How much should I convert?

A common answer is the amount that exactly fills your current bracket, which is the highlighted row in the table. It converts as much as possible at the rate you are already paying and stops before the higher one starts. Converting past it is not automatically wrong — it just needs the higher blended rate to still beat what you expect to pay on that money later.

How is a conversion taxed?

The full amount converted is added to your ordinary income for the year and taxed at your marginal rates, so it stacks on top of whatever income you already have. There is no separate conversion tax and no preferential rate. This calculator prices it as the difference between your federal tax with the conversion and without it.

Should I pay the tax out of the converted money?

Preferably not. Withholding the tax from the conversion means less money lands in the Roth, which cancels much of the reason to convert at all. Before age 59½ the withheld portion is treated as a distribution rather than a conversion and can attract an early-withdrawal penalty on top. Paying from a taxable account keeps the whole balance working.

Is there a limit on how much I can convert?

No. Conversions have no dollar cap and no income limit, unlike Roth contributions. The practical limit is the tax bill: the more you convert in one year, the higher the bracket the last dollars land in, which is what the comparison table is showing you.

When does a conversion make the most sense?

In a year when your marginal rate is unusually low — an early-retirement gap year before Social Security and required distributions begin, a year out of work, or a business loss year. It also makes sense if you expect rates to rise, or if the money is destined for heirs who will be in a higher bracket than you are.

What does this calculator leave out?

State income tax, Medicare premium surcharges that a high-income year can trigger, the extra Social Security that becomes taxable as your income rises, and the five-year clock that applies to each converted amount before it can be withdrawn penalty-free. Any of those can make a conversion more expensive than the federal number here.

Roth Conversion Calculator — Bracket Headroom

Conversion sizes compared

The same conversion at several sizes. The highlighted row is the amount that exactly fills your current bracket.

Federal tax on a Roth conversion at $85,000 of other ordinary income, by amount converted.
Converted	Federal tax	Effective rate	Rate after
$25,000	$3,000	12.0%	12%
$48,000	$5,760	12.0%	22%
$50,000	$6,200	12.4%	22%
$100,000	$17,200	17.2%	22%
$200,000	$40,028	20.0%	24%

Federal ordinary income tax only, for this year alone. The effective rate is the tax divided by the amount converted; the rate after is the marginal rate you sit at once the conversion has landed.

Bracket headroom is the number the decision turns on: how much more ordinary income you can take before the next federal rate starts applying.
A large conversion is taxed at a blend of rates, not at the top rate it reaches. Compare the effective rate, not the marginal one, against the rate you expect to pay later.
Pay the tax from outside the account if you can. Withholding it from the conversion shrinks the amount that reaches the Roth, and before age 59½ the withheld part can itself be penalised.
A conversion cannot be undone. Recharacterizing one is no longer permitted, so the amount is a one-shot decision each year — which is an argument for converting in several smaller annual steps.

How the Roth conversion calculator works

A Roth conversion moves money you already have from a traditional IRA or 401(k) into a Roth. It is not a contribution, so contribution limits and income limits do not apply to it. What does apply is tax: the amount you convert is added to this year’s ordinary income and taxed accordingly. In exchange, that money never gets taxed again, and inside a Roth IRA it stops being subject to lifetime required minimum distributions.

The decision turns on one figure that this page puts in the input panel and nowhere else on the site shows: bracket headroom. Federal brackets are marginal, so a conversion is never taxed at a single rate. It fills whatever is left of your current bracket at that rate, then spills into the next one. “Convert up to this amount and stay in your current bracket” is the sentence most real conversion decisions come down to, and a calculator that only prices one amount cannot tell you where that line is.

So the table compares several conversion sizes side by side rather than one, with the amount that exactly fills your bracket highlighted. For each size it shows the federal tax, the effective rate — the tax as a share of the amount converted — and the marginal rate you land on afterwards. The effective rate is the figure to compare against the rate you expect this money to be taxed at if you leave it where it is.

The math

The tax is computed incrementally, not as an average. The calculator works out your federal ordinary income tax with the conversion and without it, and reports the difference. That is the only honest way to price one: its cost depends entirely on where your existing income has already put you, so the same conversion is cheap for someone sitting low in a bracket and expensive for someone already near the top of one.

Bracket position is computed on taxable income — the income you enter, less the standard deduction for your filing status — and headroom is the distance from there to the top of the bracket you are in. Because the deduction is a fixed subtraction, one dollar of headroom is one dollar of conversion. If you are already in the top bracket the panel says so, since there is no next rate to cross. The rate-after figure is your marginal rate once the conversion has landed, so when it reads higher than the rate before, the conversion crossed a line.

What is not modelled matters as much as what is. This is federal ordinary income tax only: no state income tax, no Medicare premium surcharges triggered by a higher income year, no change to how much of your Social Security becomes taxable, and no interaction with the preferential rate on your capital gains. It also assumes you pay the tax from outside the account, and it prices this year alone — a multi-year plan is a sequence of these, each with its own headroom.

Worked example

On the defaults — $85,000 of ordinary income, married filing jointly — the standard deduction leaves $52,800 of taxable income, which sits in the 12% bracket with $48,000 of headroom before 22% begins. Converting the default $50,000 costs $6,200 in federal tax, an effective rate of 12.4%. The split is the whole story: the first $48,000 was taxed at 12 cents on the dollar and the last $2,000 at 22, which is why the effective rate is not a round 12%.

The table makes the shape visible. Converting exactly $48,000 costs $5,760, a flat 12%, and leaves you at the very top of the bracket. Converting $100,000 costs $17,200, an effective 17.2%. Converting $200,000 costs $40,028, an effective 20.0%, even though the last dollars of it are taxed at 24%. That gap between the effective rate and the top marginal rate a conversion reaches is what people miss when they say a large conversion is “taxed at 24%”. It is taxed at a blend.

Key terms

Roth conversion: Moving money from a traditional IRA or 401(k) into a Roth account. The amount converted is added to your ordinary income for the year and taxed at your marginal rates.
Bracket headroom: Additional ordinary income you can take before the next federal marginal rate applies. Measured on taxable income, after the standard deduction.
Effective rate: The tax caused by the conversion divided by the amount converted. Always lower than the top marginal rate the conversion reaches, because the earlier dollars are taxed less.
Marginal rate: The rate on your next dollar of ordinary income. The rate before and the rate after tell you whether the conversion pushed you into a new bracket.

Roth Conversion Calculator (US, 2026)