Mortgage Refinance Calculator

Introduction: why mortgage refinance comparisons matter

Refinancing a mortgage looks straightforward until you separate the lower rate from the upfront fee package, the remaining balance, and the number of years left on the old loan. This calculator keeps those pieces together so you can compare the current loan with a proposed refinance and see whether the savings are large enough to justify the switch.

The strongest refinance decisions are the ones you can explain in plain language: the new payment is lower, the break-even date is soon enough for your plans, and the long-run interest picture still makes sense. The notes on this page show how each input feeds the estimate so you can judge the result with your own loan terms instead of a generic rule of thumb.

The sections below walk through the refinance question, how to enter the loan details, how the payment and break-even math work, and which assumptions deserve a second look before you rely on the output.

What problem does this calculator solve?

Mortgage refinance decisions usually come down to a narrow question: does the new loan save enough each month to repay the closing costs, points, and any extra interest created by a longer term? This calculator turns that question into a side-by-side comparison of the current loan and the proposed refinance.

Before you start, define the refinance goal in one sentence. You might be trying to lower the payment, shorten the payoff timeline, recover fee costs quickly, or compare several lender quotes. Once the goal is clear, the fields on the form become a checklist rather than a guess.

How to use this mortgage refinance calculator

1. Enter Current Loan Balance ($) with the unit shown beside the field.
2. Enter Current Interest Rate (%) with the unit shown beside the field.
3. Enter Remaining Term (years) with the unit shown beside the field.
4. Enter New Interest Rate (%) with the unit shown beside the field.
5. Enter New Loan Term (years) with the unit shown beside the field.
6. Enter Start Date (optional) if you want the payoff and break-even dates anchored to a specific month.
7. Click Calculate to update the refinance payment, monthly savings, and break-even estimate.
8. Review whether the new payment, fee recovery time, and payoff dates fit the way you plan to keep the loan.

If you're comparing more than one lender quote, save the inputs you used for each run so you can tell which offer actually improves the numbers.

Mortgage refinance inputs: how to pick good values

For a mortgage refinance comparison, the cleanest inputs come from your current mortgage statement and the new lender's written quote.

The calculator’s form collects the variables that drive the result. Many refinance errors come from mixing up units or comparing quotes that do not use the same assumptions. Use the checklist below as you enter the numbers:

• Units: keep dollars in dollars, rates in percentages, and loan terms in years so the refinance math stays consistent.
• Ranges: if a quote looks outside the normal range for your market or budget, double-check it before you compare offers.
• Defaults: any shared example values are only placeholders; replace them with your own balance, rate, term, closing costs, and points before trusting the output.
• Consistency: if two refinance quotes use different assumptions, normalize them before comparing the results.

Common refinance inputs for this calculator include:

• Current Loan Balance ($): the unpaid principal left on the existing mortgage.
• Current Interest Rate (%): the note rate on the current loan.
• Remaining Term (years): the number of years left before the current mortgage would be paid off if you never refinanced.
• New Interest Rate (%): the quoted rate on the proposed refinance.
• New Loan Term (years): the length of the new loan in years.
• Start Date (optional): the month you want the refinance timeline to begin.
• Refinance Closing Costs ($): lender, title, and third-party fees you would pay to close the refinance.
• Discount Points (% of loan, optional): any upfront points charged as a percentage of the loan balance; in this calculator, points add to the upfront cost, so enter any lower rate separately if the lender's quote includes one.

If you're unsure about an estimate, use the lender's exact quote rather than a rounded figure. A slightly conservative rate or fee estimate is better than overpromising savings.

Mortgage refinance formulas: payment, savings, and break-even

This mortgage refinance calculator uses the standard fixed-rate amortization formula to estimate the monthly payment on the current loan and the proposed refinance.

Here, P is the loan balance, r is the monthly interest rate, and n is the number of monthly payments. When the rate is zero, the payment falls back to principal divided by the number of months.

The break-even calculation compares the refinance's upfront cost with the monthly savings from the lower payment.

Here, F is closing costs plus the points cost, and S is the difference between the current payment and the new payment. If monthly savings are zero or negative, the refinance does not pay for itself through payment reduction alone.

The results panel also compares cumulative interest across both amortization schedules and adds the refinance fees to the new-loan side, which is why a lower payment and a longer term can point in different directions.

Mortgage refinance worked example (step-by-step)

A refinance walkthrough is easiest to follow when you trace the old loan, the new loan, and the fees in order.

First, the calculator uses your current balance, current rate, and remaining term to estimate the payment on the loan you already have. Next, it applies the proposed refinance rate and term to the same balance to estimate the new monthly payment. The difference between those two figures is the monthly savings, if any.

After that, the calculator adds closing costs and any points to build the refinance's upfront cost. It then divides that amount by the monthly savings to estimate the break-even point. If the refinance saves money every month but the fee recovery period is longer than the time you expect to keep the mortgage, the better rate may still be the wrong practical choice.

In a real scenario, you would compare at least two offers: one that emphasizes a lower payment and one that emphasizes a shorter term. The right answer is the one that fits your timeline, not just the one that looks cheapest on the first monthly statement.

Refinance sensitivity: how rate, term, and fees change the answer

A mortgage refinance is usually most sensitive to the new rate, the amount of upfront fees, and the remaining term on the old loan. The table below shows the direction of that relationship without pretending that the moves can be reduced to a fake sum.

Use the refinance result to test a handful of realistic quotes rather than trying to chase the mathematically best rate in isolation. The best offer is the one whose payment and break-even both work for your actual plans.

How to interpret the mortgage refinance result

The mortgage refinance result is most useful when you read the payment, savings, and break-even together. A lower monthly payment is helpful, but it is only half the story if the fee recovery period is longer than you expect to keep the loan.

Look first at New Payment and Monthly Savings. If Monthly Savings is positive, the refinance reduces the payment load each month; if it is zero or negative, the lower rate is not enough to overcome the new terms. Then check Break-even, which tells you how many months it takes for the monthly savings to repay the upfront costs.

Current Payoff and New Payoff show how the timelines differ under each loan. Because this calculator advances the dates by whole months from the start date you enter, the payoff dates are best treated as planning dates rather than a day-by-day amortization forecast.

If the refinance improves cash flow, recovers fees before you expect to move or refinance again, and still leaves you comfortable with the new term length, the result is a strong candidate. If any one of those checks fails, use the calculator again with a different offer or a shorter term.

Limitations and assumptions for refinance estimates

Mortgage refinance estimates are most reliable when the loan is fixed-rate, fully amortizing, and the fee quote is complete.

• Input interpretation: read each field literally; balance, rates, term, closing costs, and points each feed a different part of the refinance math.
• Unit conversions: keep rate inputs as percentages, loan terms as years, and upfront costs as dollars so the payment and break-even math stays aligned.
• Rate and term stability: the formula assumes the quoted rate and loan term stay fixed for the life of the new loan.
• Scope: the estimate is limited to principal, interest, closing costs, and points; taxes, insurance, escrow changes, lender credits, and prepayment penalties are outside the calculation.
• Points handling: points are treated as an upfront cost in this calculator; if a lender's rate quote already reflects a buydown, enter the lower rate separately and use the points field for the cost.
• Rounding: displayed dollars are rounded for readability, so tiny differences between offers are normal.

If you use the output to compare refinance offers, make sure each quote is based on the same balance and closing-cost assumptions. The calculator is most helpful when it shows which part of the deal is doing the work and where the refinance stops making sense.