Roth vs. Traditional: Pay the Tax Now or Pay It Later

Every retirement account with "Roth" in its name makes the same trade as its traditional twin, in the opposite order. A traditional 401(k) or IRA skips income tax on the money going in and taxes everything — contributions and growth — on the way out. A Roth account taxes the money going in and, once its rules are met, never taxes it again. Same account types, same investment menu, same growth. The only thing that differs is when the tax gets paid, and at what rate.

Two orders for the same tax

A traditional contribution comes out of your paycheck before income tax, so it lowers this year's taxable income. Decades later, every dollar withdrawn is taxed as ordinary income. A Roth contribution comes out of pay that has already been taxed, so it saves nothing this year — but qualified withdrawals (generally after age 59½ and once the account is at least five years old) come out tax-free, growth included. The IRS's Roth comparison chart lays out the side-by-side rules for 401(k)s and IRAs.

Neither one is an investment. Both are wrappers; the wrapper changes the tax, not the return.

The core math: multiplication doesn't care about order

Here's the part that most comparisons bury. Take $1,000 of salary and a 25% tax rate. The traditional route invests the full $1,000; at 7% a year for 30 years it grows about 7.6-fold to $7,612, and a 25% tax on the way out leaves $5,709. The Roth route pays the 25% first, invests the remaining $750, and the same 7.6-fold growth turns it into $5,709. To the dollar.

That's arithmetic, not coincidence: taxing then growing gives the same answer as growing then taxing, as long as the rate is the same at both ends. So "Roth or traditional?" is not a question about growth, compound interest, or which account is "better." It's one comparison: the tax rate on the money today versus the tax rate on the same money when it comes out.

A worked example on a real salary

The 401(k) match calculator runs this at full scale. Set the employer match rate to 0 so only your own money is counted, and use the page's other defaults: a $70,000 salary, 30 years, a 7% return, and 2% annual raises. For the tax rate, take 25% as an illustration of a combined federal and state marginal tax rate — not anyone's actual bracket.

Traditional at 6% puts $4,200 into the account in year one. Because that $4,200 skips a 25% tax, it only trims take-home pay by $3,150. A Roth contribution that costs the same $3,150 of take-home is 4.5% of salary. Run both:

• Traditional, 6%: $170,386 contributed over 30 years, $523,004 at the end — all of it still untaxed.
• Roth, 4.5%: $127,789 contributed, $392,253 at the end — none of it owed to anyone.

The traditional balance looks $130,751 bigger, and that is exactly the size of the tax bill inside it. Withdraw it all at 25% and $392,253 is left: a dead tie. Change only the rate at withdrawal and the tie breaks. At 15%, the traditional account nets $444,553 and comes out $52,300 ahead. At 35%, it nets $339,953 and the Roth is $52,300 ahead. Same paycheck cost, same investments, same 30 years — the entire gap is the difference between the rate at the start and the rate at the end. (One flat rate on the whole balance is a simplification; the next section covers what it hides.)

Marginal rate in, effective rate out

A traditional contribution saves tax at your marginal rate — the rate on the last dollars you earn, which are the dollars the contribution removes. Withdrawals in retirement work the other way up. They're stacked on top of whatever other income you have and taxed through the brackets from the bottom: some of the first dollars fall under the standard deduction, the next ones land in the lowest brackets. What the whole withdrawal pays ends up closer to an effective tax rate — the average across all of it — than to the top bracket it might touch.

That asymmetry is why traditional contributions often come out ahead for people whose retirement income ends up well below their working income, and it's the logic behind the standard textbook heuristic: Roth when your current rate is low (early career, a low-income year), traditional when it's high. The heuristic is just the rate comparison with a guess plugged in for the future.

The guess is the hard part. Tax brackets are set by law and change; you might move between a state with income tax and one without; Social Security benefits can become partly taxable once other income is high enough; and forced withdrawals (below) can push income up late in life. Nobody knows their tax rate thirty years out. That uncertainty is the case for holding some money on each side — what financial planners call tax diversification — so that each future year's withdrawals can be drawn from whichever bucket costs less that year.

When "same percentage" isn't the same deal

The tie above assumed equal take-home cost. Most people don't pick contributions that way; they pick a percentage. Contribute 6% to a Roth instead of 4.5% and the account ends at the same $523,004 as the traditional one — except every dollar of it is spendable, because the tax was paid along the way. That isn't free money: it cost $4,200 of take-home in year one instead of $3,150. It does mean a Roth dollar of contribution shelters more after-tax money than a traditional dollar, which matters for anyone contributing close to the annual limit. Those limits change every year, so the IRS retirement plans pages are the place to check the current figures.

The flip side: the equal-rate tie assumes the traditional saver's lower take-home cost is part of the plan. Someone who contributes 6% traditional and spends the $1,050 of tax savings has simply saved less than someone who put 6% into a Roth — the account type didn't cause the gap, the spending did.

The differences that aren't about rates

The employer match. Matching contributions have typically been deposited on the pre-tax side regardless of how you split your own money, so even an all-Roth saver usually ends up holding some traditional dollars. How match formulas work is covered in our 401(k) match article.

Forced withdrawals. Traditional accounts carry required minimum distributions: starting at an age set by law, the IRS requires a minimum amount out each year, taxed as income, whether you need it or not. Roth IRAs have no such requirement during the owner's lifetime, and Roth 401(k)s dropped theirs starting in 2024. The IRS's RMD page has the current starting age and the calculation.

Access before retirement. Contributions to a Roth IRA — not the earnings, just what was put in — can be withdrawn at any time without tax or penalty, because they were already taxed. Early withdrawals from traditional accounts are generally taxed and hit with a 10% additional tax. That's why some people count Roth IRA contributions as a last-resort backstop behind an emergency fund, though money pulled out can't be put back beyond the normal annual limit.

Who can contribute. Direct Roth IRA contributions phase out above income thresholds the IRS adjusts annually; the Roth option inside a 401(k) has no income cap. The IRS's traditional and Roth IRA page has the current thresholds.

Running your own numbers

The comparison takes two runs of the calculator: one at your traditional percentage, one at that percentage times (1 minus your marginal rate) for the Roth version that costs the same take-home. Multiply the traditional result by (1 minus a retirement tax rate) and compare. If the two numbers are close at the rates you believe, the choice matters less than the ads suggest; if they're far apart, the assumption about the future rate is doing all the work. The growth itself is the same either way, and compound interest, with real numbers is where that part lives.

Common questions

Can one person contribute to both?

Yes. Many 401(k) plans with a Roth option let you split a contribution percentage between the two sides, but the annual employee limit is shared across both, not doubled. The same goes for IRAs: one limit covers traditional and Roth IRA contributions combined.

Is Roth always better for young people?

Age isn't the variable; the rate is. Early-career income often sits in a lower bracket than later income, which is why the heuristic tilts young savers toward Roth. A high-earning 25-year-old and a 50-year-old in a low-income year face the same comparison with the numbers reversed.

What if tax rates go up?

Then money in a Roth has already paid the old rate, which is the bet a Roth makes. But what matters is your own rate at withdrawal, not tax rates in general. Rates could rise across the board while your retirement income sits in a lower bracket than your working income did.

Does the account type change how the money grows?

No. Both hold the same funds and earn the same returns. The traditional balance looks bigger only because part of it belongs to the tax bill; compare balances after tax, not before.

This article is general information, not personalized financial or tax advice. How we write and review articles is covered in the editorial note on our About page.