Does the Timing of Your 401(k) Contributions Matter?

Like a lot of the questions we chase at Passerine Finance, this one began as plain curiosity: if you put the exact same amount into your 401(k) every year, does it matter when during the year you contribute it? Money added in January has more months in the market than money added in December. Repeat that for a career, and how much could the timing alone really be worth?

To find out, picture two coworkers who each max out their 401(k). In 2026 the IRS lets an employee contribute up to $24,500, and both put in exactly that — not a dollar more, not a dollar less. They earn the same salary, get the same paychecks, and invest in the same fund. The only thing they do differently is the calendar.

The first, our front-loader, puts a large, steady amount in through the first half of the year and reaches the $24,500 limit by the end of June, then stops. The second, our even saver, does the ordinary thing: a slice every month, the same amount all year long, so the last dollar goes in with December's pay.

The Setup

Same dollars, two calendars.

We follow a household earning $180,000, paid monthly (12 pay periods a year), with 3% raises. Each year both savers contribute the IRS maximum, which we grow about 3% a year as the IRS typically does. Their employer offers a common match: 50% of the first 6% of pay, worth up to $5,400 in the first year. We run the whole thing for 20 years, over which — collected in full — that match adds up to about $145,100 in employer money.

We calculate the employee and the employer contributions for each month, just as an employer would, and invest each one at that month's actual market return. Following the money month by month is what surfaced the surprise — so let's do exactly that.

For the market itself we replay the most recent 20 years of real U.S. stock returns, from mid-2006 through May 2026 — a stretch that includes the 2008 crash, the long bull market, the 2020 COVID drop, and the recovery after. Over those two decades the broad market compounded at about 11.5% a year. Both savers ride that same rollercoaster; only their deposit timing differs.

The Math, Month by Month

Why the match stops for one saver and not the other.

The whole story is in the first-year breakdown. Paid monthly, this worker's gross pay is $15,000 a month. The match is 50% of the first 6% of pay — and 6% of $15,000 is $900 — so the most the employer will add in any single month is 50% of $900, or $450.

Both savers clear the 6% bar every month they contribute, so both earn the full $450 whenever they put money in. The catch is that phrase — every month they contribute. The even saver puts in $2,042 every month for twelve months and collects $450 twelve times: $5,400. The front-loader puts in twice as much, $4,083 a month, but reaches the $24,500 annual limit in June and then has to stop — so the match stops too. She collects $450 just six times: $2,700. Same $24,500 contributed; $2,700 less in free employer money, lost purely because of when it went in.

Without a True-Up

A $2,700 gap a year, compounded for a career.

If the plan does nothing to correct that shortfall — the ordinary case, called no true-up — the front-loader simply keeps less match every year, and never gets the missing dollars or the growth they would have earned. Run both savers for 20 years against real market returns, and the small annual gap compounds into a large one.

With a True-Up

Fix the match, and only timing is left.

Some plans add a year-end true-up: after the year closes, the employer pays whatever match you missed, so you end up with the full $5,400 no matter how you contributed. With the match made whole, the front-loader's shortfall vanishes — and the only difference left between the two savers is timing.

What We Found

Timing matters. What happens to your match matters more.

So, does the timing of your 401(k) contributions matter? Yes — but less than the folklore suggests. Contributing earlier genuinely helps, worth about 1% over 20 years when your match is protected. That is the pure timing effect, and it is modest.

The thing that so often travels with timing is far bigger. If your contribution pattern changes how much employer match you collect — as it does in any plan without a true-up — that can swing the outcome by a quarter-million dollars, swamping the timing effect entirely. So before you optimize the calendar, make sure every month earns its match, and find out whether your plan trues up. How that works, and what to do about it, is exactly what the true-up article is for.