#How the break-even point is actually calculated
Most refinance calculators do something crude: divide your closing costs by your monthly payment saving and call the answer a break-even point. That works only if the new loan has the same remaining term as the old one, which is almost never true.
This calculator builds two complete amortisation schedules and compares them month by month. For every month it tracks three things: the cash you save or spend on payments, the difference in outstanding balance between the two loans, and the upfront cost you paid at closing. Break-even is the first month where your net position turns positive.
That last component matters enormously. If you refinance a 27-year remaining balance into a 15-year loan, your monthly payment goes up, so a payment-difference calculator will tell you the refinance never breaks even. In reality you are building equity far faster and paying dramatically less interest. By crediting the balance difference, this tool gives you the honest answer instead of the convenient one.
#The formula behind it
The monthly payment on a fully amortising loan is:
P = L × [ r(1+r)^n ] / [ (1+r)^n − 1 ]Where L is the loan amount, r is the monthly interest rate (annual rate ÷ 12) and n is the number of payments. The remaining balance after k payments is:
B(k) = L(1+r)^k − P × [ ((1+r)^k − 1) / r ]Everything else — total interest, the crossover point, the position at your expected sale date — falls out of running those two expressions across both loans.
#Reading the result correctly
The break-even month is a threshold, not a target. If it lands at 22 months and you are confident you will stay five years, the decision is easy. If it lands at 54 months and you are unsure, treat that as a no. The average US homeowner sells or refinances again within about seven years, and people consistently overestimate how long they will stay put.
Watch lifetime interest, not the monthly payment. Cutting your payment by $280 feels excellent. If you achieved it by restarting a 30-year clock on a loan you have already paid down for eight years, you may have added $60,000 to your lifetime interest. The comparison table shows both figures side by side precisely so this cannot hide.
Closing costs are the number lenders blur. Use the total from your official Loan Estimate, not a rate-sheet advertisement. Points, lender credits, title insurance, appraisal and prepaid escrow all move the figure materially, and a "no-cost" refinance simply prices those costs into a higher rate.
#Cases where refinancing wins even with a long break-even
- Removing PMI. If your equity has passed 20% and refinancing removes private mortgage insurance, enter your current PMI figure. That saving is often $150 to $300 a month and does not depend on the rate difference at all.
- Escaping an adjustable rate. Locking a fixed rate before an ARM resets is a risk decision, not purely an arithmetic one. The calculator will tell you the cost of that insurance.
- Shortening the term. Moving from 30 years to 15 usually raises the payment and slashes total interest. The net-position line is the honest scorecard here.
#Common mistakes this tool prevents
- Comparing payments instead of total cost. A lower payment on a longer term is usually more expensive.
- Ignoring how long you have already paid. Eleven years into a 30-year loan, a large share of each payment is finally going to principal. Restarting throws that progress away.
- Forgetting that rolled-in costs accrue interest. Financing $6,400 of closing costs at 5.75% over 30 years costs roughly $13,500 in total. Toggle the option to see it.
- Treating an advertised rate as your rate. Your actual rate depends on credit score, loan-to-value, occupancy, property type and points purchased.
#Who this is for
Homeowners with an existing mortgage evaluating a specific written offer, borrowers deciding between a rate-and-term and a cash-out refinance, and anyone trying to work out whether the mailer from their lender is worth opening. If you are still deciding whether to buy at all, start with the rent vs buy calculator instead.