Roth Conversion Calculator
A Roth conversion means paying income tax now to move pre-tax retirement money into a tax-free Roth. It wins when your future tax rate is the same or higher. This calculator compares the after-tax value of converting versus leaving the money, so you can see which comes out ahead.
Use this Roth conversion calculator to decide whether to convert a traditional IRA to a Roth. Enter the amount, your current and expected retirement tax rates, the years until you withdraw and your expected return — and it compares the after-tax value of each path and names the winner.
Enter the amount, tax rates, horizon and return, then press Calculate.
How the Roth conversion calculator works
The decision comes down to one question: is your tax rate higher now or later? To answer it fairly, the calculator follows the same dollars down both paths. If you convert, you pay tax at today's rate on the amount, and what is left grows tax-free in the Roth, so nothing is owed at withdrawal. If you don't convert, the whole amount keeps growing in the traditional account, but every dollar is taxed at your retirement rate when you take it out.
Comparing the two after-tax totals shows the winner and the size of the edge. The result hinges on the gap between your current and future tax rates — convert when the future rate is as high or higher. Pair this with the Roth IRA calculator to project tax-free growth, and the RMD calculator to see the future distributions a conversion can reduce.
The comparison
- rate now — tax paid on conversion
- rate later — tax on traditional withdrawal
- Convert wins — when rate later ≥ rate now
It is really a bet on tax rates
Strip away the mechanics and a Roth conversion is a wager that your tax rate will not be lower in the future. When you convert, you swap an unknown future rate for today's known one. That is why low-income years are the sweet spot — an early-retirement gap before Social Security and RMDs begin, a sabbatical, or a market dip that temporarily shrinks the balance. If you are confident your rate will fall sharply in retirement, converting can cost you; if you expect it to hold or rise, converting locks in the cheaper tax.
Watch the ripple effects
The tax on the conversion is only the headline cost. A large conversion adds to your income for the year, which can push part of it into a higher bracket, increase how much of your Social Security is taxed, and raise your Medicare premiums two years down the line. That is why many people convert gradually — enough to "fill up" a tax bracket each year without spilling into the next. Model a few different amounts here, and consider paying the tax from outside funds so the whole balance keeps its Roth advantage.
The 5-year rule and Roth conversion ladders
Each Roth conversion starts its own five-year clock. If you are under 59½, you must wait five years before withdrawing the converted amount penalty-free, and every conversion has a separate clock. Smart early retirees turn this into a conversion ladder: they convert a set amount from a traditional IRA to a Roth each year, and five years later each tranche becomes available penalty-free. Repeat it annually and you build a rolling stream of accessible money — a popular way to fund the years before 59½ in a FIRE plan while paying tax at a low rate. It takes planning and at least five years of lead time, so the ladder is best started early.
Estimate only — not tax or investment advice. Uses flat marginal rates and ignores bracket effects, Medicare and Social Security impacts. Confirm with a tax professional before converting.
How to use it & key terms
Enter the amount to convert, your current and retirement tax rates, the years to withdrawal and expected return, then press Calculate to compare the two paths.
| Term | What it means |
|---|---|
| Roth conversion | Moving pre-tax money into a Roth and paying tax now. |
| Marginal tax rate | The rate on your next dollar of income. |
| After-tax value | What you keep after all tax is paid. |
| Backdoor Roth | A conversion used by high earners above the Roth income limit. |
| Bracket filling | Converting just enough to stay within a tax bracket. |
| Break-even | The point where converting and not converting are equal. |
Sources & methodology
The calculator compares two after-tax outcomes for the same starting amount. In the conversion case, tax is charged at your current marginal rate, and the remaining amount grows at the expected return for the number of years, then is withdrawn tax-free — giving amount × (1 − current rate) × (1 + return)^years. In the no-conversion case, the full amount grows for the same period and is taxed at your retirement marginal rate on withdrawal — giving amount × (1 + return)^years × (1 − retirement rate). The path with the higher after-tax value wins. The model conservatively assumes the conversion tax is paid from the converted amount; paying it from outside funds improves the Roth result. It uses flat marginal rates and does not model tax brackets, Medicare or Social Security effects.
Sources: Standard after-tax future-value comparison for Roth conversions. Uses the tax rates you enter.
Converting with heirs in mind
Most conversion decisions weigh your own future tax rate against today's, but a Roth can also be one of the most tax-efficient things you leave behind — and that changes the maths. When you convert, you prepay the income tax that would otherwise have followed the money out of a traditional account. Pass a Roth to your heirs instead, and they inherit a pot with the tax already settled: withdrawals come out tax-free for them, at a time in their lives when they may well be in their own peak earning years and highest brackets. In effect, paying the tax now at your rate can spare them from paying it later at theirs.
Under current rules, most non-spouse heirs must empty an inherited retirement account within about a decade. For an inherited traditional account, that means a wave of taxable withdrawals landing on top of the heir's existing income, potentially at an unwelcome moment. An inherited Roth still has to be emptied on a similar timetable, but because those withdrawals are tax-free, the squeeze largely disappears — and the money can keep growing tax-free inside the inherited account until it comes out.
There is a nearer-term reason couples consider converting together, too. When one spouse dies, the survivor often shifts to a single filer's tax treatment, where the same income can be taxed more heavily. Converting while both spouses are alive — and both sets of brackets are available — can head off part of that future squeeze, and it leaves the survivor with a tax-free source of income at a time when their filing status has turned less forgiving.
A Roth's lack of lifetime required withdrawals reinforces all of this. Because the original owner is never forced to draw the account down, it can be left to compound untouched and handed on close to intact, rather than being whittled away by mandatory distributions. That makes conversions as much an estate-planning tool as a personal tax play. The calculator above compares the after-tax outcomes for you; if leaving money to family is part of your plan, it is worth weighing your heirs' likely tax rates alongside your own, and remembering that a Roth removes the required withdrawals a traditional account would otherwise face.
Frequently asked questions
What is a Roth conversion?
A Roth conversion moves money from a pre-tax account, such as a traditional IRA or 401(k), into a Roth IRA. You pay ordinary income tax on the amount converted in the year you do it, and in exchange the money then grows tax-free and comes out tax-free in retirement. It is a way to prepay tax at today's rate to escape tax on all future growth, and to remove future required minimum distributions.
When does a Roth conversion make sense?
A conversion tends to pay off when you expect your tax rate in retirement to be the same as or higher than it is now, because you lock in the lower rate on the amount converted. Low-income years — early retirement before Social Security and RMDs, a gap between jobs, or a market dip — are classic windows. It makes less sense if you expect a much lower rate later, or if you would have to pay the conversion tax from the IRA itself.
How is the tax on a Roth conversion calculated?
The amount you convert is added to your taxable income for the year and taxed at your marginal rate. Converting $100,000 at a 22% marginal rate costs about $22,000 in tax. Large conversions can push part of the amount into a higher bracket, so many people convert in stages to fill up a bracket without spilling into the next. This calculator uses the marginal rate you enter to estimate the tax and compare outcomes.
Should I pay the conversion tax from the IRA or from other money?
Paying the tax from outside savings is almost always better, because it lets the full converted amount keep growing tax-free in the Roth, and it avoids a possible early-withdrawal penalty on the money used to pay the tax. Paying the tax out of the IRA shrinks the amount that gets the Roth's tax-free treatment. This calculator conservatively assumes the tax is covered from the conversion, so paying it from outside funds would improve the Roth outcome further.
What is a backdoor Roth?
A backdoor Roth is a strategy for high earners who are above the income limit to contribute to a Roth IRA directly. They contribute to a traditional IRA — which has no income limit for non-deductible contributions — and then convert it to a Roth shortly after. The conversion has no income ceiling. The pro-rata rule can make it taxable if you hold other pre-tax IRA money, so it is worth understanding the mechanics or getting advice first.
What are the risks of a Roth conversion?
The main risk is paying tax now that you did not need to — if your retirement rate turns out lower, you would have been better off leaving the money. A large conversion can also bump you into a higher bracket, raise Medicare premiums two years later, or make more of your Social Security taxable. Conversions are also irreversible. Because the outcome depends on future tax rates you cannot know for sure, it is a decision to model carefully and often to spread over several years.
What is the pro-rata rule for Roth conversions?
The pro-rata rule stops you from converting only your after-tax IRA dollars while leaving the pre-tax money behind. The IRS treats all your traditional, SEP and SIMPLE IRAs as one pool, so each conversion is taxed in proportion to how much of that whole pool is pre-tax versus after-tax. For example, if 90% of your total IRA money is pre-tax, then 90% of any conversion is taxable, even if you meant to convert only non-deductible contributions. This is the main reason a backdoor Roth can trigger an unexpected tax bill.
When is the best time to do a Roth conversion?
Conversions work best in your lower-income years, when the tax you pay to convert is cheaper. Classic windows include the gap years after you retire but before RMDs and Social Security begin, a year with unusually low income, or a market dip that lets you convert a temporarily depressed balance. A common approach is to convert just enough each year to fill up your current tax bracket without spilling into the next one. Converting before RMD age can also shrink future required withdrawals and their tax.