401(k) Contribution Calculator

How much each paycheck puts in, how much room is left under the limit, and which election reaches it without giving up any of the employer match — for one or two earners paid every two weeks, with separate paycheck and bonus elections and both pre-tax and Roth.

When the match is paid matters

Two plans can advertise the same match and pay very different amounts for the same total contribution. The difference is when the match is calculated.

Per-paycheck, no true-up

Each check is matched on what that check put in
Payroll stops deducting once you reach the annual limit
A check that contributes nothing is matched on nothing
Front-load too hard and December's match is simply gone

Year-end true-up

The match is recomputed on the whole year's pay and contributions
When the money went in does not matter
Whatever is owed arrives as a deposit the following year
Front-loading costs nothing

Say a $130,000 salary pays $5,000 a check and the plan matches dollar for dollar up to 5% of pay, per paycheck. At 20% a paycheck, $1,000 a check, the limit is reached on the 25th check of 26, and the 26th contributes nothing: $250 of match, lost. At 19% the limit is reached on the last check instead, and nothing is lost.

One point of election makes the difference — and your summary plan description, or HR, is what tells you which kind of plan you are in.

Tiered matches

Plenty of plans match in bands rather than at one rate: 100% of the first 2% of pay, then 50% of the next 3%, say. Enter each band as a tier, in the order the plan document lists them. That formula pays 3.5% of pay in match, but only if you put in the full 5% — at 4% the second band is only two-thirds used. The calculator works out that threshold for you and treats anything below it as match left on the table.

The last paycheck is matched on what it puts in

The check that reaches the limit usually contributes only what is left of it, which can be a few dollars. If that is less than the percentage the full match needs, the match on that check is smaller too. Most rough calculations treat that check as fully matched. This one does not, which is why it sometimes recommends a point lower than a quick division would.

Paycheck and bonus elections

Many plans let you elect a different percentage on a bonus check. A bonus uses up the limit on the day it is paid, not evenly across the year — so a large bonus deferral in March can bring the limit forward and, on a per-paycheck plan, cost match at the end of the year. The calculator runs every paycheck and the bonus in date order to catch exactly that.

It checks every whole-percent combination of paycheck and bonus election and shows the one that gives up the least match, then contributes the most, then keeps the bonus election as low as it can. Where there is room left, it also shows the other common approach: keep the paycheck election you have and use the bonus election to fill the rest.

Pre-tax or Roth

Both count toward the same annual limit, and employers generally match both. The difference is when you pay tax. Pre-tax contributions come off this year's taxable income, so the calculator estimates the federal income tax they avoid at your marginal rate. Roth contributions are taxed now and come out tax-free in retirement, so they save nothing this year. Which is better depends on your tax rate now against what you expect later, and is worth a conversation rather than a default.

Neither kind avoids Social Security or Medicare tax — unlike an HSA contribution through payroll, which does. And state treatment varies: most states follow the federal rule, but Pennsylvania taxes 401(k) contributions anyway, which is why only federal savings are shown.

Catch-up contributions

From the year you turn 50 you can contribute an extra amount on top of the limit, and a higher amount in the years you turn 60 through 63. Set the age for each earner and the calculator raises the limit to match.

Starting in 2026, catch-up contributions for people whose wages the year before were above an income threshold have to go in as Roth. Check with your plan before counting on a pre-tax catch-up.

If the year has rolled over

The limits change most years, announced by the IRS each fall. If they have moved and this page has not caught up, open Contribution limits under the calculator and type in the new figures — everything recalculates. When you plan next year on this year's figures, the page says so rather than quietly using them.

What this doesn't do

It assumes elections in whole percentages, a salary that holds steady for the year, and a paycheck that is a twenty-sixth of it. It does not cover after-tax contributions beyond Roth, the separate limit on total employer and employee additions, vesting, or a plan that stops matching partway through the year.

And it answers how to put money in, not how much you should. Reaching the limit is one option among several, and collecting the full match is usually the first; where the rest of your money goes is the kind of question we work through in sessions.