What a refinance calculator is really deciding
Refinancing swaps one debt for another. You take a new loan, use it to clear the old one, and start paying the new lender instead. Nothing about the house changes. What changes is the interest rate, the number of years left, and — because arranging a mortgage is never free — your bank balance on closing day.
That last part is what makes the decision awkward. A lower rate is obviously good. Paying several thousand dollars for it is obviously bad. The question is never "is the new rate lower?" but "does the lower rate earn back what it cost me before I sell, move, or refinance again?" Everything this calculator prints is aimed at that one question.
There is a second trap underneath it. Most people compare their current payment to the new payment and stop there. But you are not comparing two payments, you are comparing two remaining loans. Someone twenty-two years into a thirty-year mortgage has eight years of mostly-principal payments left. Refinancing that into a fresh thirty-year term will cut the monthly payment dramatically and still cost a fortune, because it stretches an almost-finished debt back out over three decades. This tool always measures your current loan by what is left on it, never by what it looked like the day you signed.
The formulas behind the numbers
Both loans are ordinary amortizing loans, so both use the standard payment formula. With P as the balance, i as the monthly rate (annual rate divided by twelve) and n as the number of monthly payments:
If you told us the balance and the payment instead of the term, we run that backwards to find how many payments you have left:
The remaining balance at any month t — which is what makes the equity comparison possible — is the original balance grown by interest, minus the future value of the payments made so far:
The APR is the only figure that needs solving numerically. It is the interest rate at which the money you actually receive — the new loan minus the points and fees you hand over — produces exactly the payment schedule you have agreed to. There is no closed-form solution, so the calculator narrows it down by bisection until it is accurate well beyond the third decimal place we display.
Lifetime saving is then the total of everything you would still have paid on the old loan, minus everything you will pay on the new one, plus any cash you took out, minus the upfront cost.
What to put in each field
Two tabs describe the same loan from different directions. Use whichever matches the paperwork in front of you.
- I know my balance. Take the payoff balance from your most recent statement and the principal-and-interest portion of your payment. This is the accurate route, because a payoff balance is a fact rather than an estimate.
- I know the original loan. Enter what you borrowed, the term you signed up for, and roughly how much time is left. The calculator reconstructs the payment and works the balance forward from there.
- Monthly payment must be principal and interest only. The escrow portion that covers property tax and homeowners insurance is not part of the loan — those bills follow the house and carry on unchanged after a refinance. Including them inflates your apparent saving.
- Discount points are entered as a percentage of the new loan. One point is one percent, paid at closing, in exchange for a lower rate.
- Costs and fees covers everything else due at closing: origination, appraisal, title search and insurance, recording, credit report, and the lender's own administrative charges.
- Cash out amount is any extra you borrow beyond clearing the old loan. Leave it at zero for a plain rate-and-term refinance.
Why the usual break-even formula gives the wrong answer
Almost every article on refinancing gives you the same rule: divide the closing costs by the monthly saving. Spend $3,960 to save $253.55 a month and you break even in sixteen months. It is simple, it is memorable, and it is wrong often enough to matter.
What it ignores is that the two loans repay principal at different speeds. Every month, part of each payment buys equity. If the new loan is at a lower rate, a larger share of the same payment goes to principal, so you are building ownership faster as well as paying less. That equity is real money — you get it back when you sell — and the simple formula throws it away entirely.
This calculator counts it. Break-even here is the first month where cumulative payment savings, plus the gap that has opened up between the two balances, finally exceeds what you paid upfront. Using the figures the page loads with, the naive method says sixteen months. Counting equity, you are genuinely ahead in twelve.
The gap can be far wider than that. Take a loan where the payment barely moves — a borrower swapping a long, high-rate balance for a much shorter, cheaper one might save only a few dollars a month while cutting years off the term. Divide the closing costs by that tiny monthly saving and the arithmetic will tell you it takes sixty years to break even, which is nonsense: the refinance is excellent, and the payback arrives inside three years once the faster principal repayment is counted. Any time the new term is shorter than the old one, treat the simple formula as actively misleading.
Rate versus APR: what points actually buy
The interest rate sets your payment. The APR tells you what the loan costs once the fees are folded in, which is why federal disclosure rules require lenders to quote it. A 5.875% rate that costs $3,960 to obtain behaves, over twenty-five years, like a loan at roughly 6.009% with no fees at all.
That is the honest way to compare two quotes. A lender advertising a headline rate half a point below everyone else has usually bought that number with points, and the APR is where it reappears. When you put two Loan Estimates side by side, compare APR to APR — and compare both against the rate you are paying now, which is what the verdict line at the top of the result card does.
Whether points are worth buying depends entirely on how long you keep the loan. Points are prepaid interest: you hand over money now to reduce every payment afterwards. Keep the mortgage long enough and that trade is profitable. Sell in four years and you have simply donated the money. The longer you are certain you will stay, the more sense points make.
Shorter term or smaller payment — usually you pick one
Refinancing can lower your monthly payment or get you out of debt sooner. Doing both at once requires a genuinely large drop in rate, which is why most borrowers end up choosing.
Resetting to a fresh thirty-year term produces the biggest drop in monthly cost, and if cash flow is tight that is a perfectly rational thing to want. The price is total interest. Restarting the clock means paying interest on a shrinking balance for longer, and if you are well into the current loan it can wipe out the benefit of the lower rate completely — the total-interest row in the comparison table will show that plainly.
Shortening the term does the opposite. Moving from what is left of a thirty-year loan into a fifteen-year one usually raises the payment, sometimes sharply, but the interest saving is large and shorter terms are normally priced below longer ones. Try a few terms in the new-loan field and watch the total-interest row rather than the payment row; that is where the real difference shows up.
Cash-out refinancing changes the question
A cash-out refinance borrows more than you owe and hands you the difference. The new loan is your balance plus the cash, so the payment rises and the points, being a percentage of a bigger loan, cost more too. The calculator handles this: enter the amount and the cash is credited back in the lifetime figure, because money in your pocket is not a loss.
What it cannot tell you is whether the trade is wise. You are converting home equity into cash and agreeing to pay mortgage interest on it for decades. That is cheap money compared with credit cards, and it is secured on your home, which is precisely the risk — unsecured debt does not cost you the house if things go badly. Note also that when you take cash out, the monthly payment usually rises, so there is no payment saving to recover the costs from and the break-even line stops being meaningful. Judge a cash-out on what the money is for, not on the break-even month.
What this calculator does not cover
Being clear about the edges matters more than pretending there are none.
- Taxes. Mortgage interest is deductible for some filers and not others, and points on a refinance are generally deducted gradually across the life of the loan rather than all at once. Nothing here is adjusted for tax.
- Escrow, PMI and insurance. Only principal and interest are modelled. If a refinance removes mortgage insurance because your equity has grown past twenty percent, that is a real saving this page does not show — and a real reason your quoted total may look better than the figures here.
- Rolled-in costs. This assumes you pay closing costs out of pocket. If you finance them instead, add them to the balance and set the fees to zero to model it properly.
- Adjustable rates. Both loans are treated as fixed. An ARM's payment after the initial period depends on an index nobody can forecast.
- Prepayment penalties on the loan you are leaving, and the opportunity cost of the cash you spend at closing.
- Whether you qualify. Rates depend on credit score, equity, occupancy and loan type. The rate you are quoted may not be the rate you are offered.
Frequently asked questions
Is it worth refinancing to save $100 a month?
It depends entirely on what it costs and how long you stay. Saving $100 a month against $4,000 in closing costs takes roughly three years to recover on payments alone, and less once faster principal repayment is counted. If you are confident you will keep the house well past that point it is worth doing; if you might move within a couple of years it is not. The old advice about needing a full one-percent rate drop is outdated — on a large balance a quarter-point can pay, and on a small one a full point sometimes does not.
How do I calculate my refinance break-even point?
The quick version is closing costs divided by monthly saving, which gives you the number of months to recover the cost. The accurate version also counts the equity difference, because a lower rate or shorter term repays principal faster and that gain is yours too. This calculator uses the accurate version, which is why its break-even month is usually earlier than the simple division suggests.
Does refinancing restart my 30-year mortgage?
Only if you choose a thirty-year term again, which is the default most lenders quote. You are free to pick a term close to the time you have left, and doing so keeps your original payoff date roughly intact while still capturing the lower rate. Compare the total-interest row for each option rather than the payment; a shorter term nearly always wins there.
Should I pay points to lower my refinance rate?
Points are worth buying when you will hold the loan long enough for the reduced payments to exceed what the points cost, typically somewhere between five and ten years. If there is any real chance you will sell or refinance again before then, take the higher rate and keep the cash. Compare the APR of a with-points quote against a no-points quote from the same lender to see what you are actually buying.
What are typical closing costs on a refinance?
Most refinances land between two and six percent of the loan amount once origination, appraisal, title work, recording and lender fees are added up. Your Loan Estimate lists every line, and lenders are required to send you one within three business days of applying. Title and appraisal charges are often negotiable or transferable, so it is worth asking.
Is a no-closing-cost refinance actually free?
No. The lender either builds the costs into a higher interest rate or adds them to your balance, so you pay either way — just gradually instead of at closing. It can still be the better deal if you expect to move within a few years, since you never reach the break-even point where paying upfront would have won. Compare the APRs and the arrangement stops looking free very quickly.
Does a cash-out refinance change the break-even math?
Yes, and usually it removes it. Borrowing more raises the monthly payment, so there is no payment saving from which to recover the closing costs, and the break-even line no longer applies. What matters instead is whether the interest you will pay on the extra borrowing is worth what you are spending the money on.
How soon after buying can I refinance?
Conventional loans often allow it immediately, though many lenders impose a seasoning period of six to twelve months, and government-backed refinance programmes have their own waiting rules. The practical constraint is rarely the calendar — it is that closing costs come round again, so refinancing twice in quick succession means paying twice for the privilege.
This calculator produces estimates for general information only and is not financial, tax, mortgage or legal advice. Results depend entirely on the figures you enter and on assumptions that may not match your loan. Only your lender's Loan Estimate and Closing Disclosure show the terms you are actually being offered. Before refinancing, speak to a licensed mortgage professional or a qualified financial adviser about your own circumstances.