Roth 401(k) Calculator

Enter what you contribute, your tax rate now and the rate you expect in retirement, and this compares both accounts on the only number that matters: what you can actually spend after tax. It also handles the tax saving a traditional contribution hands you, which is where most comparisons go wrong.

Data reviewed: August 2026. Figures here come from published sources and change over time. How we verify

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The whole question is which tax rate you pay

Both accounts hold the same investments and grow at the same rate. The only difference is when the tax happens. A traditional 401(k) lets you skip income tax on the way in and charges it on the way out. A Roth charges you now and lets the money out untouched.

Which means the comparison is not really about investing at all. It is about a single question: would you rather pay tax at today's rate, or at whatever rate you will face in retirement? Every other consideration on this page is a footnote to that one.

The formula

Traditional: C × (1 + r)n × (1 − tlater)
Roth: C × (1 − tnow) × (1 + r)n

Where C is the contribution, r the return, n the years, and the two t values are your tax rates. Look at them side by side and something jumps out: they are the same three numbers multiplied together in a different order.

When your tax rate does not change, they tie exactly

Multiplication does not care what order you do it in. Taxing at the start then growing gives precisely the same answer as growing then taxing at the end, so long as the rate is the same both times.

This is not approximately true or true enough for planning purposes. It is exact, to the penny, at every contribution and every time horizon. If somebody tells you one account grows faster than the other, they are describing something else, because the growth is identical.

So the moment your two tax rates are the same, the tie is the answer, and the decision moves to things the arithmetic cannot settle: whether you would rather have certainty about the tax already being paid, or flexibility about when you pay it.

Worked example

A high earner at the limit. Contributing the 2026 maximum of $24,500, in the 35% bracket now, expecting 24% in retirement, over 30 years at 7%.

Traditional: $24,500 grows to $186,500.25. Tax at 24% takes it to $141,740.19. But the contribution also cut this year's tax bill by $8,575, and investing that in a taxable account leaves $56,770.07 after capital gains tax. Total: $198,510.26.

Roth: $24,500 grows to $186,500.25, and none of it is taxed.

Traditional wins by $12,010.01, which is what dropping eleven points of tax rate buys you.

Now change one number. Suppose retirement lands you in the same 35% bracket after all. The traditional side falls to $121,225.16 plus the same $56,770.07 side account, and the Roth now wins by $8,505.01.

Why the Roth wins at the same tax rate, and by exactly how much

That $8,505.01 is not a rounding artefact. It is exactly the capital gains tax paid on the side account, to the cent.

Here is what happened. If you are contributing the maximum, the traditional saver cannot put their tax saving into the 401(k), because the 401(k) is already full. It has to go somewhere else, and everywhere else is taxable. The Roth saver had no tax saving to place, because they paid the tax up front, but every dollar they did place is growing tax free.

So at the cap the accounts stop being equivalent, and the reason is that the limit is written in plain dollars. Twenty four thousand five hundred dollars of already-taxed money is worth more than twenty four thousand five hundred dollars that still owes tax, and the rulebook counts them the same. Filling a Roth shelters more real money than filling a traditional account.

This is the strongest argument for a Roth 401(k) for a high earner, and it is quietly the one least often made. It does not depend on guessing future tax rates at all.

The tax saving nobody invests

Everything above assumes the traditional saver takes their tax saving and invests it. That is the honest way to compare, because the Roth saver genuinely gave that money up.

It is also not what usually happens. The saving does not arrive as a cheque marked "invest me". It shows up as slightly more take-home pay across twenty six pay periods, and it gets spent, which is what money does when it turns up in a current account.

Switch the toggle above to spending it and watch the same example move: the traditional side drops to $121,225.16 against the Roth's $186,500.25, and the Roth is ahead by $65,275.09. That is a completely different answer to the same question, driven entirely by a behaviour rather than by any tax rule.

This is worth being honest with yourself about rather than aspirational. If you know the saving will be spent, the calculation that assumes otherwise is not describing you.

What this does not cover

Federal rates only. If you plan to retire somewhere with a different state income tax, add both state rates and run it again, because deferring in a high-tax state and withdrawing in a low-tax one is a real and legal saving.

Nor does it try to predict tax law thirty years out, and neither should anything else. The retirement rate you enter is a guess, and the sensitivity table shows how much the answer moves across a range of guesses, which is more useful than one confident number.

Two rules worth knowing that do not show up in the arithmetic. Roth balances in an employer plan no longer carry required minimum distributions, which changed in 2024, so the money can sit undisturbed. And your employer's match may land in the traditional side whatever you choose, unless your plan offers a Roth match and you elect it, in which case it counts as taxable income the year you receive it.

If you are 50 or older, the amount you are allowed to contribute changes, and for a high earner the catch-up may be required to be Roth regardless of preference. The 401(k) catch-up calculator covers those rules, and the Roth conversion calculator handles moving money that is already in a traditional account.

Frequently asked questions

Is a Roth or traditional 401(k) better for a high earner?

It depends almost entirely on your tax rate now against the rate you expect in retirement, and high earners often expect a lower one, which favours traditional. The exception is if you are already contributing the maximum, where the Roth quietly shelters more real money and can win even at the same tax rate.

What is the actual difference between them?

A traditional contribution skips tax now and pays it on the way out. A Roth contribution pays tax now and comes out untaxed. The money in between grows the same way in both, so the entire question is which tax rate you would rather pay: today's or the one you will face in retirement.

Why do they tie when my tax rate does not change?

Because multiplication does not care about order. Taxing at the start and growing, or growing and taxing at the end, land on the same number when the rate is the same. This is genuinely exact rather than approximately true, and it is why the tax rate comparison is the whole argument.

What is the tax saving that comparisons forget?

A traditional contribution reduces this year's tax bill, which hands you real money. A fair comparison has to invest that money, because the Roth saver had to give it up. If you spend it instead, the traditional account is no longer competing on equal terms, and the Roth pulls well ahead.

Why does the contribution limit favour the Roth?

Because the limit is a plain dollar figure, and the same figure means more in a Roth. Putting the maximum into a Roth shelters money that is already taxed, so all of it is yours later, while the same maximum in a traditional account still owes tax. At the cap, that difference is real money.

Do Roth 401(k)s have required minimum distributions?

Not any more. SECURE 2.0 removed RMDs from Roth accounts inside employer plans starting in 2024, which lines them up with Roth IRAs. Traditional 401(k) balances still carry them, which matters if you would rather leave the money alone.

Is the employer match Roth too?

It can be now, but it is not automatic. SECURE 2.0 allows employers to offer matching contributions as Roth, and if they do, that match counts as taxable income to you in the year it lands. Where the plan does not offer it, the match goes into the traditional side regardless of where your own money goes.

Can I split my contributions between both?

Almost always yes, and plenty of people do. The two share a single annual limit rather than getting one each, so splitting is about the mix rather than about contributing more. It is also the straightforward answer when you genuinely cannot tell which way your future tax rate goes.

Does moving to a state with no income tax change the answer?

It can, and it is a real consideration for anyone planning to retire somewhere cheaper. A traditional withdrawal is taxed by the state you live in when you take it, so deferring in a high-tax state and withdrawing in a no-tax one is a genuine saving. This calculator handles federal rates only, so add your state rates to both sides if that is your plan.

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