401(k) & Roth IRA Calculator

The tool runs two savers side by side. One puts money into a traditional 401(k) before tax and pays tax on every dollar taken out later. The other uses a Roth account: tax is paid now, and qualified withdrawals come out tax free.

To be fair, both paths cost the same take-home pay. A pre-tax contribution $C$ lowers your tax bill, so it only shrinks your paycheck by $C\,(1 - t_{\text{now}})$. That smaller amount is what goes into the Roth. At a 22% rate, $8,000 pre-tax costs $6,240 of take-home pay, so the Roth gets $6,240.

Each path grows with deposits at the end of each year:

• $B$ is what you have saved already.
• $P$ is the yearly deposit: your contribution plus any employer match.
• $r$ is the yearly return and $n$ the years to retirement.

At retirement, pre-tax money loses your retirement rate $t_{\text{later}}$ to tax; Roth money keeps it all. The match always lands in a pre-tax account, so it is taxed later on both paths. A Roth IRA gets no match at all, because only the workplace plan pays one.

The break-even rate is the retirement rate at which both paths end level. The growth factor appears on both sides and cancels, so years and return drop out:

Here $M$ is the yearly match on each path. With the same match on both, the break-even is simply your tax rate today.

Dana, mid-career in the 22% bracket

Dana is 35, earns $80,000 and puts $8,000 a year into her 401(k). Her employer matches 100% up to 6% of pay, which is $4,800 a year. She has $50,000 saved pre-tax and $20,000 in a Roth, and expects 7% a year until 65.

If her rate falls to 18% in retirement, the traditional path leaves $1,455,808 after tax and the Roth 401(k) leaves $1,425,581. Traditional is $30,227 ahead, or $12,453 at today's prices with 3% inflation. If her rate is 24% instead, the Roth wins by $15,114. Open this example in the tool

Leo, first job in the 12% bracket

Leo is 25, earns $55,000 and defers 6% of pay, $3,300 a year. His plan matches 50% up to 6%. He pays 12% tax now and expects 22% later, once his pay has grown.

The Roth 401(k) leaves $805,839 at 65 against $770,791 for traditional, $35,048 more. Note the break-even is 16.98%, not 12%. At the same take-home cost his Roth deferral is $2,904, which earns $1,452 of match instead of $1,650. Open this example in the tool

Priya, tempted to skip the match

Priya, 30, earns $70,000. Her employer matches 100% up to 4% of pay, so a $2,800 deferral brings in $2,800 of free money. She wonders about putting the same take-home cost, $2,184, into a Roth IRA instead.

At 22% now and later, the 401(k) with the match leaves $603,819. The Roth IRA leaves $301,909, about half. The break-even jumps to 61%, a rate no one pays. A Roth 401(k) keeps part of the match and ends at $537,399. Open this example in the tool

The big number is how much more one path leaves to spend at retirement. Switch it to today's dollars to see it at current prices. Over 30 years at 3% inflation, a future dollar buys about 41 cents of today's goods.

The tax rates decide the winner; the return and the years only scale the gap. If you expect a lower rate in retirement than now, traditional usually wins. If you expect a higher one, Roth usually wins. For 2026, the federal rates are 10%, 12%, 22%, 24%, 32%, 35% and 37% (IRS Rev. Proc. 2025-32). Use the top rate that applies to your last dollars of income, plus any state rate.

Check your contribution against the 2026 limits from IRS news release IR-2025-111. They apply to tax year 2026; the IRS usually sets the next year's figures each November.

Direct Roth IRA contributions phase out between $153,000 and $168,000 of modified AGI for single filers, and between $242,000 and $252,000 for married couples filing jointly. A Roth 401(k) has no income limit. If your 2025 Social Security wages from your employer were over $150,000, any catch-up contribution has to go in as Roth (IRS, catch-up contributions).

• Comparing the same dollar amount. $8,000 in a Roth costs more take-home pay than $8,000 pre-tax. Compare equal paycheck cost, as this tool does, or the Roth looks better than it is.
• Leaving the match on the table. As Priya's example shows, a match is an instant 50% or 100% return. Contribute enough to get all of it before you add a Roth IRA.
• Using your top rate for retirement. Withdrawals fill the brackets from the bottom, so your average rate on them is often lower than your top rate today. Use the rate you expect on the money you take out.
• Forgetting the Roth rules. Earnings come out tax free only after age 59½ and five years in the account (IRS, designated Roth accounts). Traditional accounts also have required minimum distributions; Roth 401(k) accounts no longer do from 2024.
• Ignoring state tax. Moving from a state with income tax to one without can flip the answer. Add the state rate to both tax fields.