path retains the existing rate and remaining term in this model; the second uses a new quote. A recast does not provide a route to a lower market rate.
Hold the lump sum constant
Consider a $300,000 current balance and $40,000 available for principal. Compare recasting $260,000 with refinancing $260,000, before any financed fees. Comparing a recast after the contribution with a refinance of the original $300,000 mixes the financing choice with a different cash commitment.
The comparison calculator therefore applies the same contribution to both options. It tracks recast and refinance fees separately. If you want to preserve more cash through refinancing, model that as a different scenario and explicitly record the cash retained.
Read three results together
First, compare required monthly P&I. Second, compare accumulated interest plus transaction fees over the time you expect to keep the loan. Third, compare the balances still owed at that point. A lower payment can reflect a longer repayment period, and the larger remaining debt is economically relevant.
Principal repayment is not a fee. Including every dollar of principal paid as a cost without crediting the lower balance would penalize faster repayment. The horizon comparison instead focuses on interest and fees while reporting debt separately.
Financed costs still belong in the comparison
If $4,500 of refinance costs are added to the new balance, the borrower avoids paying that amount at closing but owes it as debt. The model counts the fee once as a transaction cost and includes the interest caused by financing it. Counting both the fee and its principal repayment as separate costs would double count it.
Conversely, subtracting a future escrow refund from nonrecoverable fees can overstate savings. Keep escrow timing, loan principal and actual transaction costs in different parts of the worksheet.
Test the holding period before choosing
Run the same two options for a short, middle and long horizon that reflect your plans. The initial fee difference matters more when the loan will be kept briefly. A rate difference has more time to accumulate when the horizon is longer. Neither the future move date nor a future refinance is certain.
After the math, verify that both options are available. Ask the existing servicer about recasting and obtain an itemized refinance quote. The site compares supplied terms; it does not predict approval or negotiate those terms.
Questions, answered
Is the smaller payment always cheaper?
No. Compare interest, fees and remaining balances over the same horizon.
Should the lump sum count as a fee?
No. It reduces debt, although it also reduces liquid cash.
Sources
- Re-amortized (recast) mortgages. Fannie Mae. Accessed 2026-09-09.
- A consumer’s guide to mortgage refinancings. Federal Reserve Board. 2008-08-27. Accessed 2026-09-09. Historical educational resource, used only for enduring comparison concepts, not current pricing or legal requirements.