Student Loan vs Invest Calculator

What this calculator does

An investor with a fixed amount of monthly cash flow available — say a recent raise, a side income, or freed-up rent — can deploy it toward an existing student loan or into an investment account. This calculator runs both paths against the same monthly figure over the same horizon and shows the projected difference. The output expresses how much more (or less) wealth the investing path produces in nominal terms relative to the interest-saved path.

How the comparison is set up

The investing side computes the future value of the extra monthly amount invested at the entered annual return, with monthly compounding, over the years remaining. The loan-repayment side runs two amortisation simulations on the loan: one using the standard monthly payment alone, and one using the standard payment plus the extra. The difference between the total interest paid under the two schedules is the interest saved by the accelerated payoff. The headline figure is the gap between the investment future value and the interest saved.

Worked example

Take a 50,000 loan balance at 6% annual rate over 20 years remaining, with 300 extra per month available, and an expected 7% annual investment return. The standard amortising payment on the loan is approximately 358.22 per month for 240 months, accruing about 35,972 in total interest. Adding 300 each month brings the payment to 658.22 and clears the loan in approximately 96 months — roughly 12 years earlier — accruing about 13,048 in total interest. Interest saved: about 22,924. Investing 300 per month at 7% over the same 20-year window produces a future value of about 156,278. The gap between the two paths is about 133,354 in favour of investing on these inputs.

What moves the result

Three factors shape the outcome. The student loan rate determines how much interest the accelerated payoff saves — higher rates produce larger savings and tilt the comparison toward loan repayment. The investment return determines the future value of the invested path — higher returns weighs toward investing. The years remaining amplifies compounding on both sides simultaneously, but the investment side typically benefits more because compounding runs untaxed inside sheltered accounts and over longer horizons. When loan rate and investment return are close, the comparison flattens; when they diverge by 2 percentage points or more, the gap widens quickly.

What this calculation does not capture

The simulation assumes both rates stay fixed for the entire horizon. Real student loan rates can be variable, and real investment returns are stochastic — the calculator's expected return is a long-run assumption, not a guarantee. The model also does not capture: tax treatment of investment returns (which can reduce the net investment outcome by 0.5 to 2 percentage points annually for taxable accounts), sequence-of-returns risk on the investment side, what the borrower does with the freed cash flow after the loan clears in the accelerated path, prepayment penalties on some loans, employer matching on retirement accounts, and the value of debt-free flexibility (no minimum payment obligation) versus the value of a larger investment balance.

How to read the verdict

The headline label says which path produces the higher projected nominal value at the end of the horizon. It does not say which path is the right one for the borrower's situation. A higher projected investment value comes with market risk; a higher interest-saved figure comes with the certainty of debt removal but a lower nominal terminal value. The calculator surfaces the math so the comparison can be made on equal terms; the actual choice depends on factors the calculator does not model.