Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Result
Interest saved
$99,772
Time saved
93
New payoff time
232
New monthly payment
$2,123.09
Interest if unchanged
$305,682
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter current balance ($).
- 2Enter interest rate (%).
- 3Enter years remaining.
- 4Enter extra monthly principal ($).
- 5Read your interest saved on the right — it updates as you type.
- 6Hit Share to keep the scenario or send it to someone.
About this calculator
Extra principal payments hit the back end of an amortisation schedule, where almost all of the remaining interest lives. Even a small monthly addition can cut years off a 30-year loan.
Worked example
Using the values the calculator loads with:
Inputs
- Current balance: 285000 $
- Interest rate: 6.25 %
- Years remaining: 27
- Extra monthly principal: 300 $
Results
- Interest saved: $99,772.40
- Time saved: 93
- New payoff time: 232
- New monthly payment: $2,123.09
- Interest if unchanged: $305,682.30
What each field means
Inputs
- Current balance ($)
- The current balance used in the calculation, measured in $. Starts at 285000 $ so you have a working example on load.
- Interest rate (%)
- The interest rate used in the calculation, measured in %. Starts at 6.25 % so you have a working example on load.
- Years remaining
- The years remaining used in the calculation. Starts at 27 so you have a working example on load.
- Extra monthly principal ($)
- The extra monthly principal used in the calculation, measured in $. Starts at 300 $ so you have a working example on load.
Results
- Interest saved
- Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Time saved
- Returned as a length of time. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- New payoff time
- Returned as a length of time. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- New monthly payment
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Interest if unchanged
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the mortgage payoff calculator work?
Extra principal payments hit the back end of an amortisation schedule, where almost all of the remaining interest lives. Even a small monthly addition can cut years off a 30-year loan. The underlying maths is: Compares the scheduled amortisation against the same loan with extra principal applied monthly.
What do I need to enter?
4 values: current balance, interest rate, years remaining, and extra monthly principal. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the interest saved result mean?
It is returned as a money amount in US dollars and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
Who is this tool for?
It's built for anyone comparing money scenarios before committing — budgeting a payment, sanity-checking a quote, or seeing what a change in rate or term actually costs.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Mortgage Payoff Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/mortgage-payoff
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/mortgage-payoff" target="_blank" rel="noopener">Mortgage Payoff Calculator — RevenueLab</a> (2026).</p>
Source: [Mortgage Payoff Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/mortgage-payoff) (2026).