Mortgage refinance break-even: when refinancing actually saves money

Refinancing trades the cost of new loan origination (closing fees, points, appraisal — typically $3,000-6,000 in the US) for a lower interest rate. Whether the trade is worthwhile comes down to one number: the break-even period — how long you have to stay in the new loan for the monthly savings to recoup the upfront costs. Sounds simple. It has four traps.

The simple formula

Standard break-even calculation:

break_even_months = total_refi_costs / monthly_payment_reduction

Worked example. Current mortgage: $400,000 balance at 7%, 25 years left, $2,827/month. New mortgage: same balance and term at 6%, $2,577/month. Refi closing costs: $4,500.

• Monthly payment reduction: $2,827 − $2,577 = $250
• Break-even: $4,500 / $250 = 18 months

If you’ll be in the house at least 18 months, the refi is “worth it” by the simple metric. The trouble is the simple metric is wrong in four common cases.

Trap 1: comparing different loan terms

A common refi pitch resets the clock: refinance from 25 years remaining on the old loan to a fresh 30-year on the new one. The monthly payment drops dramatically because you’ve extended the amortisation, not because the rate is better.

The honest comparison is same term. Old loan 25 years remaining → new loan 25 years. Or compare on total interest paid over a fixed horizon (say, 10 years from now), which captures the term difference.

Trap 2: closing costs rolled into the loan

Many no-cash-out refis roll closing fees into the new loan balance. Your closing-day cash outlay is zero — but you’re paying interest on those costs for the loan’s life. The simple break-even formula ignores this.

For rolled-in costs, compute break-even on the full-amortisation cash flow comparison: old loan’s remaining payments vs new loan’s payments, cumulatively, until the cumulative savings exceed the rolled-in cost. Spreadsheet territory; ballpark, add 20-30% to the simple break-even.

Trap 3: tax effects (mortgage interest deduction)

In the US, mortgage interest is tax-deductible up to certain limits (currently $750k acquisition debt for post-2017 originations). If you take the deduction, your effective interest rate is lower than the nominal — and the break-even from refinancing is correspondingly longer because the deduction shrinks the value of any rate reduction.

Effective rate = nominal × (1 − marginal tax bracket). For a 24% bracket borrower, a 7% mortgage costs 5.3% after deduction; a 6% refi costs 4.56%. The real saving is 0.74 percentage points, not 1. Tax-aware break-even is roughly the simple break-even divided by (1 − marginal rate).

Caveat: only relevant if you itemise. The 2017 standard deduction doubling means most US households take the standard deduction and get no tax benefit from mortgage interest. Check your last year’s tax return before adjusting.

Trap 4: opportunity cost of the closing-day cash

If you pay $4,500 in closing costs out of pocket, that $4,500 isn’t earning anything for the rest of the loan’s life. At a 5% risk-free return, $4,500 over 25 years is worth about $15,250 (compounded). The honest break-even includes the foregone investment return.

Practical shortcut: if your liquid savings are earning 4-5% (high-yield savings, short-term Treasuries), add ~50% to the simple break-even. If you’d otherwise invest the cash long-term (stock index), add 100%+. If you’d otherwise leave it in a 0.01% checking account, the simple break-even is approximately right.

The four-scenario decision matrix

What to compute, in order

1. Real all-in closing costs.Add every line item from the Loan Estimate. Skip the “APR difference” framing — APR is the lender’s summary, you want the cash number.
2. Monthly payment delta at the same term.Use our mortgage calculator to recompute the new payment at the old remaining term.
3. Simple break-even. Closing costs ÷ monthly delta.
4. Adjust for taxes and opportunity cost.Divide by (1 − tax rate) if itemising. Multiply by 1.5× if the closing cash would otherwise earn 5%+.
5. Compare to your expected stay. If the adjusted break-even is shorter than your expected stay minus a safety margin (say, 18 months), refinance.

Walkthrough: a borrower who shouldn’t refinance

Counter-case to the standard worked example. Borrower has $250,000 remaining at 6.75%, 22 years left, $1,872/month. New offer: 6.25% over a fresh 30-year term, $4,800 in closing costs. The pitch: payment drops to $1,539/month — a $333/month saving and a 14.4-month simple break-even.

Recompute honestly. Hold the term: 6.25% over the remaining 22 years gives a $1,793/month payment. The actual rate-driven saving is $79/month, not $333. Break-even at same-term: $4,800 ÷ $79 = 61 months. Then layer trap 4: that $4,800 of closing cash invested at 5% over 22 years compounds to ~$14,000 of foregone return. Adjusted break-even climbs to roughly 90 months — 7.5 years. If the borrower expects to move within 5, the math says skip even though the headline payment drop looked attractive.

Common mistakes

• Treating the new payment as the saving. A $333 monthly drop is mostly term extension, not rate improvement. Same-term comparison is the only honest one.
• Ignoring the principal-already-paid effect. Twelve years into a 30-year mortgage, most of your monthly payment is principal, not interest. Refinancing into a fresh 30 reverses that — you’re back to paying mostly interest. The amortisation reset is invisible in the headline payment.
• Forgetting escrow re-funding.Most refi closings require pre-funding the new escrow account with 2-12 months of property tax and insurance. The original escrow is refunded later, but the closing-day cash hit can be 3-4× what the Loan Estimate shows under “closing costs.”
• Stacking refis. Refinancing twice in five years compounds closing costs; each one needs to break even before the next starts. Two 18-month break-evens 24 months apart is fine; two 30-month break-evens 18 months apart loses money.
• Trusting the lender’s break-even quote. Many lender comparison sheets divide closing costs by the term-extension-driven payment drop, which inflates the apparent savings. Run the calculation yourself with the same term on both sides.

For the related affordability question (how big a mortgage you should carry in the first place), see how much house can I afford. For the term-length decision the refi often raises, see the 15- vs 30-year mortgage comparison.

Sources: Federal Reserve “Consumer’s Guide to Mortgage Refinancing” (2023); CFPB Loan Estimate rule (TRID); J.P. Morgan Asset Management long-term returns reference (2024); Freddie Mac Refinance Analysis (2023).