Should I Pay Off My Student Loans or Start Investing? (The Math Might Surprise You)

You finished residency, maybe fellowship too. You're finally earning real money — the average physician salary in 2025 was $386,000, according to Medscape — and you're staring at two numbers that feel like they're in direct competition: $223,000 in student loan debt (the AAMC Class of 2025 average) and a retirement account that's barely above zero.

Every dollar you put toward loans is a dollar that isn't compounding in your 401(k). Every dollar you invest is a dollar still accruing interest on a loan balance that feels like it'll never die. The internet is full of people who will confidently tell you which one to prioritize. Most of them are oversimplifying a decision that has at least six variables.

This post walks through the actual math, the tax wrinkles that change the answer for high earners, the PSLF question, and the behavioral factors that no calculator captures. By the end, you won't have a single "right" answer — but you'll have the framework to find yours.

The Simple Math (That Everyone Quotes)

The basic framework is straightforward: compare the interest rate on your loans to the expected return on your investments. If your expected return is higher, investing wins. If your loan rate is higher, paying off debt wins.

The S&P 500 has returned approximately 10% annually over the long term (nominal, before inflation). Your federal student loans, if you took out Direct Unsubsidized loans for med school between 2020 and 2025, carry interest rates between 5% and 8%. PLUS loans are 7% to 9%. For loans disbursed July 2025 through June 2026, the rates are 7.94% (Direct Unsubsidized) and 8.94% (Direct PLUS).

At first glance, 10% beats 7-9%. Invest everything, right?

Not so fast. That comparison ignores three critical adjustments.

The Three Adjustments Nobody Makes

1. The student loan interest deduction doesn't exist for you.

The federal student loan interest deduction allows you to deduct up to $2,500 in interest per year, which effectively lowers your loan's cost. But the deduction phases out completely at $90,000 of modified AGI for single filers and $185,000 for married filing jointly.

If you're an attending physician earning $300,000+, you get zero benefit from this deduction. Your effective interest rate is your stated interest rate — no discount. Meanwhile, online calculators that bake in the deduction may understate your true borrowing cost by up to a full percentage point.

2. Investment returns are pre-tax. Loan payoff is a guaranteed after-tax return.

The S&P 500's 10% average return is nominal and pre-tax. In a taxable brokerage account, you'll owe capital gains taxes on the growth, reducing the effective return to roughly 7-8% depending on your bracket, holding period, and state. In California, where capital gains are taxed as ordinary income at up to 13.3%, the drag is significant.

Paying off a loan at 7.5% interest is a guaranteed, risk-free, after-tax return of 7.5%. No market risk. No sequence-of-returns risk. No tax drag. To match that return in a taxable account, you'd need a pre-tax return of roughly 10-11%.

However — and this is where the math actually gets interesting — tax-advantaged accounts change the comparison entirely.

3. Tax-advantaged accounts create a return the loan can't match.

A dollar contributed to a pre-tax 401(k) or 403(b) at a 43% combined marginal rate (32% federal + 11% California) effectively costs you only $0.57 out of pocket. You get a $0.43 tax savings immediately — that's an instant 75% return on the money you actually part with, before the investments earn a single penny. Over decades, the tax-deferred compounding adds another 0.5% to 2% in effective annual return, depending on your withdrawal tax rate.

This is the argument that physician-finance experts like those at White Coat Investor have been making for years: the tax arbitrage on a 401(k) contribution for a high-income physician is so large that it almost always beats paying down even a high-interest loan.

The Decision Framework

Your effective after-tax interest rate — the rate after accounting for any deductions you actually qualify for (which for most attending physicians is zero) — determines which zone you're in:

Important: in all three zones, max your tax-advantaged accounts first. The decision framework above applies to what you do with money after you've captured the employer match, maxed the 401(k)/403(b), funded the backdoor Roth, and contributed to your HSA. For the full account ordering, see our post on the ideal investment order for high earners.

What About PSLF?

If you work for a qualifying nonprofit or government employer — which includes most academic medical centers, VA hospitals, and many health systems — Public Service Loan Forgiveness remains available. PSLF provides tax-free forgiveness of your remaining federal loan balance after 120 qualifying payments (10 years) on an income-driven repayment plan.

If you're pursuing PSLF, the calculus inverts completely. Every extra dollar you pay toward your loans is a dollar you could have invested, because the remaining balance will be forgiven anyway. The optimal strategy is to minimize payments (stay on the lowest IDR plan you qualify for) and invest the difference aggressively.

The Numbers, Spelled Out

Let's run the math on a specific scenario, because abstractions don't change behavior — concrete numbers do.

These are simplified illustrations assuming a constant 7% net return and ignoring the tax advantage of retirement accounts, which would further favor the investing strategies. In reality, the first dollars invested should go into a 401(k)/403(b) where the tax benefit adds an immediate ~43% boost.

The gap between Strategy A (all-in on debt) and Strategy B (all-in on investing) is roughly $250,000 over 20 years. That's real money — but it assumes a consistent 7% return and no major market drawdowns. Strategy C, the hybrid, lands in between and gives you the psychological benefit of watching the loan balance shrink while still getting money into the market early.

The Part The Math Misses

If this were purely a spreadsheet exercise, the answer would almost always be "invest more, pay loans slowly." But physicians don't live in spreadsheets.

The Order That Actually Works

Given all of these variables — the tax math, the rate comparison, the behavioral factors, and the 2026 regulatory landscape — here's the framework that works for most new attending physicians who are not pursuing PSLF:

For a deeper look at how all of these levers interact — especially the tax strategies available to high earners and the physician-specific tax playbook — we've written extensively on both.

The Bottom Line

The question "should I pay off loans or invest?" is actually three questions stacked on top of each other: where is the next dollar going (tax-advantaged account or not)? What's my effective after-tax interest rate on the loans? And how do I actually behave with money under stress?

For most physicians earning $300,000+, the answer is: max every tax-advantaged account first (that's always the right answer, regardless of loan balance), then use the rate-zone framework to decide what happens with the surplus. If your loans are above 7% and you're not pursuing PSLF, aggressive payoff of any remaining surplus after tax-advantaged accounts are maxed is defensible and often optimal. If you can refinance below 5%, investing the surplus has a strong historical edge.

The one answer that is never right: doing nothing while you figure it out. Every month of inaction costs you either compounding returns or accruing interest — and usually both.