Recasting an interest-only mortgage means making a large principal payment and then re-amortizing the remaining balance over the rest of the term, which lowers your future principal-and-interest payment. It is the single most powerful lever for softening the payment jump that hits when the interest-only period ends, because a smaller balance spread over the same remaining years produces a smaller monthly payment.
This guide shows exactly how a recast changes the numbers, when it is worth doing, and how to plan one. Run your own figures in the Interest-Only Mortgage Calculator as you read.
Why an interest-only loan needs help when the IO period ends
During the interest-only (IO) window, your payment only covers interest, so the balance never drops. On a $400,000 loan at 7.0% with a 10-year IO period, the monthly payment is just the interest:
- IO payment: $400,000 x (0.07 / 12) = $2,333.33
- Balance after 10 years: still $400,000 (you paid $280,000 in interest and reduced principal by $0)
When the IO period ends, the full $400,000 must be paid off over the remaining 20 years as a normal amortizing loan. That full principal-and-interest (P&I) payment is much higher:
- Full P&I payment (20-year amortization of $400,000 at 7.0%): $3,101.20
- The jump: $3,101.20 - $2,333.33 = $767.86 more per month, about a 32.9% increase
A recast attacks that jump at its source: the balance being amortized.
What a recast actually does to the math
A recast does not change your interest rate or your remaining term. It changes only the principal that gets re-amortized. Suppose that over the IO years you save aggressively and make a $50,000 lump-sum payment, dropping the balance from $400,000 to $350,000 right before P&I begins. The lender re-amortizes $350,000 over the remaining 20 years:
| Scenario at start of P&I period | Balance amortized | Monthly P&I (20 yr, 7.0%) |
|---|---|---|
| No recast | $400,000 | $3,101.20 |
| Recast after $50,000 lump sum | $350,000 | $2,713.55 |
The recast cuts the P&I payment by $387.65 per month. Compared with the old IO payment of $2,333.33, the jump shrinks from $767.86 to just $380.22 - roughly half the shock.
Recast vs. a standard refinance
A recast and a refinance both lower a payment, but they work differently:
| Recast | Refinance | |
|---|---|---|
| New loan? | No - same loan | Yes - replaces the loan |
| Rate change? | No | Yes (new market rate) |
| Closing costs | Small flat fee (often a few hundred dollars) | Typically 2%-5% of the loan |
| Requires a lump sum? | Yes | No |
| Credit re-check? | Usually no | Yes |
If your current rate is already attractive, a recast keeps it while shrinking the balance - something a refinance cannot do without resetting your rate to today's market.
When recasting an interest-only loan makes sense
Recasting fits a specific profile, and an IO borrower often matches it:
- You have or expect a lump sum. Bonus-based income, a maturing investment, equity from a sale, or steady extra savings all give you cash to throw at principal. Project that growth with the Savings Goal Calculator or the Future Value Calculator.
- Your interest rate is good. Recasting preserves a low rate that refinancing would lose.
- You want a lower payment, not a faster payoff. A recast lowers the required monthly payment; it does not, by itself, shorten the term.
It is a poor fit if you have no lump sum to contribute, if current rates are far below your rate (refinance instead), or if your lender does not permit recasting an interest-only product - many do not, so confirm in writing before you rely on it.
How to plan and execute a recast
Use the steps below to set up a recast before your IO period ends.
The trade-off to weigh first
Money used to recast is locked into your home and earns the loan's rate as a guaranteed return rather than staying liquid. At 7.0%, paying down principal is the equivalent of a 7.0% pre-tax, risk-free return - strong, but the cash is no longer available for emergencies. Keep a separate emergency cushion intact; size it with the Emergency Fund Calculator before committing a lump sum. According to the Consumer Financial Protection Bureau, you should always confirm loan-modification terms in writing before paying down principal, because not every loan allows a recast.
Bottom line: a recast cannot create equity out of thin air, but if you have the cash, it is the cleanest way to defuse the payment shock baked into every interest-only loan.
Try it yourself
Run your own numbers in the free Interest-Only Mortgage Calculator — instant, private, no sign-up.
Open the Interest-Only Mortgage Calculator →Frequently asked questions
- Does recasting an interest-only mortgage lower my interest rate?
- No - a recast keeps your existing interest rate and term and only re-amortizes a lower balance. On a $400,000 loan at 7.0% with a 20-year payoff, dropping the balance to $350,000 via recast cuts the P&I payment from $3,101.20 to $2,713.55, but the 7.0% rate is unchanged. To change the rate, you would need to refinance.
- How much does a recast cost compared to refinancing?
- A recast usually costs a small flat fee, often a few hundred dollars, while a refinance typically costs 2%-5% of the loan amount in closing costs. On a $400,000 balance, a refinance could run $8,000-$20,000, whereas a recast fee is a tiny fraction of that. The trade-off is that a recast requires you to bring a lump sum of principal.
- Can every interest-only loan be recast?
- No - many lenders do not allow recasting on interest-only products, so you must confirm eligibility in writing before counting on it. Always ask your servicer for the recast policy, minimum lump-sum requirement, and fee before you make a large principal payment, because an unexpected principal payment without a recast simply lowers your balance without re-lowering the required monthly payment.
- Will a recast shorten my loan term?
- No - a recast lowers your required monthly payment but keeps the same remaining term, so it does not speed up payoff on its own. If you want to pay off faster, keep making the higher original payment after the recast; the extra now goes entirely to principal. You can model that effect with the extra-payment mortgage calculator.
- Is it better to recast or just make extra payments during the interest-only period?
- It depends on your goal: extra payments during the IO period lower the balance that gets amortized, and a formal recast then resets the required payment to match that lower balance. Extra payments alone reduce future interest but do not reduce the contractual P&I payment unless you recast. Combine both - pay down principal early, then recast right before P&I begins for the biggest payment relief.
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