Pay Off Debt vs Invest: Which Should You Do First?

The simple math

The decision comes down to one comparison: your debt’s interest rate versus your expected investment return after tax.

Credit card at 22% APR? Pay it off. No legal investment reliably returns 22% per year. That debt is costing you more than any portfolio could earn.

Mortgage at 3.5%? Invest. The stock market’s historical average return of 7-10% per year comfortably beats that rate. Your money works harder in a brokerage account than it does paying down cheap debt.

The grey zone sits between 5% and 7%. Car loans, some student loans, and personal loans often land here. At these rates, the mathematical edge of investing is slim, and the guaranteed return of paying off debt becomes more attractive.

The break-even calculation

Take your debt interest rate and compare it to your expected after-tax investment return. If you’re in the 22% US federal tax bracket investing in a taxable account with 8% expected returns, your after-tax return drops to roughly 6.2%.

That means any debt above 6.2% should be paid first — not just credit cards. A 7% car loan beats the risk-adjusted return of taxable investing.

Run both scenarios through a debt payoff calculator and an investment return calculator to see the exact numbers for your situation. The dollar difference over 5-10 years often surprises people.

The exception that changes everything: employer match

If your employer matches 401(k) contributions, contribute at least enough to get the full match before paying extra on any debt — even high-interest debt.

An employer matching 50% of contributions up to 6% of salary gives you an instant 50% return on that money. No credit card charges 50% APR. The match is the single highest guaranteed return available to most workers.

The order for most people with debt:

1. Contribute to 401(k)/pension up to the employer match
2. Build a small emergency buffer ($1,000-$2,000)
3. Attack high-interest debt (above 7%) aggressively
4. Once high-interest debt is gone, split extra money between medium-rate debt and investing

In the UK, workplace pension auto-enrolment works the same way. Your employer contributes 3% minimum on top of your 5%. Don’t opt out to pay debt — you’re turning down a pay rise.

The psychological factor

Math says invest if your debt rate is 5% and markets average 8%. But people aren’t spreadsheets.

Carrying debt causes measurable stress. A 2023 study by the American Psychological Association found that money is the top source of stress for US adults, and debt is the primary driver. Paying off a loan — even a low-rate one — removes a monthly obligation and mental burden.

If debt keeps you up at night, the mathematical advantage of investing a few extra percentage points doesn’t compensate for the anxiety. Peace of mind has real value, even if it doesn’t compound.

What about tax-advantaged accounts beyond the match?

After capturing the employer match and clearing high-interest debt, you face another choice: max out tax-advantaged accounts (401(k), IRA, ISA, SIPP) or keep attacking medium-rate debt?

Tax-advantaged accounts have annual contribution limits that don’t roll over. Miss a year of ISA allowance (£20,000) or 401(k) contributions ($23,500 in 2025), and that tax-free space is gone permanently.

For debt below 5%, prioritising these accounts usually wins. The tax savings alone — 20-40% immediate return on pension contributions, or decades of tax-free growth in an ISA — tip the balance firmly toward investing.

The decision framework

Pay debt first when:

• Interest rate is above 7%
• You have variable-rate debt that could increase
• Debt causes significant stress or limits major life decisions
• You’re not disciplined enough to invest consistently while carrying debt

Invest first when:

• Debt rate is below 5%
• You have an employer match you’re not capturing
• Tax-advantaged account limits would be wasted
• The debt is fixed-rate with decades of remaining term (like a low-rate mortgage)

Split the difference when:

• Debt rate is 5-7%
• You have both high-rate and low-rate debts (attack the expensive ones, invest alongside the cheap ones)