Pay Off Debt or Invest? The 5% Rule

Pay off debt above 5–6% APR — invest when debt costs less

If your debt charges more than 5–6% interest, paying it off first almost always wins. Below that threshold, investing the extra cash typically produces a better outcome over time. The break-even point depends on your debt rate, expected investment return, tax implications, and risk tolerance — but the 5–6% guideline covers most situations.

The math: $500/month toward debt vs investments

Assume you have $20,000 in debt and $500/month in extra cash. Here is what happens over 5 years depending on where you direct that money:

Scenario A: Debt at 22% APR (credit card)

• Pay off debt: Eliminated in 62 months, saving $15,800 in interest
• Invest instead: $35,800 in portfolio, but still owe $20,000 plus $22,000 in accumulated interest
• Winner: Pay off debt (by a wide margin — guaranteed 22% return)

Scenario B: Debt at 7% APR (car loan or student loan)

• Pay off debt: Eliminated in 44 months, saving $3,200 in interest
• Invest at 7%: $35,800 in portfolio, remaining debt $5,400
• Net position investing: $30,400 vs paying off debt: $35,800 in portfolio starting after month 44
• Near break-even — slight edge to paying off debt due to guaranteed return

Scenario C: Debt at 3.5% APR (subsidised student loan or old mortgage)

• Pay off debt: Eliminated in 42 months, saving $1,400 in interest
• Invest at 7%: $35,800 in portfolio, remaining debt $3,800
• Net position investing: $32,000 vs paying off debt: starts investing only at month 42
• Winner: Invest (the 3.5% spread compounds significantly over time)

The hierarchy most financial advisers recommend

1. First: Minimum payments on all debts (avoiding defaults and penalties)
2. Second: Employer 401(k) match (50–100% guaranteed return — beats any debt payoff)
3. Third: Pay off debt above 7% (credit cards, personal loans, high-rate student loans)
4. Fourth: Max Roth IRA ($7,000/year of tax-free growth)
5. Fifth: Pay off debt between 4–7% (car loans, moderate student loans)
6. Sixth: Invest more (additional 401(k), taxable brokerage)
7. Last: Pay off debt below 4% (mortgages, subsidised federal loans)

Why debt payoff is not always optimal

Three factors make investing the better choice when debt rates are low:

1. Tax benefits of investing 401(k) contributions save you 22–37% in taxes depending on your bracket. A $500/month 401(k) contribution at 22% marginal rate saves $110/month in taxes. The after-tax cost is only $390 for $500 in retirement savings. Meanwhile, debt payments come from after-tax dollars with no deduction (except mortgage interest for some filers).

2. Compound growth over long periods $500/month invested at 7% for 30 years grows to $566,765. That same $500/month paying off a 4% loan saves $24,000 in interest over 5 years, then you invest $500/month for the remaining 25 years: $405,070. The early start to investing wins by $161,695.

3. Liquidity Money in an investment account is accessible (with some tax consequences). Money that went to debt payoff is gone — it reduced a liability but did not create an accessible asset. In an emergency, the investor has a portfolio to draw from.

Why debt payoff sometimes wins anyway

Guaranteed return. Paying off a 7% loan guarantees a 7% return. Investing at an expected 7% return means some years you earn 20% and other years you lose 15%. The guaranteed return has real value if you are risk-averse.

Behavioural benefit. Debt is stressful. Eliminating it improves sleep, mental health, and decision-making. The psychological return on being debt-free is worth something — even if the spreadsheet says investing is mathematically optimal.

Cash flow improvement. Once a $400/month car payment is gone, you have $400/month in permanent cash flow improvement. This creates flexibility regardless of market conditions.

The “avalanche of priorities” approach

If you have $500/month of extra cash and multiple competing priorities:

• $200 → 401(k) up to employer match (free money)
• $200 → highest-rate debt above 6%
• $100 → emergency fund until it reaches $5,000

Once the high-rate debt is gone, redirect that $200 to investing. Once the emergency fund is full, redirect that $100 too. Eventually all $500/month goes to investing.

Use the Debt Payoff Calculator to see how quickly you can eliminate your specific debts, then compare the timeline against investment growth.