Tool · Money
Put the same pre-tax dollars through a Roth account and a Traditional one, and the calculator shows what each leaves you after tax in retirement — and the retirement tax rate at which the two come out even.
Where does each number come from?
- Pre-tax dollars to put away
- One year’s contribution, before any tax comes out. Running the same pre-tax amount through both accounts is the fair comparison, and it assumes that if you go Traditional you put the tax you didn’t pay into the account too. If you’d rather compare the same after-tax amount, it’s the same math with the Traditional side reduced by the tax owed on it.
- Your tax rate now
- Your marginal rate — the rate on your next dollar of income, not the rate on all of it. It’s the bracket your taxable income lands in on the IRS’s 2026 table, and the money glossary walks through finding it from your last return.
- Your tax rate in retirement
- A guess, and the calculator says so. Nobody knows their bracket thirty years out; what you can do is run it twice, once low and once high, and watch which way the answer tips.
- Years until you take the money out, and yearly growth
- These multiply both sides by the same amount, so they change the dollar figures without changing which side wins. The growth box starts at the ten-year Treasury yield, a published rate with a date on it.
What moves the answer?
Only the two tax rates decide the winner. Let’s say you put $5,000 pre-tax into each account, at 22% today, and it grows for thirty years at 5%. If your rate in retirement is also 22%, the two accounts leave you exactly the same amount — about $16,900 each. If your rate in retirement drops to 12%, Traditional leaves you about $19,000, around $2,100 more, because you paid the lower rate. If it rises above 22%, Roth wins by the same logic in reverse.
The comparison comes down to one thing: pay the tax now at today’s rate, or later at that year’s rate. The even point the calculator reports is the rate where those two are equal — which is always your rate today.
What does the calculator take as given?
- The 2026 tax brackets
- Come from the IRS’s Revenue Procedure 2025-32, released 9 October 2025.
- The contribution limits
- For 2026 you can put $7,500 into IRAs across both kinds, plus $1,100 more if you’re 50 or over, and $24,500 of your own pay into a 401(k), from IRS Notice 2025-67 of 13 November 2025. The calculator warns you above a limit and doesn’t stop you typing it.
- Who can use a Roth IRA
- The IRS phases the Roth IRA out between $153,000 and $168,000 of modified income for single filers and between $242,000 and $252,000 filing jointly. A Roth 401(k) has no income limit. The calculator warns above the IRA limit.
- Who gets the Traditional deduction
- If a workplace plan covers you, the deduction for a Traditional IRA phases out between $81,000 and $91,000 single and $129,000 and $149,000 joint. Every one of these figures sits in The Money Numbers with its quote and date.
- The growth rate
- Starts at 5.01%, the ten-year Treasury yield on 18 September 2026 from the Federal Reserve’s daily release. A government bond rate, and not a forecast of anything.
- What's left out
- State income tax. Required withdrawals from a Traditional account after a certain age. How Social Security gets taxed. Employer matching. And the fact that a real retirement withdrawal is taxed bracket by bracket, not at one flat rate — the calculator uses one rate at each end so you can see the mechanism.
The five thousand dollars and the twenty-two percent are one made-up saver; your own bracket is on last year's return, your plan's rules are in its summary document, and your rate in retirement is the one number here nobody can look up.
Sources
- Internal Revenue Service, Revenue Procedure 2025-32 — tax year 2026 brackets (released 9 October 2025, IR-2025-103).
- Internal Revenue Service, Notice 2025-67 — 2026 IRA and 401(k) limits, catch-ups and income phase-outs (released 13 November 2025, IR-2025-111).
- Federal Reserve, Statistical Release H.15 — 10-year Treasury constant maturity, 5.01% on 18 September 2026, release of 21 September 2026.
- Bills & Beans, The Money Numbers That Change Every January — every figure above with its quote and date.