How this instrument works
A mortgage refinance replaces the loan you have with a new one against the same balance, at whatever rate and term a lender is currently willing to offer. This instrument runs the standard amortizing-payment formula twice — once against Current rate, % and Remaining years on current loan, once against New (refinance) rate, % and New loan term, years — and reports Monthly payment savings as the gap between the two results. Because New loan term, years is set independently of what is left on the current loan, the comparison folds together two separate effects: whatever the rate drop alone is worth, plus whatever spreading the same balance over a longer or shorter clock is worth on its own.
Break-even period, months exists because a refinance is not free — Refinance closing costs, $ covers the new lender's origination, appraisal, and title work, and that money has to be earned back in savings before the swap is worth anything. Dividing the fee by Monthly payment savings gives the exact month that happens. A homeowner who expects to stay in the house well past that point comes out ahead; the common mistake is refinancing right before a move or another refinance, which locks in the fee without enough months left to recover it — the same $4,000 that would pay for itself in fifteen months instead becomes a straight loss.
The figure has real limits. It assumes Refinance closing costs, $ are paid in cash rather than rolled into the new loan balance, and it compares monthly cash flow rather than total interest paid over the life of either loan — a longer New loan term, years can lower the payment and still cost more in interest across the full term, because amortization restarts and the early payments go mostly to interest again, the way they did on the original loan. It also leaves out anything not tied directly to closing, such as a rate lock fee, prepaid interest for the days before the first new payment is due, or a change to escrowed property tax and insurance.
- Enter Current balance, $, Current rate, %, and Remaining years on current loan exactly as your latest mortgage statement shows them.
- Enter the offer under New (refinance) rate, % and New loan term, years — the term the new loan starts counting from zero.
- Enter Refinance closing costs, $, the fees the new lender charges to originate and close the loan.
- Compare Current monthly payment against New monthly payment, and read Monthly payment savings for the exact monthly difference.
- Check Break-even period, months against how many more months you expect to keep the loan before deciding.
Worked example — refinancing $250,000 from 7% to 6%
Take a homeowner who owes $250,000 (Current balance, $) at 7% (Current rate, %) with 25 years remaining (Remaining years on current loan) — the amortizing-payment formula returns a current payment of $1,766.95, matching the figure their existing loan statement already shows.
A lender then quotes 6% (New (refinance) rate, %) on a fresh 30-year loan (New loan term, years), against $4,000 of closing costs (Refinance closing costs, $). Running the same formula at the new rate and the new, longer term returns a new payment of $1,498.88 — a Monthly payment savings of $268.07 a month. Dividing the $4,000 fee by that monthly figure gives a Break-even period, months of 14.92, under fifteen months. Anyone planning to keep this loan past that point comes out ahead; someone selling or refinancing again before then hands the $4,000 back to the lender out of savings that never fully materialized.
Questions
Why does the new loan term matter separately from the new rate?
New loan term, years is set independently of Remaining years on current loan, so part of the drop in New monthly payment can come from spreading the same balance over more months rather than from the lower rate alone. In the default numbers here, the loan resets from 25 years remaining to a fresh 30, so some of the $268.07 Monthly payment savings is a term effect blended in with the rate effect. Set New loan term, years to match Remaining years on current loan to isolate what the rate drop alone is worth.
What does a negative Break-even period, months mean?
It means the new offer costs more per month than the current loan, not less. Monthly payment savings comes out negative because New monthly payment exceeds Current monthly payment, and dividing a positive Refinance closing costs, $ figure by a negative savings figure produces a negative months count — the arithmetic's way of flagging that this refinance never earns back its own fees and only gets more expensive the longer the loan runs.
Should closing costs rolled into the new loan be entered the same way as cash paid at closing?
Not exactly. This sheet assumes closing costs are paid out of pocket, since New monthly payment is computed on the same Current balance, $ as the old payment. If a lender instead rolls Refinance closing costs, $ into the new loan, the real balance being financed is larger than what is entered here, New monthly payment runs slightly higher than shown, and Break-even period, months understates how long the fees actually take to earn back.
How long should I plan to keep the loan before refinancing pays off?
The instrument does not decide that — only Break-even period, months, the point where accumulated Monthly payment savings equals Refinance closing costs, $. At 14.92 months in the default example, someone who expects to hold the loan for several more years clears that mark easily; someone likely to sell or refinance again within a year would pay the $4,000 in fees and recover less in savings than the fees cost. Comparing that number against how long you actually expect to stay is the judgment call the sheet stops short of making.
Does the lower monthly payment mean I will pay less interest over the life of the loan?
Not necessarily. New monthly payment can fall from a lower New (refinance) rate, %, a longer New loan term, years, or both together, and a longer term restarts amortization from month one, so a large share of each new early payment goes to interest again, the way it did when the original loan was new. A lower rate paid over more months can still add up to more total interest than a higher rate paid over fewer of them; this sheet reports the monthly cash-flow gap and the break-even point, not lifetime interest.
References
- CFPB — Owning a Home
- Federal Reserve — Consumer's guide to mortgage settlement costs
- IRS — Publication 936, Home Mortgage Interest Deduction
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.