The math behind this calculator (click to expand)
Each year, the projection grows the balance by the assumed return rate, then adds the year's employee contribution (capped at the IRS deferral limit) plus the employer match. The compact form is balance_next = balance * (1 + r) + employee_contrib + employer_match, run for each year from your current age to retirement.
Employee contribution is the lesser of (a) your contribution percentage applied to that year's salary, or (b) the IRS deferral limit for your age that year ($23,500 base in 2026, $31,000 with the age-50 catch-up, $34,750 with the SECURE 2.0 super catch-up at ages 60-63). Salary grows at the salary-growth rate compounded annually. Employer match is calculated against the salary and capped at the match-percent threshold. The combined Section 415 limit ($70,000 for 2026) is enforced for the total of employee plus employer plus any after-tax contributions.
Implementation by Michael.
The $23,500 Limit and Why It Matters Less Than You Think
The 2026 employee deferral limit of $23,500 sounds like a hard ceiling, but it only caps your contributions. Employer matching goes on top - a 50% match on 6% of a $175,000 salary adds another $5,250 annually that doesn't count against your limit. And if your plan supports after-tax contributions with in-plan Roth conversions (the "mega backdoor Roth"), the combined Section 415 limit for 2026 is $70,000. That's the real ceiling.
For someone earning $150,000 and contributing 15% ($22,500, just under the limit), the tax savings in a traditional 401(k) are immediate: at a 24% marginal rate, that's $5,400 less in federal income tax this year. Over 35 years, the compounding difference between pre-tax and after-tax investing is substantial - roughly $180,000 on that contribution level alone, assuming 7% returns and annual tax drag of 0.3% in a taxable account.
Catch-Up Contributions: The Age-50 Bonus
Starting the year you turn 50, you can defer an extra $7,500 beyond the standard $23,500 - $31,000 total for 2026. Over 15 years (age 50 to 65), that additional $7,500/year at 7% returns compounds to approximately $188,000. If your employer also offers a match on catch-up contributions (not all do), the value is even higher.
There's a timing nuance: catch-up eligibility is based on the calendar year you turn 50, not your birthday. If you turn 50 on December 31, 2026, you can contribute $31,000 for all of 2026. SECURE 2.0 also introduced a "super catch-up" for ages 60-63 starting in 2025 - an additional $3,750 on top of the standard catch-up, bringing the total to $34,750 for that narrow age window. This calculator uses the standard catch-up; adjust your contribution percentage if you qualify for the super catch-up.
Employer Match: Capture Every Dollar
Not contributing enough to get the full employer match is the most expensive mistake in retirement planning. A common formula - 50% match on the first 6% of salary - means you need to contribute at least 6% to capture the full 3% employer contribution. On a $120,000 salary, that's $3,600/year you'd forfeit by contributing only 5% instead of 6%.
That $3,600/year in missed match, compounded at 7% over 30 years, grows to roughly $340,000. It's not hyperbole to call the employer match the highest guaranteed return available - you earn an instant 50-100% return on matched contributions before any market growth. Even if you're carrying moderate-rate debt (say, 5-6%), contributing up to the full match typically wins because the match return exceeds your debt interest rate on day one.
Tax-Deferred Growth: The Compounding Advantage
A 401(k)'s tax deferral means dividends, interest, and capital gains compound without annual tax drag. In a taxable brokerage account, a 2% dividend yield taxed at 15% costs you 0.3% in annual returns. That sounds minor, but over 35 years on a $500,000 portfolio, it's the difference between $5.34M and $5.07M - roughly $270,000 in lost growth.
The tradeoff: you pay ordinary income tax on traditional 401(k) withdrawals. If your effective tax rate in retirement is 22%, that $5.34M is worth roughly $4.17M after tax. The taxable account's $5.07M has already been taxed on dividends, but unrealized gains face capital gains tax (currently 15-20%) on sale. For most people in the 22-32% bracket during peak earning years, the math favors maxing the 401(k) first - especially if your retirement tax rate will be lower due to reduced income.
Running Your Own Scenario
Start with your actual numbers: current balance from your latest 401(k) statement, your gross salary, and your plan's match formula (check your Summary Plan Description or HR portal). A 35-year-old earning $135,000 with $87,000 already saved, contributing 12% with a 50% match on 6%, and a 7% return would project to approximately $2.8M by age 65. Dropping the contribution from 12% to 6% - still capturing the full match - reduces the projection to about $1.9M. That 6-percentage-point difference in contribution rate represents nearly $900,000 in retirement.
Adjust the salary growth slider to model promotions and raises. At 3% annual growth, a $135,000 salary becomes roughly $380,000 by age 65. Once that growing salary pushes your dollar contributions above the $23,500 limit, the calculator automatically caps your deferral - and you'll see the effective contribution rate drop below your target percentage. That's the IRS limit doing its work, and it's one reason high earners explore the mega backdoor Roth for additional tax-advantaged savings.
What might change in the next 24 months
Three pieces of legislative gravity will shape the 401(k) math next. The IRS deferral limit is annually inflation-indexed in $500 increments: it stepped from $23,000 in 2024 to $23,500 in 2025 and 2026, and the next move (likely 2027) is expected to be $24,000 if CPI growth continues at 2.5 to 3% (IRS Notice cadence). The Section 415 combined limit moves with it, which expands the effective ceiling on the mega backdoor Roth.
SECURE 2.0's "super catch-up" for ages 60-63 took effect in 2025 ($3,750 above the standard $7,500 catch-up). Higher-paid catch-up contributors (those whose prior-year W-2 wages exceed $145,000, indexed for inflation) must make catch-up contributions to the Roth bucket starting in 2026, per SECURE 2.0 Section 603. That's a quiet but consequential shift: it eliminates the upfront federal deduction on catch-up contributions for many high earners. Worth knowing if you're 50+ and earning above the threshold.
Mandatory automatic enrollment for new 401(k) plans (also SECURE 2.0) phases in beginning 2025, with default contribution rates between 3 and 10% and 1% annual auto-escalation up to at least 10%. This affects new plans, not the existing one you're modeling, but it's reshaping the baseline savings rate across the workforce.