Compare your current loan with a refinance. Enter the remaining balance and payment — or the original amount and time left — then a new term, rate, points, fees, and optional cash-out. The result is a side-by-side of payment, length, interest, APR, lifetime savings, and the month you break even on closing costs.
What the comparison shows
| Row | Current | New |
|---|---|---|
| Principal | Remaining balance | Remaining + cash-out |
| Monthly pay | Current payment | Amortized new payment |
| Length | Months left on the current loan | New term in months |
| Interest rate / APR | Note rate | APR including points and fees |
| Total payments / interest | Over the remaining current term | Over the new term |
| Upfront | $0 | Costs + points |
| Break-even | — | Months until interest savings cover U |
Examples
Remaining $250,000 at 7%, payment $1,800, refinance to 20 years at 6%
Two points and $1,500 of fees cost $6,500 upfront. The new payment is $1,791.08 (APR 6.329%), $8.92 less per month, 45 months faster, and $76,641.36 cheaper over the remaining life. Break-even is 30 months.
Original $300,000 30-year at 7%, 20 years left, $20,000 cash-out into 15 years at 5.5%
The remaining balance is about $257,437.15; the new principal is $277,437.15. Payments go from $1,995.91 to $2,266.89 over 240 → 180 months. Take-home after 2 points and $1,500 of fees is about $12,951.
Formula
Monthly compounding uses i = R / 1200. The level payment on principal P over N months is:
payment(P, i, N) = P × i / (1 − (1 + i)^(−N))
Remaining balance known (mode b). Remaining months
N = floor(−ln(1 − P×i/A) / ln(1+i)), total remaining payments T = A × N,
interest I = T − P.
Original amount known (mode t). Compute the original payment, then the
balance after k = Norig − Nrem payments. Remaining totals use
T = A × Nrem.
New loan. Pnew = Pcurrent + cashOut, Anew = payment(Pnew, i_new, Nnew),
upfront U = costs + (points/100) × Pnew. APR is the annual rate j that
satisfies:
Anew = (Pnew − U) × (j/12) / (1 − (1 + j/12)^(−Nnew))
Lifetime savings is current remaining interest minus new interest minus U. Break-even is the first month where cumulative interest savings cover U.
Decision limits and source documents
This comparison holds both interest rates constant and assumes every scheduled payment is made. It excludes taxes, insurance, escrow changes, tax consequences, prepayment penalties, and the investment value of cash paid upfront. “Lifetime savings” can look better simply because the new loan has a shorter term; review payment and term together.
Use the note rate, points, lender credits, and costs from actual disclosures. The calculator's interest-savings break-even is one planning measure and may differ from a cash-flow break-even based on the monthly payment change.