Refinancing into a longer term: check lifetime interest, not just the payment

A refinance pitch is almost always framed around one number: the new, lower monthly payment. That number is real, but it's only half the picture. Stretching a loan's remaining term back out — even at a genuinely better rate — can raise the total interest paid over the life of the loan at the same time it lowers the payment. Both things can be true about the same refinance, and only one of them shows up in the sales pitch.

The method

Compute four numbers, not one. First, the new payment at the new rate and new term. Second, the monthly saving: current payment minus new payment. Third, the interest still owed on the current loan if you kept paying it for its remaining months. Fourth, the interest the new loan charges over its own full term. Comparing the third and fourth numbers — not the payments — is what shows whether the refinance actually costs less over time.

A worked example

Balance: $220,000. Current loan: 6.75%, 300 months (25 years) remaining. New loan on offer: 5.50%, a fresh 30-year term (360 months). Closing cost: $4,000.

1. Current payment at 6.75% over 300 months: $1,520.01.
2. New payment at 5.50% over 360 months: $1,249.14.
3. Monthly saving: $1,520.01 − $1,249.14 = $270.87.
4. Break-even on the $4,000 closing cost: $4,000 ÷ $270.87 = 14.77, rounded up — 15 months to recover the cost.
5. Interest still owed on the current loan if paid out over its remaining 300 months: $236,001.61.
6. Interest the new loan charges over that same 300-month window: $220,136.54 — already less than the current loan's remaining interest, even before the new loan is paid off.
7. Interest the new loan charges over its own full 360-month term: $229,688.89.

In this case all three interest comparisons favor the refinance: even carried to its full new term, the new loan's total interest ($229,688.89) is still less than what remained to be paid on the old one ($236,001.61). But change the numbers slightly — a smaller rate gap, or a current loan with fewer months left — and the full-term interest figure can climb above the old loan's remaining interest even while the payment drops, because thirty fresh years of amortization outweighs a percentage point or two of rate. The payment saving is real either way; whether the loan is cheaper over its full life is a separate question, and this is the number that answers it.

What this doesn't include

This is payment and interest arithmetic on the numbers entered, run entirely on your own device with no network connection. It doesn't watch rates, doesn't recommend contacting anyone, and doesn't see credit, income, appraised value, escrow, mortgage insurance, or a prepayment penalty on the existing note. The figures above are an invented example, not market data or an offer — every input should come from your own statement and quote.

Run your own numbers

The free Refinance Screener tool takes a whole book of loans — balance, current rate, months left, and a closing cost — against one rate you quote, and shows the payment, the monthly saving, the break-even month, and both the remaining-term and full-new-term interest for every line, flagging any refinance that raises lifetime interest in capitals.