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
Investing advantage at the horizon
-$318
Net worth — payoff first
$150,243
Net worth — invest first
$149,926
Interest saved by paying off early
$8,352
Total interest — payoff path
$6,726
Total interest — invest path
$15,078
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
Got your number — what next?
Pick one, it takes 20 secondsHow to use this
- 1Enter loan balance ($).
- 2Enter loan interest rate (%).
- 3Enter scheduled monthly payment ($/mo).
- 4Enter spare cash per month ($/mo).
- 5Enter expected investment return (%).
- 6Enter tax drag on returns (%).
- 7Enter comparison horizon (years).
- 8Read your investing advantage at the horizon on the right — it updates as you type.
- 9Hit Share to keep the scenario or send it to someone.
About this calculator
With spare cash and a student loan, the choice is between a guaranteed return equal to the loan rate and an uncertain return from investing. This calculator projects both paths over your chosen horizon: extra payments shorten the loan and eliminate interest, while investing accumulates at your expected return net of tax. It reports the net worth difference at the end of the horizon. The honest framing is that the loan payoff is risk-free and the investment return is not, so a modest edge for investing is not a decisive edge — but a large gap, especially with an employer retirement match in play, usually is.
Worked example
Using the values the calculator loads with:
Inputs
- Loan balance: 42000 $
- Loan interest rate: 6.5 %
- Scheduled monthly payment: 480 $/mo
- Spare cash per month: 400 $/mo
- Expected investment return: 7 %
- Tax drag on returns: 15 %
- Comparison horizon: 15 years
Results
- Investing advantage at the horizon: -$317.71
- Net worth — payoff first: $150,243.22
- Net worth — invest first: $149,925.51
- Interest saved by paying off early: $8,352.39
- Total interest — payoff path: $6,726.04
- Total interest — invest path: $15,078.43
What each field means
Inputs
- Loan balance ($)
- The loan balance used in the calculation, measured in $. Starts at 42000 $ so you have a working example on load.
- Loan interest rate (%)
- The loan interest rate used in the calculation, measured in %. Starts at 6.5 % so you have a working example on load.
- Scheduled monthly payment ($/mo)
- The scheduled monthly payment used in the calculation, measured in $/mo. Starts at 480 $/mo so you have a working example on load.
- Spare cash per month ($/mo)
- The spare cash per month used in the calculation, measured in $/mo. Starts at 400 $/mo so you have a working example on load.
- Expected investment return (%)
- The expected investment return used in the calculation, measured in %. Starts at 7 % so you have a working example on load.
- Tax drag on returns (%)
- The tax drag on returns used in the calculation, measured in %. Starts at 15 % so you have a working example on load. Accepted range: 0–50 %.
- Comparison horizon (years)
- The comparison horizon used in the calculation, measured in years. Starts at 15 years so you have a working example on load.
Results
- Investing advantage at the horizon
- 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.
- Net worth — payoff first
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Net worth — invest first
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Interest saved by paying off early
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total interest — payoff path
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total interest — invest path
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
A negative advantage means what?
That paying the loan down first leaves you better off at the horizon under these assumptions — which happens whenever the loan rate exceeds your after-tax expected return. Since the payoff return is guaranteed and the investment return is not, a negative number is a strong signal.
Does an employer match change the answer?
Enormously. A dollar-for-dollar match is an immediate 100% return that no loan rate can beat, so contribute at least up to the match before considering extra loan payments. This calculator does not model the match — treat it as a separate, first-priority allocation.
What about federal loan forgiveness programmes?
If you are pursuing forgiveness on an income-driven plan, extra payments can be actively counterproductive because they reduce a balance that may be cancelled. This model assumes a standard repayment with no forgiveness.
How should I treat variable-rate loans?
Model the rate you expect on average over the horizon, then re-run with a higher rate to see the downside. Variable-rate debt shifts risk to you, which strengthens the case for paying it down rather than betting the spread.
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
Extra Mortgage Payment Impact Calculator
See the years and interest an extra monthly amount removes from a loan.
Debt Avalanche vs Snowball Calculator
See how much interest the highest-rate-first order saves against smallest-balance-first.
Savings Goal Date Calculator
Find the month you hit a savings target at your current contribution and rate.
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Student Loan Payoff vs Invest Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/student-loan-payoff-vs-invest
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/student-loan-payoff-vs-invest" target="_blank" rel="noopener">Student Loan Payoff vs Invest Calculator — RevenueLab</a> (2026).</p>
Source: [Student Loan Payoff vs Invest Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/student-loan-payoff-vs-invest) (2026).