401(k) Calculator

How this 401(k) projection works

A 401(k) is a payroll-deduction retirement account: a slice of every paycheck goes in before you ever see it, your employer often adds a match on top, and the combined pot compounds until you retire. This calculator turns your salary and contribution rate into a monthly deposit, adds the employer match — counted only up to your own contribution rate, because that is how nearly all match formulas work — and grows the total at your assumed return, compounded monthly.

Take the defaults: a $90,000 salary with a 10% contribution means you defer $750 a month, and a 4% match adds another $300. That $1,050 a month, compounding at 7% for 25 years, builds to roughly $855,537. Only $315,000 of that is money anyone actually deposited — the other $540,537 is investment growth, which is the whole argument for starting early and not interrupting the compounding.

Two honest caveats. First, the projection assumes a flat salary and a steady return; real life delivers raises (good) and bear markets (unpleasant but survivable), so treat the output as a planning anchor, not a promise. Second, the calculator takes a percentage but the IRS caps a dollar amount — $24,500 of employee deferrals for 2026 — so at higher salaries a big percentage will hit the ceiling before the year ends. More on that below.

The employer match is an instant 100% return

No investment on earth reliably doubles your money the moment you make it — except a dollar-for-dollar employer match. Contribute $300 and your employer deposits another $300: that is a 100% return before the market has done anything at all. On the default numbers, the 4% match is $3,600 a year of compensation you only collect by contributing. Skip it and your projected balance falls from about $855,537 to $611,098 — the free $90,000 of match money, once compounded, is worth roughly $244,439 at retirement. Whatever else your budget looks like, contributing at least up to the full match should be close to non-negotiable.

Match formulas vary, so read yours. Some employers match 100% of the first 4% of salary; others match 50% of the first 6% (which also totals 3% of salary but requires you to put in 6% to collect it); some cap the match in dollars. The calculator applies the simple, common structure — the match percentage of your salary, but never more than your own contribution rate — so if you contribute 3% against a 4% match, only 3% is matched.

One string attached: vesting. Your own contributions are always 100% yours, but employer money often vests on a schedule — either a cliff (nothing until, say, year three, then everything) or graded (a chunk each year over several years). Leave before you are fully vested and you forfeit the unvested match. If you are weighing a job change, check your vesting date first; walking out a few months early can quietly cost thousands of dollars of already-deposited match.

Traditional vs Roth, and the 2026 contribution limits

A traditional 401(k) contribution goes in pre-tax: it reduces this year’s taxable income, grows tax-deferred, and every dollar you withdraw in retirement is taxed as ordinary income. A Roth 401(k) flips the deal — you contribute after-tax money, get no deduction today, and qualified withdrawals in retirement come out entirely tax-free. The rough rule: if you expect a lower tax rate in retirement than today, traditional wins; if you are early-career and in a low bracket now, Roth is often the better bet. Many plans let you split contributions between the two, which is a perfectly sensible hedge against guessing wrong. Note the employer match is typically deposited pre-tax either way.

For 2026 the employee deferral limit is $24,500 (set in IRS Notice 2025-67), and workers aged 50 and over can make an additional catch-up contribution on top of that. The limit applies to your combined traditional and Roth deferrals across the year, and it is a dollar cap, not a percentage — 10% of a $90,000 salary is $9,000 and clears it easily, but 10% of a $300,000 salary is $30,000, and payroll will stop your deferrals once you hit $24,500. High earners who front-load should also check whether their plan has a true-up provision, because maxing out early in the year can otherwise cost match in the months after contributions stop.

Returns, fees and the cost of touching the money early

The default 7% is a deliberately sober assumption for a blended stock-and-bond portfolio held for decades — not a forecast of any particular year, in which returns will swing far above and below it. The right response to a bad year is usually nothing: contributions continue, buy shares at lower prices, and the long-run average does its work. Sliding the return input up to 10 or 12% makes the projection prettier and your plan worse; if a decision only works at optimistic returns, it is not a plan.

Fees compound against you exactly the way returns compound for you, and inside a 401(k) they hide in fund expense ratios and plan administration charges. The math is brutal at scale: the same $1,050 a month over 25 years grows to about $855,537 at 7% but only $731,282 at a net 6% — a single percentage point of annual fees swallows roughly $124,255 of your ending balance. You cannot control the market, but you can usually pick the low-cost index options on your plan’s menu, and that choice alone is worth more than most fund-picking cleverness.

Finally, treat the account as locked until age 59½. Pull money out of a traditional 401(k) early and you generally owe ordinary income tax on the withdrawal plus a 10% penalty — a combined haircut that can approach 40% for a middle-bracket saver, taken from money you also rip out of the compounding engine. There are exceptions and loans exist in many plans, but the default posture should be simple: money in a 401(k) is retirement money, and the calculator above shows why leaving it alone is so richly rewarded.