Refinance Math: Break-Even, Term Resets, and "No Closing Cost"

The refinance pitch is always framed the same way: your payment goes down by this much, and here is how many months until the closing costs pay for themselves. That calculation is real, and it is also the easiest way to lose tens of thousands of dollars while feeling like you won.

Here is the full math, run on one loan.

The loan

A $355,000 mortgage at 7.125% on a 30 year term. Principal and interest come to $2,391.70 a month. Three years in, after 36 payments, the balance is $343,643 with 324 payments left.

Do nothing and the remaining interest on that loan is $431,268. Hold onto that figure, because it is the only fair thing to compare against.

The naive break-even

Refinance the $343,643 into a new 30 year at 5.99% with $6,400 in closing costs. The new payment is $2,058.10.

Monthly savings: $333.60. Break-even: $6,400 divided by $333.60 equals 19.2 months. Stay in the house past month twenty and you are ahead. Every calculator on the internet stops here.

What the naive version misses

You just replaced 27 remaining years with 30 new ones. The clock reset, and mortgage amortization is front loaded, so those first years of the new loan are mostly interest again.

Total interest on the new 30 year loan: $397,275 against the $431,268 you were on the hook for. So it still wins here, by about $34,000, but by a lot less than "$333 a month forever" implies. And that margin is entirely because the rate drop was over a full point.

Two better structures on the same rate:

That last row is the one to notice. Take the 30 year loan for the flexibility of a lower required payment, then keep writing the check you were already writing. The loan is gone in 254 months instead of 324, and the interest bill drops to $263,044. Against doing nothing that is $168,224 saved and five years and ten months off the term, from a decision that costs you nothing you were not already paying.

When a lower rate loses money

Now move the same borrower 21 years into the loan. The balance is $190,275, there are 9 years left, and the remaining interest is only $68,028 because they are deep in the principal heavy part of the schedule.

Refinance that into a new 30 year at 5.99% and the payment falls from $2,391.70 to $1,139.57. A $1,252 a month drop. It looks like the best deal anyone has ever been offered.

Total interest on that new loan: $219,971. They just signed up to pay $151,943 more interest in exchange for a lower rate.

The honest version for that borrower is a 9 year term at 5.99%: a payment of $2,283.46, total interest of $56,338, a saving of about $11,690. Smaller headline, actual money.

The rule underneath: never compare payments across different terms. Compare total interest over the same horizon, or compare payments only at the same remaining term.

What "no closing cost" really means

There is no such thing as a free refinance. A no cost loan is a higher rate, and the lender uses the extra interest to fund a credit that pays your costs. It is a trade, and you can price it.

Our lender offers 5.99% with $6,400 in costs, or 6.375% with zero costs. The 6.375% payment is $2,143.89 against $2,058.10, so the paid version saves $85.79 a month. Divide $6,400 by $85.79 and the break-even between the two offers is 74.6 months, just over six years.

Under six years in the house or expecting to refinance again, take the no cost loan. Staying fifteen years, pay the costs. The other flavor of no cost, rolling the $6,400 into the balance, is not free either: you finance it for 30 years at the mortgage rate.

Points, same arithmetic

One point on $343,643 is $3,436 and buys roughly 0.25%, taking 5.99% to 5.74%. The payment drops from $2,058.10 to $2,003.22, a $54.88 monthly saving. Break-even: 62.6 months. Points are a long horizon bet, nothing more.

Three things that are not savings

• Your escrow refund. That is your money coming back. You will fund a new escrow account at closing.
• The "skipped" payment. Interest accrued for that month and got rolled into the payoff. Nothing was skipped.
• Cash out proceeds. That is new debt at a mortgage rate, which may still be a fine trade, but it is not a refinance saving and it does not belong in the break-even.

Ask every lender for a Loan Estimate, compare page 2 line by line, and run the total interest yourself over the same number of years. Fifteen minutes with a spreadsheet is worth more than any rate you can negotiate.