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Recast vs Paying Extra on a Low-Rate (3%) Mortgage

Published October 14, 2026 · By the PrepayMath team

Not financial advice. This guide is for general education only. Examples use simplified assumptions (fixed rates, principal and interest only) and are not recommendations or rate quotes. Confirm details with your loan servicer, lender, or a licensed financial or tax professional before acting.

Millions of homeowners locked in mortgage rates around 3% when rates were low. With current market rates far higher (Freddie Mac's survey put the average 30-year fixed rate at 7.40% for the week of October 8, 2026 ^[source]), that cheap loan is valuable. So if you have spare cash, should you recast, pay extra, or leave the mortgage alone? This guide runs the numbers for a 3% loan and shows why a low rate changes the answer.

The setup

You owe $250,000 at 3% with 24 years left. Your principal and interest payment is $1,218.77, and over the remaining term you'd pay about $101,007 in interest if you change nothing.

Option 1: Recast with a $40,000 lump sum

You send $40,000 to principal and pay a $250 recast fee. The servicer re-amortizes the balance over your remaining 24 years at the same 3% rate. Fannie Mae's servicing rules describe a recast this way: the principal and interest payment is reduced based on the current balance, the current interest rate and the remaining loan term. ^[source]

• New payment: $1,023.77, which is $195.00 less a month
• Interest saved after the fee: about $15,911

Option 2: Pay the $40,000 and keep your payment

Same $40,000, no recast, and you keep paying $1,218.77:

• Paid off in about 18 years 10 months, more than five years early
• Interest saved: about $35,974 (about $35,724 if you count the $250 you'd otherwise have spent on a recast)

How the low rate changes things

Compare the same $40,000 on the same balance at 6.5%. Recasting would save about $38,840 in interest and lower the payment by $274.62. Paying extra and keeping the payment would save about $108,975. At 3%, the interest saved is a fraction of that, because there's less interest to avoid in the first place.

That's the key point for low-rate borrowers. Every dollar you put into a 3% mortgage earns a guaranteed 3%. That's a real, risk-free return, but it's a modest one. The question is whether you have a better use for the money.

Prepaying vs investing on a 3% loan

Suppose instead of a lump sum you have $300 a month extra. We compared prepaying (then investing the freed-up payment after the loan is gone) with investing the $300 from the start, over the remaining 24 years, with a 15% tax on investment gains. Prepaying clears the loan in about 17 years 9 months.

With no tax and a 3% return, the two paths tie exactly (about $126,311 each). That's the break-even: your mortgage rate. Add a 15% tax on gains and prepaying edges ahead at 3%. Above about 4%, investing pulls ahead, and the gap grows quickly with higher returns.

Two caveats. First, these returns are held steady every year. Real investments rise and fall, and Investor.gov describes risk tolerance as your ability and willingness to lose some or all of your original investment in exchange for potentially greater returns. ^[source] Second, taxes matter. The IRS says the tax rate on most net capital gain is no higher than 15% for most individuals, and some gains are taxed at 0%. ^[source] Investing through retirement accounts can change the math. If you itemize, the mortgage interest deduction can lower your effective mortgage rate a little further. ^[source]

So which should a 3% borrower choose?

Recast if…

• You already decided to put a lump sum into the house and want the lowest required payment while keeping your rate.
• Cash flow matters more to you than interest savings. A $195 lower payment is permanent flexibility.

Pay extra and keep your payment if…

• You want to be mortgage-free sooner, with a guaranteed return and no market risk.
• You'd otherwise leave the money in cash earning less than your mortgage rate after tax.

Leave the mortgage alone if…

• You can reliably invest the money and expect to earn more than 3% after tax over the long run.
• You value liquidity. Invested money can be sold if needed, but home equity is hard to reach.

Don't skip the basics

Whatever you choose, keep an emergency fund. The CFPB notes that people without savings often fall back on credit cards or loans when something unexpected happens, and that debt is usually far more expensive than a 3% mortgage. ^[source] Paying off high-interest debt first almost always beats prepaying a low-rate loan.

A note on refinancing

With a 3% rate and market averages well above that, refinancing would almost certainly raise your rate. That's why recasting is so popular with low-rate borrowers: it lowers the payment without giving up the rate. If you need a lower payment and have a lump sum, a recast is usually the only practical route.

Common mistakes on low-rate loans

• Prepaying with your emergency fund. The guaranteed 3% isn't worth being cash-poor.
• Assuming investing always wins. After a 15% tax and at a 3% return, prepaying came out slightly ahead in our example. The answer depends on your real return and taxes.
• Refinancing to "get cash out" at a much higher rate without comparing alternatives.
• Recasting when you didn't need a lower payment. If cash flow isn't an issue, simply prepaying (or not prepaying at all) may fit better.

A quick way to decide

1. Write down your mortgage rate. That's the guaranteed return on every prepaid dollar.
2. Estimate a realistic after-tax return on the alternative, whether that's savings, a retirement account or a taxable brokerage account.
3. If the alternative clearly beats your mortgage rate after tax and you're comfortable with the risk, investing is likely the better long-run choice.
4. If not, or if being debt-free matters a lot to you, prepay. Recast only if you also want the lower required payment.
5. Re-run the numbers whenever your income, tax situation or savings change.

The bottom line

On a 3% mortgage, recasting is a good way to lower your payment while keeping your valuable rate, and paying extra gives a modest but guaranteed 3% return. Whether either beats investing depends on your after-tax return and risk tolerance. Run your numbers both ways before you decide.

Compare prepaying vs investing on your low-rate loan →

Not financial advice. This guide is for general education only. Examples use simplified assumptions (fixed rates, principal and interest only) and are not recommendations or rate quotes. Confirm details with your loan servicer, lender, or a licensed financial or tax professional before acting.