Mortgage Refinance Calculator: Compare Costs & Savings

A lower mortgage payment can hide a more expensive refinance when closing costs are high or a new term pushes the payoff date farther out. Compare the payment change with the loan balances and costs at the point you expect to sell, refinance again or pay off the mortgage.

How to Use the Mortgage Refinance Calculator

Start with the unpaid principal balance, note interest rate and approximate years remaining on your current fixed-rate mortgage. Then enter the proposed refinance rate, new term, expected loan costs and the period you expect to keep the new mortgage.

Use the mortgage interest rate rather than APR in both rate fields. APR is a broader measure that can include points and other charges, while a fixed-rate amortization calculation uses the contractual interest rate to determine scheduled principal-and-interest payments.

Rate-and-term comparison is the focus here, so cash-out borrowing is excluded. Cash-out borrowing creates a different decision because the borrower receives new cash as part of the transaction; that scenario belongs in the cash-out refinance calculator.

A Lower Payment Is Not the Same as a Cheaper Refinance

Extending the payoff date can reduce the monthly bill even when the new mortgage costs more overall. For a homeowner with 20 years remaining, moving into a fresh 30-year term may create immediate payment relief while also carrying debt for another decade.

Monthly principal and interest therefore anchor the first result card. Taxes, homeowners insurance, HOA dues and mortgage insurance are not mixed into the payment comparison because they are not determined by the fixed-rate amortization formula and may change independently.

A separate horizon result answers a different question: what would each mortgage path cost at the end of the period you actually care about? Scheduled payments alone cannot answer that because two loans may leave very different principal balances after five or ten years.

Shortening the refinance term can produce the opposite pattern. With a shorter term, payments may rise while the balance falls much faster, making a higher payment compatible with lower financing cost over time. Homeowners considering extra payments instead of a new loan can model that alternative with the mortgage payoff calculator.

How the Horizon and Break-Even Calculations Work

Both options are evaluated at the same future date in the horizon comparison. At that point, the calculator adds the principal-and-interest payments already made to the remaining principal that would still need to be paid off.

Financed costs do not appear again as a separate subtraction because they are already part of the new principal, monthly payment and remaining balance. Counting the same amount again would overstate the cost of that scenario.

Month-by-month break-even testing uses the same framework. Break-even is the first month when the modeled refinance path is no more expensive than keeping the existing mortgage, assuming both loans were paid off at that comparison date.

This approach is broader than the familiar shortcut of dividing upfront costs by monthly payment savings. That shortcut is useful when the loan balances follow similar paths, but it can hide the effect of resetting the term or financing closing costs.

Closing Costs and the New Loan Structure Matter

Refinancing replaces the existing mortgage with a new loan, so transaction costs need to be included somewhere in the comparison. Paying them upfront creates an immediate cash outflow; adding them to the mortgage increases principal and causes those costs to accrue interest over the new term.

Offers described as “no-closing-cost” refinances can still carry a cost. One common structure uses a lender credit in exchange for a higher interest rate, while another adds eligible costs to the loan balance. Comparing only the cash needed on closing day can therefore miss the longer-term trade-off.

Once a lender provides a Loan Estimate, it becomes the better source for the scenario inputs. Page 1 of the Loan Estimate separates the interest rate from APR, while the form also shows estimated loan costs that can replace hypothetical inputs with offer-specific figures.

What the Calculator Cannot Decide

Several refinance factors depend on the borrower, property and loan program rather than the amortization formula. Approval, available rate, appraisal value, debt-to-income ratio, credit history and lender overlays all sit outside this planning model.

Mortgage insurance can also change the real payment comparison. Moving from a loan with mortgage insurance to one without it may create savings the calculator does not show, while a new requirement could move the result in the other direction.

Adjustable-rate mortgages require separate assumptions because future rates and payments are uncertain. Because the tool models fixed-rate current and replacement mortgages, an ARM-to-fixed refinance needs separate consideration of the current ARM terms and future-reset risk.

Prepayment penalties deserve a final check on the existing loan as well. Any penalty triggered by refinancing increases the real transaction cost and should be added to the refinance-cost input when applicable.