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
Higher-value path
Invest
Investing path value
$18,405
Extra payment path value
$14,940
Difference
$3,465
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How to use this
- 1Enter current loan balance ($).
- 2Enter loan interest rate (%).
- 3Enter extra monthly amount ($).
- 4Enter expected investment return (%).
- 5Enter time horizon.
- 6Read your higher-value path on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
This is the general-purpose version of the payoff-vs-invest question for any installment loan, not just a mortgage: student loans, auto loans, or personal loans. It compares the guaranteed return of eliminating interest at your loan's rate against putting the same extra dollars into an investment account at an expected market return, accounting for the fact that the loan path frees up cash sooner once paid off.
Worked example
Using the values the calculator loads with:
Inputs
- Current loan balance: 18000 $
- Loan interest rate: 7.5 %
- Extra monthly amount: 200 $
- Expected investment return: 8 %
- Time horizon: 6
Results
- Higher-value path: Invest
- Investing path value: $18,405
- Extra payment path value: $14,940
- Difference: $3,465
What each field means
Inputs
- Current loan balance ($)
- The current loan balance used in the calculation, measured in $. Starts at 18000 $ so you have a working example on load.
- Loan interest rate (%)
- The loan interest rate used in the calculation, measured in %. Starts at 7.5 % so you have a working example on load. Accepted range: 0–30 %.
- Extra monthly amount ($)
- The extra monthly amount used in the calculation, measured in $. Starts at 200 $ so you have a working example on load.
- Expected investment return (%)
- The expected investment return used in the calculation, measured in %. Starts at 8 % so you have a working example on load. Accepted range: 0–20 %.
- Time horizon
- The time horizon used in the calculation. Starts at 6 so you have a working example on load. Accepted range: 1–30.
Results
- Higher-value path
- Returned as a plain value and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Investing path value
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Extra payment path value
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Difference
- 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 is this different from the mortgage version?
Same math, applied to shorter, higher-rate debts like auto or student loans, where the guaranteed 'return' from extra payments is often higher than a mortgage rate, tipping the scale toward payoff more often.
Should I pay off high-rate debt before investing at all?
Generally yes for anything above 8-10% interest — few reliable investments beat that after taxes and risk, which is why credit card and high-rate personal loan payoff nearly always wins this comparison.
What if my employer matches 401k contributions?
Capture the full match first regardless of what this calculator says — it's an immediate guaranteed return that beats both paths here.
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). Extra Payment vs Invest Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/extra-principal-vs-invest
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/extra-principal-vs-invest" target="_blank" rel="noopener">Extra Payment vs Invest Calculator — RevenueLab</a> (2026).</p>
Source: [Extra Payment vs Invest Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/extra-principal-vs-invest) (2026).