

There are two things missing from that calculation. First, the mortgage savings are generally after tax, while investment gains are taxable. So the comparison of break even needs to take this into account.
Long term taxation on investments is 15%. So, at a 2.85 interest rate we’re still talking about 3.3% ROI. I can beat that buying a US Treasury Bond.
Secondly, if pay off the mortgage earlier, then you have some number of years at the end where you can then invest the entirety of your payment instead of paying mortgage.
But you’ve foregone all the income returns in the initial years that you failed to invest in the market.
Let’s be conservative and predict a 7% market ROI (right now, the markets are doing closer to 25% YOY). If my options are $1100 mortgage payment over 25 years or $1000 over 30 years, I’m looking a 25 years of $100/mo savings ($1200/year -> 25 years = $30,000). By the time you’ve paid off your mortgage, my accrued investment returns amount to around $78k. So we’re going into year 26. I’ve got $78k in investment principle, at 7%/year, earning me $5400/year. That’s nearly half my mortgage note. You’re putting your first $1100/mo => $13,200/year into savings, having missed 25 years of compounded returns.
Up the ROI from 7% to 10% (the historical DOW return over the last 30 years), and now I’ve got $123k in principle, earning $12,300/year, which is more than the mortgage note.
The excess you’re paying into the mortgage is effectively an investment with a yield equal to your interest rate. If you were paying an 11% note, getting rid of your mortgage quickly makes sense. But at 3%, it does not.
The raw math becomes ($mortgage payment)(ROI - Interest Rate) = Implicit Return.
The last thing isn’t numbers, really. You can live in a house, you cannot live in an investment account
In both scenarios, we’re living in the house. The amount you pay on the note doesn’t change that.
Not to mention the discipline bit that you mentioned.
That’s where the math ultimately gets fuzzy. Are you actually banking the $100/mo in mortgage savings as investment? Or are you just shoving it in your savings account and forgetting about it? Or spending it?
I find that periodic automatic transfers do a lot of this book-keeping for me. 401ks come out of my paycheck before it hits my savings account. I’ve got an automatic monthly deduction for my son’s 529 and my Roth IRA. And I try to do a sweep from my savings to investments roughly once a month, when I’m over a certain cash balance.
But I’ll concede all this requires a certain surplus income. If you’re stuck living paycheck to paycheck, its possible that paying down the mortgage faster is just less of a headache than juggling balances to make sure ends meet.








Today, certainly. Back in 2020 when we were entering the COVID-induced recession, the prime rate plunged back into ZIRP territory and you could refinance a mortgage incredibly cheaply.
Generally speaking, your options are 15 year or 30 year (at least in the US). The difference in interest rates is typically marginal, though. Maybe .5 pt, from what I’ve seen. The real perceived benefit is paying off the debt faster. But… again, if the loan is large and the interest rate is small, you’re putting a lot of cash behind a comparatively low return.