Blog · Money basics
Should you pay off debt or invest? The whole argument fits in one number: 6 percent. If your debt costs more than 6 percent, paying it off almost always beats investing. If it costs less, investing usually wins. Everything else in this debate is commentary on that line, and I am going to show you the math both ways so you never have to take it on faith.
Financial planners use 6 percent as the sorting line, and it is grounded in market history. A diversified portfolio of US stocks has returned roughly 10 percent a year over long periods, or about 6 to 7 percent after inflation. Planners commonly use 6 percent as the conservative long-term baseline when they model projections. So the comparison is simple: your debt's interest rate against 6 percent. Paying off debt is a guaranteed return equal to its interest rate. Investing is an expected return that is never guaranteed in any given year. Guaranteed beats expected at the same rate, which is why the line sits at 6 rather than 10.
Take $5,000 in extra cash and a credit card charging 10 percent. Pay off the debt and you save $500 in interest this year, guaranteed. Invest it at an expected 7 percent and you earn roughly $350, not guaranteed. The debt wins by $150, every time, and the return is locked in because you are eliminating a real cost, not betting on a future gain.
Now flip it. Same $5,000, but the debt is a federal student loan at 3.5 percent. Paying it off early saves you $175 this year. Investing at 7 percent earns roughly $350, double the savings, and the tax advantages of a Roth IRA or 401(k) widen the gap further. The investment wins. Same dollars, opposite answer, one variable changed: the interest rate.
For the extreme version, look at the average credit card, which the Federal Reserve puts around 21.5 percent on accounts assessed interest. Ten thousand dollars of untouched 21 percent debt compounds to about $67,000 in a decade, while the same $10,000 invested at 10 percent grows to roughly $26,000. Running both at once leaves you about $41,000 poorer. No mainstream investment reliably outpaces 21 percent. High-interest debt is always the priority.
The practical version of the 6 percent rule has three zones. Above 8 percent: pay the debt down first, always. This is most credit cards and many personal loans. Below 5 percent: lean toward investing while making minimum payments. This is low fixed-rate mortgages and subsidized student loans. Between 5 and 8 percent: use the 6 percent line as the tiebreaker, and a hybrid split is reasonable on either side. Revisit every six months as the balance drops.
One rule beats all three zones: capture any employer 401(k) match first. A typical match is a 50 to 100 percent instant return on your contribution, which beats every debt rate ever quoted. The match comes before the debt payoff, before the taxable investing, before everything.
Here is where I will be honest about the limit of my own answer. Carrying debt causes real stress, and for some people the mental reward of being completely debt-free outweighs what the numbers say. Paying off a 4 percent car loan early is mathematically inferior to investing, and plenty of disciplined people do it anyway because they sleep better with no car payment. I cannot argue them out of it, and I am not sure I should try.
The reverse is also true. Some people use the math as permission to carry debt they could clear, and the debt shapes their behavior: bigger purchases, thinner emergency funds, a baseline of anxiety they stop noticing. Being right on the spreadsheet is not the same as being right for your life. Run the 6 percent rule, do what it says, and then check whether the answer feels right. If it does not, figure out why before you act. Sometimes the reason is fear, and sometimes it is wisdom, and they feel identical until you interrogate them.
Above roughly 8% interest, paying off debt first is almost always right: no mainstream investment reliably beats that cost. Below about 5%, long-term market returns have historically won. Between 5% and 8%, the 6% rule breaks the tie.
An employer 401(k) match is an instant 50 to 100% return on your contribution, which beats every debt rate. Capture the full match before deciding between extra debt payments and investing.
For close calls, split your extra cash between both: half to the debt, half to investments. Revisit every six months as the balance drops and the rate situation changes.
Carrying debt causes real stress, and for some people the mental reward of being debt-free outweighs the mathematical edge of investing. Eliminating debt also frees up monthly cash flow. The math is the starting point, not the whole answer.
One practical money guide a week. Real numbers, no fluff.