HSA vs. 7% Mortgage Paydown vs. a $300 Bank Bonus: Where Your Next $5,981 Goes at the 24% Bracket (September 2026)
Here is a scenario I keep running into. A family at the 24% federal bracket has $8,750 of room in a 2026 family HSA. They have a mortgage. NerdWallet's September 28 rate report says rates fell a bit that day but are "still solidly above 7%." Their bank is also advertising a signup bonus. And everyone at work is talking about whether an AI bubble is about to wreck their retirement accounts.
So where should the next dollar go? I ran the numbers, and the answer depends on four inputs of yours. Below I lay out the comparison so you can see which inputs matter.
The Backdrop: What September 2026 Data Actually Says
Here is what the source articles give us to work with:
- Mortgage rates: NerdWallet's September 28 update puts rates "solidly above 7%." Paying down a 7.1% loan is a guaranteed 7.1% return, taxed at nothing if you don't itemize.
- Inflation: The Bureau of Labor Statistics shows CPI +0.4% in August 2026.
- Jobs: Unemployment is 4.1%, payrolls rose 162,000 (preliminary), and average hourly earnings rose just $0.10.
- Markets: Mr. Money Mustache's "Will the AI Bubble Destroy our Retirement?" is about how we react when stocks hit record highs and when they crash. That reaction matters for HSA investing, and I come back to it below.
- Bank bonuses: NerdWallet's "Should I Switch to a New Bank Just to Earn a Bonus?" says bonuses "usually take some effort to earn." That is the right lens for comparing them with a tax deduction.
A $0.10 raise is about $208 a year for a full-time worker (2,080 hours). Meanwhile a 0.4% monthly CPI print on a $6,000 household budget (my example figure) is about $24 a month in extra cost. Wages and prices are moving at different speeds. That is why a guaranteed tax reduction looks more attractive than usual, and why it's worth checking that you can afford to lock the money up.
Step 1: What $8,750 Really Costs You
The 2026 HSA limits are $4,400 for self-only coverage and $8,750 for family coverage, plus a $1,000 catch-up at age 55 or older. Most people quote the income tax deduction and stop there. If you contribute through payroll, you also skip FICA (7.65%).
Worked example (24% federal bracket, payroll contribution, no state tax):
| Item | Amount |
|---|---|
| Family HSA contribution | $8,750 |
| Federal income tax saved (24%) | $2,100 |
| FICA saved (7.65%) | $669 |
| Total year-one tax savings | $2,769 |
| Effective after-tax cost | $5,981 |
That $5,981 is the number to use when comparing against other uses of cash. You are comparing $5,981 of take-home pay against $8,750 of HSA money. Add a 5% state income tax and the savings grow to about $3,207, which is the year-one figure I've used in the true cost of skipping your HSA max. Self-employed readers don't skip FICA the same way. See the self-employed HSA deduction math for that difference.
Step 2: HSA vs. a Mortgage Above 7%
This is the hardest comparison, because the mortgage side is a certain return and the HSA side is not.
The setup: You have $5,981 of after-tax cash. You can put it toward a 7.1% mortgage, or you can contribute $8,750 to the HSA and invest it. I'm assuming you don't itemize, so the mortgage interest you save is not reduced by a deduction. I'm also assuming the HSA money is later used for qualified medical costs, so the growth is never taxed.
- Mortgage paydown: $5,981 × 1.071³⁰ ≈ $46,830 after 30 years. (Interest saved is assumed to be reinvested at the same 7.1%.)
- HSA at 7% growth: $8,750 × 1.07³⁰ ≈ $66,606 after 30 years.
The HSA wins by roughly $19,800 in that scenario. But what growth rate makes the two equal? Solve 8,750 × (1 + r)³⁰ = 46,830 and you get r ≈ 5.75%.
| HSA average annual return | HSA value after 30 years (one $8,750 deposit) | vs. mortgage paydown ($46,830) |
|---|---|---|
| 4.0% | $28,380 | Mortgage wins by $18,450 |
| 5.75% | ~$46,830 | Break-even |
| 7.0% | $66,606 | HSA wins by $19,776 |
| 8.0% | $88,050 | HSA wins by $41,220 |
Read this honestly: if your HSA sits in cash or a very conservative allocation earning 4%, the mortgage beats it. If you invest the HSA in a diversified stock-heavy mix and reach even a mid-5% return, the HSA comes out ahead. The mortgage payoff is guaranteed, and the HSA depends on how the market performs. Neither answer is right for everyone. For more break-even scenarios at different brackets, see the 5% break-even return and 5-gate checklist. This kind of side-by-side is what Trivexano runs for you, so you don't have to build the spreadsheet yourself.
Two more points that tilt the comparison:
- Liquidity. Money paid into a mortgage is locked in your house. HSA money stays available for qualified medical costs at any time, and after 65 it can be withdrawn for anything, taxed as ordinary income like a traditional IRA and with no 20% penalty.
- Your bracket. At 22% the HSA break-even return rises. At 32% it falls. The break-even I calculated applies to the 24% bracket only.
Step 3: HSA vs. a Bank Bonus
NerdWallet's guidance on bank bonuses is useful. They usually require direct deposits, minimum balances, or holding periods, and you have to weigh the effort. Here's the math with a hypothetical $300 bonus (an illustrative figure, not a specific offer):
| Bank bonus | HSA max | |
|---|---|---|
| Gross benefit | $300 | $2,769 (year-one tax savings) |
| Tax on the benefit | Interest income at 24% = $72 | None |
| Net benefit | $228 | $2,769 |
| Requirements | Direct deposit, balance minimums, account opening | HDHP coverage, eligibility |
| Ongoing value | Ends when you close the account | Growth stays tax-free |
These two choices aren't mutually exclusive. The bonus doesn't take the HSA's contribution room, and the HSA doesn't stop you from opening the account. The real question is whether the hours and minimum balance are worth $228. For a fuller version of this comparison, see the $300 bonus vs. $8,750 HSA math.
Step 4: 10, 20, and 30 Years of HSA vs. a Taxable Account
Now compare the HSA against putting the same $5,981 of after-tax cash into a regular taxable brokerage account every year. I assume 7% growth in both accounts and a flat 15% capital gains tax on the taxable account's gains at the end. This ignores dividend and fund-distribution taxes along the way, so the taxable account is being treated generously.
| Horizon | HSA value ($8,750/yr) | Taxable value ($5,981/yr, after 15% tax on gains) | HSA advantage |
|---|---|---|---|
| 10 years | $120,890 | $79,210 | $41,680 |
| 20 years | $358,706 | $226,354 | $132,352 |
| 30 years | $826,535 | $507,139 | $319,396 |
Total HSA contributions over 30 years are $262,500. Total after-tax cash into the taxable account is $179,430. The gap comes from three places: the upfront deduction, the FICA savings, and tax-free growth. For a lower-fee alternative view, the $826,000 30-year calculator shows how the four inputs (contribution, return, horizon, and tax bracket) change the outcome.
But your numbers will differ. A 5% return cuts the 30-year HSA figure to roughly $581,000. A 12% bracket cuts the upfront savings. If you have a chance to use the money for non-medical costs before 65, the tax and 20% penalty change the picture completely.
Step 5: Investment Allocation and the AI-Bubble Question
Mr. Money Mustache's piece on the AI bubble is about how we feel when markets hit records and when they crash. In HSA terms, the risk is not that stocks fall. The risk is that you sell after they fall.
Try a simple stress test with a $100,000 HSA balance (an example):
- A 40% drop takes it to $60,000.
- If you have a $6,000 surgery bill that year and pay it from the HSA, you sold at the bottom.
- If you paid the bill from your checking account, kept the HSA invested, and reimbursed yourself later, you lost nothing permanently.
That gives a practical way to set the allocation:
| Situation | Possible approach |
|---|---|
| 25+ years until Medicare, cash-flow secure | Stock-heavy HSA, with an amount equal to one year's deductible held in cash |
| 10 years to 65, some medical costs expected | Balanced mix, with cash covering the deductible and expected out-of-pocket costs |
| Within 5 years of 65 | Lower stock share, since you may soon draw on it for premiums and care |
| No cash buffer outside the HSA | Fix that first, since it forces you to sell HSA investments at a bad time |
Cash-only HSAs are the costliest mistake. See the $146,112 cost of leaving your HSA in cash for the 20-year comparison. That link corresponds to the post titled "The $146,112 Hidden Cost of Leaving Your HSA in Cash". The exact allocation that suits you depends on your medical-cost outlook and how you'd react to a 40% drop, not on the headline.
Step 6: The Medicare Rule at 65
This is where a lot of the plan falls apart. Once you enroll in any part of Medicare, you can no longer contribute to an HSA. There's also a trap: if you sign up for Medicare Part A after 65, and especially if you apply for Social Security, your Part A coverage can be backdated by up to 6 months. Contributions made in that window can trigger a 6% excise tax.
Here is a practical checklist:
- Stop contributions about 6 months before you plan to enroll in Medicare or start Social Security.
- Prorate your final-year limit by the months you're still eligible.
- Use the $1,000 catch-up from age 55 until you stop contributing.
- After 65, HSA withdrawals for Medicare Part B, Part D, and Medicare Advantage premiums are qualified and tax-free. Medigap premiums are not.
The full mistake is walked through in the $2,200 Medicare lookback mistake. Modeling that timeline alongside your contributions and investments at Trivexano is easier than tracking it by hand.
Which Wins? Four Variables Decide
| If this is true | Lean toward |
|---|---|
| Your mortgage is above 7% and you'd hold the HSA in cash | Mortgage paydown (after checking your emergency fund) |
| You're at 24% or 32% and can invest for 15+ years | HSA max |
| You're on a high-deductible plan with a thin emergency fund | Build the buffer first, then max the HSA |
| The bonus needs a big balance you'd move from elsewhere | Compare the after-tax $228 with the effort and any fees |
| You're within 6 months of Medicare | Stop contributing and use the remaining balance |
The four variables to plug in are your bracket, your mortgage rate, your realistic investment return, and your years to 65. Change any one and the winner can flip. For example, moving from the 24% bracket to 22% and expecting a 4.5% return would favor the mortgage. Moving to 32% and expecting 7% would favor the HSA by a wider margin.
I'd also be wary of any advice, including mine, that gives one answer for everyone. August's 0.4% CPI, a 4.1% unemployment rate, and a $0.10 wage gain all say your budget is under pressure, and the right plan may be to contribute less than the max for now. That's a legitimate result of the math.
Run Your Own Numbers
Before you move any money, write down the four inputs above and calculate three things: your after-tax cost of a contribution, the break-even return against your mortgage rate, and your last safe contribution date before Medicare. If you'd rather not build the spreadsheet, Trivexano lets you enter your own bracket, mortgage rate, allocation, and timeline and compares the outcomes side by side. Whichever way you go, decide with your own numbers, not with a rule of thumb.
This post is general education and uses illustrative examples, not personalized tax, legal, or investment advice. Check current IRS limits and your plan's eligibility rules before contributing.
Sources
- Will the AI Bubble Destroy our Retirement? — Mr. Money Mustache
- Mortgage Rates Today, Monday, September 28: A Little Lower, But Still Above 7% — NerdWallet
- Should I Switch to a New Bank Just to Earn a Bonus? — NerdWallet
- Major Economic Indicators Latest Numbers — Bureau of Labor Statistics
- This Tahoe Hotel Got a Glow-Up, but Missed a Few Spots — NerdWallet