Both are good uses of money, so you are choosing between two right answers. That is why the question is hard, and why people argue about it at dinner.
Here is the cleanest way to think about it.
The comparison
Every extra dollar you put on the mortgage earns you the mortgage’s interest rate. A 6.5% mortgage means a 6.5% return. No fees, no bad years, no uncertainty.
Every extra dollar you invest earns whatever the market gives. Over long stretches, stocks have earned more than most mortgage rates. But not every year. Since 1928, the S&P 500 has finished the year down 26 times out of 98.
So you are comparing a certain return with an uncertain one that is higher on average. Three checks decide which wins for you.
Check 1: Your rate
A low rate, say under 4%. The guaranteed return from paying it off is small. Over a long time, investing has usually done better. Paying extra is mostly a choice for peace of mind.
A high rate, say 7% or more. A guaranteed 7% is hard to beat once you account for the bad years. Paying extra is a strong choice.
In between. It is close to a tie on the numbers, which means the other two checks should decide it.
Check 2: Your cushion
Money sent to the mortgage is hard to get back. You cannot ask the bank to return last year’s extra payments when the roof leaks or the job ends.
So before either choice: a real emergency fund in cash. Then any employer match in your 401(k), because a match is an instant return nothing else can equal. Then any debt that costs more than the mortgage, such as credit cards.
Only then does the mortgage or invest question begin.
Check 3: Your sleep
Some people feel real weight from owing money on their home, and real freedom when it is gone. A paid-off house also lowers what you need each month, which makes every other risk in your life easier to carry: a job loss, a slow business year, a bad market early in retirement.
That is worth something, even though no spreadsheet shows it. If a paid-off home would change how you feel every morning, that counts.
The reverse is also true. If you would regret missing years of market growth, that counts too.
One choice is math. The other is sleep. Both are allowed.
The middle path
You do not have to choose once and forever. Many people split the extra money: half to the mortgage, half to investing. You will be half wrong either way, and half right either way, and you will not lose sleep over which.
If retirement is close, the weight shifts toward paying it off. Entering retirement without a mortgage payment means you need to withdraw less each year, and that protects your savings in a bad market.
One caution
Do not pull money out of a retirement account to pay off the house without running the tax first. A large withdrawal can push you into a higher bracket, and you could hand a big share of it to the IRS to save a much smaller amount of interest.
Run your own numbers
Related questions: the cost of too much cash, is my 401(k) safe in a crash and advisor or do it yourself.
One question for this week: what is your mortgage rate, exactly? Many people are off by half a point or more, and the whole decision turns on it.
As always, if you want to talk any of this through, the door is open. Genti