Retirement accounts
How Much Should You Contribute to a 401(k)? The One Rate With an Objective Answer
There is one 401(k) contribution rate with an objective answer: the employer match cap. Below it you decline pay. Above it, arithmetic gives way to preference.
Most articles answer this question with a percentage. A percentage is a recommendation, and a recommendation about your money is something a registered adviser gives after learning your tax bracket, your debts, your job security and your timeline. This site publishes research, not advice, so it will not hand you one.
What can be settled here is narrower, and more useful than it sounds. Exactly one 401(k) contribution rate has an objective answer, and it is the point where your employer stops matching. Below that point you are turning down compensation already budgeted for you. At or above it, every further dollar is a trade between money now and money later, and no plan document decides that for you.
The only rate with an objective answer is the match cap
Plans do not match your contribution. They match a capped fraction of it. The formula written into almost every plan document reduces to one line:
match = min(your deferral rate, the cap) × match rate × salary
Three inputs, two of which belong to the employer. The most common single-tier formula pays 50 cents per dollar on the first 6% of pay. The cap is 6%, the match rate is 50%, and your deferral rate is the only term you control. The min() is doing all the work.
Below the cap the function is linear, so every percentage point you skip carries a price. On a $75,000 salary under that formula the full match is $2,250 a year. Defer 3% and you collect $1,125. The other $1,125 is not delayed, not invested elsewhere, and not recoverable later. It was set aside for you and went unclaimed.
Above 6% the line goes flat. The seventh percentage point of deferral buys exactly as much match as the eleventh, which is none. That flat stretch is where every judgement call lives, and it is where this article stops answering.
The match is compensation, not a bonus
Framing it as a windfall makes it easy to skip. Framing it as part of the wage bill makes the arithmetic obvious: an employer offering 50%-to-6% has budgeted 3% of your salary and pays it only if you claim it. Two caveats before you count it as yours. Some plans use a tiered formula, such as 100% on the first 3% and 50% on the next 2%, which moves the kink. And the match may sit on a vesting schedule, which means an unvested match is money in your account that you do not own yet.
The ceiling, and who it belongs to
Section 402(g) caps what you may defer from salary in a calendar year. These are the 2026 figures.
| Age reached during 2026 | Catch-up available | Total elective deferral limit |
|---|---|---|
| Under 50 | None | $24,500 |
| 50 to 59 | $8,000 | $32,500 |
| 60 to 63 | $11,250 | $35,750 |
| 64 and over | $8,000 | $32,500 |
The 60 to 63 tier comes from SECURE 2.0 and it is a four-year window, not a permanent step up. The higher catch-up applies in the calendar years you are 60, 61, 62 and 63, then reverts.
The structural point matters more than the numbers: the limit is per person, not per plan. Change jobs in June and the deferrals you made at the old employer count against the same ceiling as the ones you make at the new one. A second plan adds no room at all. Neither recordkeeper can see the other, which makes the running total your arithmetic to keep. What happens to the old 401(k) when you leave the job is a separate question, but the deferral tally follows you across the change.
Two things sit outside this ceiling. The employer match is one: it is not an elective deferral, so it does not consume any of your limit, and it is instead bounded by the much larger annual additions cap that covers everything credited to the account. A governmental 457(b) is the other, and public-sector workers who have one get a second ceiling that does not aggregate with the 401(k), where that larger cap is set out with its 2026 figure.
What a deferral actually costs your paycheck
Deferring 6% of pay does not reduce take-home by 6% of pay. A pre-tax deferral of X removes X from the wages subject to income tax withholding, so take-home falls by X(1 − t), where t is your marginal income tax rate.
On a $75,000 salary paid every two weeks, 6% is $173 a paycheck. At a 22% combined marginal rate, take-home falls by $135. The missing $38 is withholding that no longer applies.
A designated Roth deferral behaves differently. It comes out of after-tax pay, so take-home falls by the full $173 and the account grows tax free instead. Same plan, same limit, different point of taxation. The comparison between a Roth workplace account and a Roth IRA covers where the two diverge on access and rules.
One thing neither treatment changes: Social Security and Medicare tax. An elective deferral is excluded from income tax at the time of deferral and stays in the wage base for FICA. The saving is income tax only, and only on the pre-tax side.
What happens if you contribute too much
Deferrals above the 402(g) limit are excess deferrals. Inside a single plan this rarely happens, because the recordkeeper stops the deferral when the limit is reached. Across employers it happens easily. An unrelated plan has no visibility into what you deferred somewhere else, so a mid-year job change is where the tally goes wrong.
The fix is a distribution. The excess, plus the earnings attributable to it, has to leave the plan by April 15 of the year following the year of the deferral. You request it from one of the plans, and either one will do.
Miss that date and the amount is taxed twice: once as income in the year you deferred it, and again when it eventually comes out of the plan. Leaving it alone does not correct it. The money sits in the account with no tax basis, waiting to be taxed a second time on the way out, and no later distribution undoes that.
Can you change your 401(k) contribution at any time?
There is no federal rule setting how often you may change your deferral rate. The regulation sets a floor and nothing above it: an employee must have an effective opportunity to make or change a cash or deferred election at least once during each plan year. Everything beyond that minimum is the plan's decision, written into the plan document.
In practice most large recordkeepers now let you change the rate online whenever you like, effective with the next payroll that has not yet been processed. Narrower plans still exist. Quarterly change windows are not rare, and a few plans restrict elections to an annual enrolment period.
Stopping is an election too
Dropping to 0% is a deferral election like any other and follows the same plan rules for timing. One mechanism is worth checking first: whether the match is calculated pay period by pay period. If it is, a quarter spent at 0% is a quarter with no match, and no year-end adjustment brings it back. That same mechanism is what makes the opposite move expensive.
Front-loading, and the true-up your plan may not have
Reaching the annual limit by August sounds efficient. In a plan without a true-up it costs money, and the mechanism is worth understanding before you set a high rate.
Most plans compute the match one pay period at a time, on that period's own deferral, against a per-period version of the cap. Defer hard and you hit $24,500 in August, at which point the deferral stops. With no deferral there is nothing to match, so the match stops with it. The heavy deferrals earlier in the year did not earn extra match either, because each of them was already above the per-period cap.
A true-up provision fixes this. At year end the plan recalculates the match as though your deferrals had been spread evenly and deposits the difference. Many plans have one. Many do not, and the plan document is the only place that says which.
The loss is bounded by the match you would have earned in the pay periods you sat out, and it scales with how early you finish. On the same $75,000 salary and 50%-to-6% formula, the per-period match is $86.54. Finish in mid-August, around period 16 of 26, and the ten idle periods forgo roughly $865. Finish in late November instead, at period 22, and four idle periods cost about $346. The paycheck module runs both schedules across every deferral rate, so the gap can be read against your own plan rather than against this example.
Above the cap there is no formula, only a trade
Past the match cap the question changes shape. Every additional dollar deferred is a dollar not spent, and the terms of that trade are your marginal rate today against your expected rate in retirement, the cash you hold against an emergency, the interest you pay on debt, and how stable your income is. Whether an HSA offers better tax treatment than either 401(k) flavour belongs in the same comparison. None of those are in this article, because none of them are knowable about a reader.
The by-age benchmarks that circulate run into the same wall. "How much should you have saved by 30" is not answerable in general, because the answer is a function of when you started, what you earn, what you will spend and how long you will work. A number that ignores all four is a number about somebody else.
Something adjacent is answerable, though, and it gets less attention than it deserves. The plan is not neutral about what happens to the dollars once they arrive. Fund expenses inside the plan menu compound against the balance the same way the balance compounds for you, and unlike the contribution rate, that one has a defensible direction.
Below the match cap the arithmetic is settled and the money is already yours to claim. Above it there are constraints worth knowing and no formula that resolves them, and the choice inside those constraints belongs to the person making it.