401k Math: What You're Actually Saving

Maxing Your 401k Doesn’t Cost What You Think

The number that kills people is $23,500. That’s the 2026 employee contribution limit for a 401k. People look at that, do a quick mental calculation, and decide they can’t afford to max it.

They’re wrong. And the math is embarrassingly simple.

If you’re in the 35% marginal tax bracket — which describes a lot of senior engineers and tech workers — maxing your 401k doesn’t cost $23,500 out of pocket. It costs you about $15,275.

The other $8,225? That’s money you would have handed to the IRS anyway. You’re just rerouting it to your future self instead.

Here’s the math: every dollar you contribute to a traditional 401k reduces your taxable income by one dollar. At a 35% marginal rate, that means your take-home pay only drops by 65 cents for every dollar contributed.

$$23,500 \times (1 - 0.35) = 23,500 \times 0.65 = $15,275$$

You put $23,500 into a tax-advantaged account. Your paycheck only drops by $15,275 for the year. The federal government effectively co-funded $8,225 of your retirement savings — money that would have vanished in taxes regardless.

This isn’t a trick. It’s the entire point of tax-deferred accounts.

The 2026 Contribution Limits

Before the math gets more interesting, here are the actual numbers:

Employee contribution limit: $23,500
This is what you personally can contribute through payroll deductions.

Total limit (employee + employer): $70,000
If you include employer contributions — matching, profit sharing, after-tax contributions — the combined limit is $70,000. This is the ceiling you’re working toward with strategies like the mega backdoor Roth.

Age 50+ catch-up: $31,000
If you’re 50 or older, your employee contribution limit jumps by $7,500, to $31,000. This was indexed upward in recent legislation. If you’re approaching that birthday and thinking about retirement timing, factor this in.

These limits reset every year, so unused space doesn’t roll over. January 1st is the official start of a new opportunity to contribute; your HR system might need to be updated manually.

The Employer Match: Genuinely Free Money

Your employer match is the closest thing to a 100% guaranteed return that exists in personal finance. It’s not a metaphor. It’s arithmetic.

A common match structure: 50% match on up to 6% of salary. Let’s run that on a $150,000 salary:

• 6% of $150k = $9,000 (your contribution)
• 50% match = $4,500 (employer contribution)
• Total invested: $13,500
• Your actual out-of-pocket cost at 35% bracket: $9,000 × 0.65 = $5,850

You contributed $5,850 in actual take-home cost. You got $13,500 invested. That’s a 130% immediate return before a single market move.

Declining to contribute enough to capture the full match is one of the few genuinely irrational moves in personal finance. You’re turning down compensation that’s already been budgeted for you. If your employer offered to deposit $4,500 into your account in exchange for nothing, you’d take it. That’s what’s happening here.

First rule of 401k optimization: always contribute at least enough to capture the full employer match. Everything else is secondary.

Traditional vs Roth 401k: The Decision Framework

Most plans now offer both options. The choice is less complicated than people make it:

Traditional 401k

• Contribution is pre-tax — reduces your taxable income now
• Money grows tax-deferred
• Withdrawals in retirement are taxed as ordinary income

Roth 401k

• Contribution is after-tax — no reduction in taxable income now
• Money grows tax-free
• Qualified withdrawals in retirement are tax-free

The decision hinges on one question: will you be in a higher or lower tax bracket when you retire?

If you expect a lower bracket in retirement → Traditional wins. You get the deduction at your higher current rate and pay taxes later at a lower rate. Net benefit: positive.

If you expect a higher bracket in retirement → Roth wins. You pay taxes now at your current lower rate and avoid them later. Net benefit: positive.

For most high-earning tech workers — earning $150k-$400k+ in peak years, planning to withdraw $80k-$120k/year in retirement — the math tends to favor Traditional. Your marginal rate today (likely 32-37%) is probably higher than your effective rate in retirement. The deduction is worth more now.

That said, there are good reasons to lean Roth:

• Tax rate uncertainty. Nobody knows what Congress does in 20 years. A Roth is a hedge against higher future tax rates. Some tax diversification — part Traditional, part Roth — is a reasonable position.
• Long time horizons. If you’re in your late 20s or early 30s, the tax-free compounding on a Roth over 35+ years can be substantial.
• No RMDs on Roth. Traditional 401ks have required minimum distributions starting at age 73. Roth 401ks (when rolled to a Roth IRA) do not. This matters for estate planning and flexible withdrawal strategies.
• Current bracket is actually low. If you’re in a lower-income year — job transition, parental leave, sabbatical — a Roth contribution in that year is relatively cheap.

If you’re truly uncertain, splitting contributions between Traditional and Roth is a valid hedge. You’re not required to pick one. Most plans let you split the allocation however you want.

What About the Mega Backdoor Roth?

If your plan supports after-tax (non-Roth) contributions and in-service distributions or in-plan Roth conversions, you may be able to contribute significantly more than the $23,500 employee limit — up to the $70,000 total limit after accounting for employer contributions.

This is called the mega backdoor Roth, and it’s a legitimately powerful strategy for high earners who’ve already maxed their employee contribution. The mechanics are more involved, but the tax-free compounding upside is real.

Check your Summary Plan Description (the SPD document — HR has it) to see if your plan supports it. About 40% of large employer plans do.

What People Actually Get Wrong

1. Contributing 6% because the default enrollment was 6%

Fidelity and Vanguard default enrollments are set to capture the match, not to optimize your retirement. If you got auto-enrolled at 6%, that’s a floor, not a target. Log in and check.

2. Not contributing because “I’ll invest on my own”

This logic fails on the math. The 401k gives you a tax deduction you don’t get in a taxable brokerage. Investing $23,500 in a brokerage doesn’t save you $8,225 in taxes. Contributing to a 401k and then investing the tax savings in your brokerage is strictly better than just investing in a brokerage directly.

The only arguments for maxing taxable first are (a) you need flexibility to access the money before 59½ without penalty, or (b) you plan to use Roth conversion ladders and need the taxable account as a bridge. Those are real strategies. “I’ll just invest on my own” usually isn’t.

3. Forgetting to increase contributions after a raise

You got a 10% raise. Your contribution percentage stayed the same. In dollar terms, you’re contributing more — but you’re also earning more, so the match basis went up too. Check whether you’re still capturing the full match percentage, and consider whether you can close the gap to the $23,500 limit.

4. Not contributing at all in the first year

New job jitters, benefits overwhelm, “I’ll get to it.” Every missed pay period is a month of tax-deferred compounding you never get back. If you just started a job, open your 401k portal today. You can start contributing before you’ve figured everything else out.

The Actual Cost at Different Tax Brackets

Not everyone is in the 35% bracket. Here’s the real out-of-pocket cost to max your employee contribution at common marginal rates:

Even at 22%, you’re putting $23,500 in retirement savings while your paycheck only drops by $18,330. The federal government is co-investing alongside you at every bracket.

State taxes amplify this. If you’re in California at 9.3%, add that to your federal rate. A California resident in the 35% federal bracket has a combined marginal rate of roughly 44%. At that rate, maxing the 401k costs them $13,160 in take-home pay — and shelters $10,340 from taxes.

The Action Item

All of this math is useless if you don’t log in and change your contribution percentage.

Here’s what to do today:

1. Log into your 401k portal (Fidelity, Vanguard, Schwab, Empower — wherever your employer uses)
2. Find your current contribution percentage
3. Make sure it’s at least high enough to capture the full employer match
4. If you can afford it, increase toward the $23,500 annual limit

The limit resets every January. If you start at 8% when you should be at 15%, the only way to catch up is to increase your percentage now, not later.

Your paycheck will drop less than you expect. The math says so.