How a 401(k) match actually works, and why it comes first

The screen Joe gets on his fourth day says “Congratulations on your benefits eligibility,” and one box is already filled in: 3%. That 3% is not what his employer is putting in. It is how much of Joe’s own pay the plan will route into his 401(k) every payday, pre-filled by automatic enrollment, which starts a new hire saving unless they say otherwise. He clicks confirm, feels responsible, and does not think about it again for two years.

Here is what the screen did not mention: his employer matches whatever Joe puts in, dollar for dollar, up to 6% of pay. So Joe’s 3% collects a 3% match, and the three points he never claimed simply go uncollected. Nothing dishonest happened to him. The full offer stayed open the whole time, at the number the plan published, and his employer added every dollar the formula required. The default in the box was just chosen by somebody else, for reasons that were never Joe’s finances, and he read it as a recommendation.

The usual way this subject gets taught is a two-word slogan, free money, and the slogan is true as far as it goes. But free money is a description of the price, not the product, and it explains none of the decisions that determine what you actually collect. A 401(k) match is better understood as a contract. It has a formula, a cap, a payment schedule, and a forfeiture clause, all published in a document your employer is legally required to hand you, and the entire distance between collecting all of it and collecting half of it, which is Joe’s distance, is ten minutes with those terms. This article reads them in order. The argument for why the match outranks everything else on a payday is made in what to do with your money first and I will not re-argue it here; this is the owner’s manual for the thing itself.

The formula and the cap decide your number

Every match has two moving parts: how much the employer adds per dollar you contribute, and where the adding stops. A plan that matches “100 percent of the first 4 percent of pay” adds a full dollar for each of your dollars until your contributions reach 4% of your salary, then adds nothing for further dollars. A “50 percent up to 6” plan adds half-dollars along a longer runway. Some plans stack tiers, a full match on the first slice and a half match on the next. Across the 755 plans in the Plan Sponsor Council of America’s latest annual survey, covering the 2024 plan year, employer contributions averaged 4.8% of pay, which is real money: on a $60,000 salary, about $2,880 a year that exists only if claimed.

The cap is the number that should set your contribution floor, and this is where the figure matters more than the prose:

Read your own plan’s version of that line, because the default in your enrollment screen has no obligation to sit on it. Automatic enrollment is now the norm rather than the exception, in 64% of plans per the same PSCA survey, and it has been a genuine good: people who would never have filled in the box get enrolled by inertia instead of excluded by it. The mechanism is exactly as plain as it sounds, in the Department of Labor’s own description of these plans: employees “are automatically enrolled in the plan and a specific percentage will be deducted from each participant’s salary unless they opt out or choose a different percentage.” That last clause is the whole opportunity. The percentage is yours to set, and the default rate and the match cap are chosen separately, sometimes years apart, with nothing forcing them to agree. When they disagree, the gap between them is Joe’s situation: a contribution that feels finished, sitting below the line the plan itself drew.

If you take one action from this article, it is this: find the cap, and set your contribution rate at it or above it. If the budget genuinely cannot reach the cap this year, get as close as it allows and revisit at every raise. Every point below the line is that point’s match forfeited, and forfeited is the right word, because unclaimed match from a paycheck does not wait for you. It simply never existed.

Two clarifications that spare people real confusion. First, the match is the employer’s money, not a withdrawal from your own contribution allowance: the matched dollars ride alongside whatever you were already allowed to put in, which means collecting the match never crowds out your own saving. Second, if your plan offers a Roth option and you use it, check where the match itself lands, because in many plans the employer’s side is deposited as pre-tax money even when your contributions are Roth, so the two halves of the same account will be taxed differently on the way out decades from now. Neither detail changes what you should do this week. Both change what the account statement means when you read it.

The timing trap almost nobody mentions

Here is the term that surprises even careful people: most plans compute the match per pay period, not per year. Each paycheck, the employer matches that paycheck’s contribution up to the cap’s share of that paycheck’s pay. Contribute evenly all year and the distinction never matters. Contribute unevenly and it can quietly cost a fortune.

Here is one example, with the arithmetic run all the way through. Laura earns $96,000 at a plan matching dollar for dollar up to 4% of pay. Determined to get her saving done early, she contributes heavily from January and stops at midyear, having put in everything she planned for the year. Every paycheck from January to June was matched, but only up to 4% of that paycheck’s pay, so her match ran on half a year of salary: 4% of $48,000, which is $1,920. From July to December she contributes nothing, and a per-period plan therefore matches nothing. A coworker on the identical salary at the identical plan spreads the same saving evenly and collects 4% of every paycheck all year: 4% of $96,000, which is $3,840. Same salary, same plan, same money saved, and Laura receives half the match, not because she saved less but because she saved on the wrong schedule.

A cousin of the same trap lives in bonus season: whether a bonus check gets matched depends on how your plan defines the pay it matches, and plans differ. Someone counting on a December bonus to carry their contribution rate over the line can discover in January that the plan’s definition never included it.

Some plans repair the front-loading version of this with a year-end true-up, recalculating the match on annual totals and depositing the difference. Some do not, and nothing on the enrollment screen tells you which kind you have. The answer lives in the summary plan description, the plan’s actual contract, which federal law requires your employer to provide. The Department of Labor’s guidance for plan participants is worth knowing about generally: the law “sets minimum standards for participation, vesting, benefit accrual and funding,” and the documents it obligates your plan to furnish are where every term above gets its real values. For most people the practical lesson is simpler than the paperwork: an even contribution rate, held all year, collects every matched dollar in every plan design, true-up or not.

The forfeiture clause: vesting, in real numbers

The match arrives in your account, and for a while it may not be entirely yours. Vesting is the schedule on which the employer’s contributions become permanently your property, and federal law caps how slow that schedule may be:

The DOL’s own sentence on the first row is the one to keep: “You immediately vest in your own contributions and the earnings on them.” Nothing your employer decides can touch the money you put in. The match is different, and the schedule turns out to be career information, not just financial information: someone eleven months from a cliff date is holding a five-figure reason to know exactly where that date falls, and someone comparing job offers can treat a generous vesting schedule as the compensation it quietly is. If you leave before vesting completes, the unvested portion returns to the plan, which does not make taking a better job wrong. It makes the date worth knowing before you pick a start date, because a resignation letter sent three weeks early can be the most expensive letter a person ever writes.

The measured cost of ignoring all this

If the terms above feel like fine print, here is what fine print costs at national scale, from one of the cleanest experiments in household finance. Economists James Choi, David Laibson and Brigitte Madrian went looking for unambiguous mistakes in 401(k) behavior, and found a population that made the test airtight: employees old enough to withdraw contributions penalty-free, at seven companies with a match. For them, contributing below the cap has no honest defense: deposit, collect the match, withdraw the deposit if you like, keep the difference. The paper’s abstract reports what happened anyway: “between 20% and 60% contribute below the threshold, losing as much as 6% of their annual pay.” And then the sentence that should end every argument that this is an information problem: “Providing employees with information about the free lunch they are foregoing fails to raise contribution rates.”

I find that last finding clarifying rather than depressing. If information alone fixed this, the slogan would have fixed it years ago, since everyone has heard the slogan. What actually collects the match is not knowing about it but automating it: one visit to the portal, contribution rate set at or above the cap, and the terms of the contract execute themselves every payday for years, whether or not you ever feel motivated again. The people who collect their full match are not more disciplined than the people in that study. They changed a setting once.

Ten minutes, start to finish

The whole owner’s manual compresses to this. Log into the benefits portal and open the plan summary. Find the match formula and its cap; set your rate at the cap or higher, and if money is tight, as close as the month allows, raised at every raise. Check whether the match computes per paycheck and whether a true-up exists, and if you ever front-load contributions, check twice. Note your vesting schedule and the date the match becomes fully yours, and let that date into any job-change arithmetic. Then close the portal.

Joe, from the opening, eventually did the ten minutes, in his third year, after a coworker mentioned the word cap in a lunch line. Moving the 3 to a 6 took one screen. The part that stays with him is not the money he collects now, but the two years of half-collected match that no form can retrieve, forfeited a paycheck at a time by a number he never chose. The contract had been offering the full amount all along. It was waiting for him to read it.