A Roth conversion calculator answers the one question that actually matters before you convert a traditional IRA or 401(k) to a Roth: is the tax bill you'll pay today smaller than the tax bill you'd otherwise pay decades from now? The tool above uses your current income and filing status to estimate what a conversion adds to this year's tax bill under 2025 brackets, then projects how that money grows tax-free versus how it would have been taxed on the way out of a traditional account.
Roth conversions get talked about constantly in retirement planning circles, but the decision is really a bet on your future tax rate versus your current one. Arb Digital built this calculator to make that bet visible in real numbers instead of vague rules of thumb, so you can decide with your CPA whether a conversion β full or partial β makes sense this year.
What This Roth Conversion Calculator Does
You enter the amount you're considering converting, your current taxable income, filing status, your expected tax rate in retirement, how many years until you'd withdraw the funds, and an expected annual investment return. The calculator adds the conversion amount on top of your current income and computes the additional federal tax using progressive 2025 brackets β that's the real cost of converting this year. It then projects how the converted balance grows completely tax-free inside the Roth versus how the same balance would grow inside a traditional account and get taxed at your expected retirement rate when withdrawn, so you can see the net benefit or cost of converting now.
How to Use It
- Enter the amount to convert. This can be a full account balance or a partial conversion β many people convert in smaller slices across several years to avoid jumping brackets.
- Enter your current taxable income for the year, before adding the conversion amount.
- Select your filing status so the calculator applies the correct 2025 bracket structure.
- Enter your expected tax rate in retirement. This is a judgment call β think about what bracket you expect to be in once Social Security, pensions, and required withdrawals are all factored in.
- Enter years until withdrawal and expected annual return to project long-term growth.
- Click Calculate to see the tax due now, your post-conversion bracket, projected future values, and the net benefit.
The Formula / How It's Calculated
A Roth conversion is treated by the IRS as ordinary taxable income in the year you convert β there's no special conversion tax rate. The calculator stacks the conversion amount on top of your existing taxable income and runs both figures through the 2025 progressive bracket schedule for your filing status, per IRS federal tax rate guidance. The difference between tax on (income + conversion) and tax on income alone is the marginal cost of converting. For the growth projection, the converted amount compounds at your expected return with zero future tax drag inside the Roth, while the same balance left in a traditional account compounds identically but gets taxed at your expected retirement rate the moment it's withdrawn. The net benefit compares the tax you'd avoid in the future against the tax you're paying today.
Why Low-Income Years Are the Best Time to Convert
The single biggest lever in this whole calculation is your current marginal bracket at the moment of conversion. A year with unusually low income β right after a layoff, during an early-retirement gap before Social Security and required minimum distributions begin, a sabbatical, or a year with large deductible business losses β can let you convert a meaningful chunk of a traditional account while staying in the 12% or 22% bracket instead of the 24% or 32% bracket you might otherwise be in during peak earning years. Many retirees deliberately convert in the years between stopping full-time work and reaching age 73, when required minimum distributions begin, because that window often has the lowest taxable income of their entire retirement.
Filling Up a Bracket Instead of Converting Everything
Very few people convert an entire large balance in a single year, because doing so often pushes a big chunk of the conversion into a much higher bracket than necessary. A common strategy is "bracket filling" β converting only enough each year to use up the remaining room in your current bracket before spilling into the next one. If you're sitting near the top of the 22% bracket with $15,000 of room left before hitting 24%, converting exactly that $15,000 this year and the rest over subsequent years usually beats converting the entire balance at once. This calculator's "bracket after converting" figure tells you immediately whether your proposed conversion amount is going to spill into a materially higher rate, which is the signal to consider splitting the conversion across multiple tax years.
Pay the Tax From Outside Funds
The math behind a Roth conversion only works in your favor if you pay the resulting tax bill from savings outside the retirement account β a checking account, brokerage account, or other cash on hand. If you pull money from the IRA itself to cover the tax (and you're under 59Β½), that withdrawal can trigger an additional 10% early withdrawal penalty on top of ordinary income tax, and it shrinks the amount actually working for you inside the tax-free Roth. Using outside funds lets 100% of the converted balance grow tax-free going forward, which is what makes the projected future value in the calculator above realistic.
Arb Digital builds fast, high-converting websites and content for financial planning practices. Explore more free calculators below.
Try the Estate Tax Calculator All Free ToolsCommon Mistakes to Avoid
- Converting a lump sum without checking bracket impact. A large one-time conversion can push income into much higher brackets than expected β spreading it out often costs less overall.
- Paying the tax from the IRA itself. This can trigger an early withdrawal penalty and shrinks the amount that grows tax-free.
- Ignoring Medicare IRMAA surcharges. A large conversion can spike modified adjusted gross income and trigger higher Medicare premiums two years later for those near or in retirement.
- Assuming your retirement tax rate will definitely be lower. Required minimum distributions, Social Security, and pensions can push retirement income higher than expected, which is exactly the scenario that makes conversions pay off.
- Forgetting state income tax. This calculator estimates federal tax only; states with income tax add another layer to the true cost of converting.
Related Free Tools From Arb Digital
If you're weighing a conversion as part of estate planning, the estate tax calculator shows how a smaller traditional balance affects a future taxable estate, and the gift tax calculator is useful if you plan to gift converted Roth funds to heirs later. Check the income tax calculator to see your full 2025 tax picture before converting, and the tax bracket calculator to find exactly how much room is left in your current bracket. Browse every calculator on our free online tools hub.
The Two Five-Year Rules Nobody Warns You About
A Roth conversion starts a clock, and there are actually two of them. The first is the conversion five-year rule: each conversion carries its own separate five-year waiting period before you can withdraw that converted principal penalty-free if you are under 59½. Convert in three different years and you are tracking three different clocks. Break one early and you owe a 10% penalty on the amount — not extra income tax, since you already paid that at conversion, but a penalty that erases much of the benefit.
The second is the account five-year rule, which governs whether your earnings come out tax-free. Your first Roth IRA contribution or conversion must be at least five tax years old, and you must be 59½ or older, before growth can be withdrawn tax-free. The clock starts on January 1 of the tax year of that first contribution, so a conversion made in December is credited with the whole year. That quirk is worth knowing: if you have never held a Roth, opening one with even a token amount today starts the clock years earlier than you might otherwise.
Pay the Tax From Outside the Account — Always
This is the single rule that separates a conversion that works from one that quietly fails. When the tax bill lands, you can either pay it from savings or have it withheld from the amount you are converting. Withholding it feels painless and is almost always the wrong move. Money withheld never reaches the Roth, so you shrink the tax-free account you just paid to create — and if you are under 59½, the IRS treats that withheld chunk as a distribution and adds a 10% penalty on top. Convert $100,000 and withhold the tax, and perhaps $76,000 actually lands in the Roth. Pay the same tax from a taxable brokerage account and the full $100,000 goes to work tax-free for the rest of your life. Run both versions through the calculator above and the gap over twenty years is rarely small.
The Hidden Cliffs a Conversion Can Trigger
A conversion is extra income for one year, and several thresholds react to that spike rather than to your normal earnings. IRMAA — the Medicare surcharge on Parts B and D — looks back two years, so a conversion at 63 can raise your premiums at 65, and it works on cliffs: one dollar over a threshold jumps the whole surcharge tier. If you buy health coverage through the ACA marketplace, extra income can shrink or wipe out your premium tax credit, sometimes costing more than the conversion tax itself. A spike can also drag more of your Social Security into taxable territory and push long-term capital gains from the 0% band into 15%.
All of which points to the same conclusion: timing beats size. The best window for most people is the gap years — after you stop working but before Social Security and required minimum distributions begin — when taxable income is unusually low. Convert just enough each year to fill your current bracket without spilling into the next, repeat annually, and you move a large balance to tax-free status at a fraction of the rate a single big conversion would cost. Use the calculator above once per year with that year's real numbers rather than planning it all at once.
Frequently Asked Questions
Yes. The converted amount is added to your taxable income for the year and taxed at your ordinary marginal tax rates β there is no special conversion tax rate.
Generally in years when your taxable income is unusually low, such as early retirement before Social Security or required minimum distributions begin, so the conversion is taxed at a lower bracket.
It's usually better not to. Paying tax from outside savings keeps the full converted balance growing tax-free and avoids a possible early withdrawal penalty if you're under 59Β½.
Yes, partial conversions are common and often smarter than converting the full balance at once, since they let you stay within a target tax bracket each year.
It can. A large conversion raises your modified adjusted gross income, which may trigger higher Medicare Part B and Part D premiums (IRMAA) two years later.
No, it's an illustrative estimate using 2025 federal brackets. It doesn't include state income tax, credits, or every deduction, so confirm exact figures with a tax professional.
This tool provides general estimates for educational purposes only and is not financial, tax, legal, or medical advice. Figures are illustrative; consult a licensed professional for decisions.
