Pay Off Student Loans or Invest? Your Repayment Plan Changes the Math

Paying off a student loan earns you its interest rate, guaranteed, and investing earns whatever the market returns, which is not. That is the whole comparison for a private loan. For a federal loan on the right repayment plan, three things can change it: a balance headed for forgiveness, a payment calculated from your income, and an employer that matches loan payments.

• The usual math compares a certain rate to an uncertain return. It holds when your loan will be repaid in full.

• On a forgiveness track, a prepaid dollar can earn almost nothing. It reduces a balance that was going to be cancelled.

• A pre-tax retirement contribution can lower an income-driven loan payment. On one plan, by more than you would expect.

• Some employers now match student loan payments into a retirement account. It is uncommon, and worth checking.

Paying down a loan returns its interest rate with certainty, and investing returns an amount no one can know in advance.

The loan side is guaranteed. Every dollar of principal you retire stops accruing interest at the loan’s rate. Undergraduate Direct Loans issued for the 2026-27 year carry a fixed 6.52%, and loans from 2025-26 carry 6.39%. Paying one down early returns exactly that rate, with no chance of doing worse.

The investment side is not. Markets have produced higher long-run averages than those rates, but an average is not a promise, and any given stretch of years can come in lower or negative. The comparison is between a certain number and an expected one, and how much weight to give that difference is a personal judgment about risk.

The interest deduction narrows the loan side for some borrowers. Up to $2,500 of student loan interest a year can be deducted, subject to income limits, which lowers the loan’s effective rate for someone who qualifies. The income limits change each year.

For a private loan, this is the complete picture. Private loans have no forgiveness track and no income-driven plans, so nothing else changes the arithmetic.

An employer match is money added to your account the moment you contribute, before any market return at all.

If your employer matches retirement contributions up to a limit, the matched portion is a return on your own contribution that arrives immediately, regardless of what the account earns afterward. A contribution below the match threshold leaves that portion unclaimed. It is a different kind of number from both the loan rate and an expected market return, because it depends on neither.

If your federal loan balance is going to be forgiven, paying it down early reduces an amount that would have been cancelled, so the loan’s interest rate is the wrong number to compare against.

Your income-driven payment does not fall when your balance does. On an income-driven plan the monthly payment is calculated from your income and family size, not from what you owe. Extra principal leaves the bill unchanged.

What you actually pay is your monthly payment multiplied by the number of months. The remaining balance is cancelled at the end, whatever it is. A smaller balance is a smaller cancellation, not a smaller cost to you.

So on that track, the effective return on prepaying is close to zero. Against that, almost any use of the money compares favorably.

This only holds if you reach the end of the clock. The Department of Education’s own projections show that most borrowers who start with small balances repay in full before forgiveness arrives, because their payments retire the debt first. Whether you are likely to reach it is covered in should you pay off student loans early.

What the money is for depends on which forgiveness track you are on, because only one of them produces a tax bill.

On public service loan forgiveness, the money’s job is to stay available. Public service forgiveness is not federally taxable, so there is no bill to fund at the end. What money set aside can do is cover the two ways the plan can change course. Your income may rise, and your income-driven payment rises with it. Or you may decide not to finish the forgiveness path and want to pay the loans off instead. Money kept somewhere liquid and earning a return covers both. Money prepaid into the loan covers neither, and money locked into long-term investments may not be reachable when a payment jumps.

On income-driven forgiveness, the cancellation is taxable. Since January 1, 2026, a balance cancelled under an income-driven plan, including income-based repayment and the Repayment Assistance Plan, is ordinary income in the year it is discharged. Setting money aside toward that bill over the years before it arrives is one use of money that would otherwise have been prepaid.

There is an insolvency exception. If your liabilities exceed your assets immediately before the cancellation, you can exclude the cancelled amount from income up to the amount you were insolvent. The calculation counts most of what you own, including property creditors could not reach and accessible retirement accounts such as a 401(k) or IRA. Whether a traditional pension counts is disputed: the Tax Court has excluded a pension that could not be drawn on to pay the tax, and the IRS has said it disagrees. Planning around any of this is individual, and we are not tax advisors; a tax professional is the right person to run it.

Income-driven payments are calculated from your adjusted gross income, so a contribution that lowers that number can lower your loan payment at the same time it builds savings.

Traditional contributions reduce adjusted gross income; Roth contributions do not. A traditional 401(k), 403(b) or 457(b) contribution comes off your income before the payment formula sees it, and so, in some cases, does a traditional IRA contribution. The 2026 employee contribution limit for a 401(k) is $24,500. The full set of ways to lower that number is covered in how adjusted gross income affects your student loan payment.

The size of the effect depends on your plan. On income-based repayment, the payment is a percentage of your income above a buffer tied to the poverty guideline, so each dollar of contribution lowers the payment by a fixed fraction of a dollar.

The Repayment Assistance Plan works differently, and it can produce a larger drop. That plan charges a percentage of your whole adjusted gross income, and the percentage steps up at every $10,000 of income. Each band’s upper boundary belongs to the lower rate. Crossing a boundary downward lowers the percentage and the income it applies to at the same time.

A worked example. A single borrower with adjusted gross income of $99,740 falls in the 9% band and pays about $748 a month. A $9,740 traditional 401(k) contribution brings income to exactly $90,000, which is the 8% band. The payment becomes $600 a month, about $148 lower. If the rate had not changed, the same contribution would have lowered the payment by about $73; the rest comes from crossing the boundary. Reaching the same $600 payment on the older version of income-based repayment would take a contribution of roughly $27,590, which is above the annual limit.

The trade on this plan is time. The Repayment Assistance Plan runs 30 years to forgiveness, longer than income-based repayment’s 20 or 25. Payments made under income-based repayment count toward the new plan’s clock, but months under the Repayment Assistance Plan generally do not count back toward income-based repayment. Filing status and household size change every figure above. How the two plans compare in full is covered in income-based repayment versus the Repayment Assistance Plan.

Since 2024, federal law has allowed employers to make retirement matching contributions based on an employee’s student loan payments, as though the loan payments were contributions to the plan.

Where an employer offers it, a student loan payment can earn the same match that would otherwise have required a retirement contribution, which removes part of the choice between the two. It applies to 401(k), 403(b), governmental 457(b) and SIMPLE IRA plans, and the employee certifies the loan payments each year.

Employers are not required to offer it, and few do. Whether your plan includes it is a question for your benefits administrator.

Whether a forgiveness clock is running on your loans, and whether your payment responds to your income, decides which comparison you are actually making.

Your loan type. A private loan has no forgiveness track and no income-driven plan, so the standard rate-versus-return comparison is the whole answer.

Your repayment plan. On a standard, graduated or extended plan, no forgiveness clock is running and your payment does not respond to your income, so the standard comparison applies. On an income-driven plan, both the forgiveness question and the payment lever come into play.

How likely you are to reach forgiveness. A balance that is large relative to your income is more likely to outlast the clock. A small one is more likely to be repaid first, in which case the standard comparison applies after all.

Your employer. Qualifying public service employment puts you on the tax-free track, where keeping money available answers a different question from investing it. And your benefits package determines whether a retirement match, or a match on loan payments, is part of the math.

The student loan payoff guide covers the other decisions in the same family.