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
Months to payoff
44
Total interest
$5,369
Total paid
$17,369
Status
On track
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter balance ($).
- 2Enter apr (%).
- 3Enter monthly payment ($).
- 4Read your months to payoff on the right — it updates as you type.
- 5Hit Share to keep the scenario or send it to someone.
About this calculator
Enter a balance, rate, and what you can pay each month. If the payment barely covers interest the tool will tell you — that is the trap that keeps balances alive for a decade.
Worked example
Using the values the calculator loads with:
Inputs
- Balance: 12000 $
- APR: 21.5 %
- Monthly payment: 400 $
Results
- Months to payoff: 44
- Total interest: $5,369.22
- Total paid: $17,369.22
- Status: On track
What each field means
Inputs
- Balance ($)
- The balance used in the calculation, measured in $. Starts at 12000 $ so you have a working example on load.
- APR (%)
- The apr used in the calculation, measured in %. Starts at 21.5 % so you have a working example on load.
- Monthly payment ($)
- The monthly payment used in the calculation, measured in $. Starts at 400 $ so you have a working example on load.
Results
- Months to payoff
- Returned as a length of time and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total interest
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total paid
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Status
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the debt payoff calculator work?
Enter a balance, rate, and what you can pay each month. If the payment barely covers interest the tool will tell you — that is the trap that keeps balances alive for a decade. The underlying maths is: Months = ln(Payment ÷ (Payment − Balance × r)) ÷ ln(1 + r), where r is the monthly rate.
What do I need to enter?
3 values: balance, apr, and monthly payment. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the months to payoff result mean?
It is returned as a length of time 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). Debt Payoff Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/debt-payoff
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/debt-payoff" target="_blank" rel="noopener">Debt Payoff Calculator — RevenueLab</a> (2026).</p>
Source: [Debt Payoff Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/debt-payoff) (2026).