Roth Conversion Calculator 2026: How Much to Convert Each Year to Minimize Taxes
A Roth conversion can reduce future required minimum distributions and create a pool of potentially tax-free retirement income. The tradeoff is immediate: the taxable portion of the conversion is generally added to your ordinary income for the year.
A useful Roth conversion calculator for 2026 should therefore answer more than “How much tax will I owe?” It should identify how much you can convert within a chosen tax bracket, show the effect of spreading conversions across several years, and warn you when additional income may affect Medicare premiums, Social Security taxation, or income-based deductions.
The calculations below are estimates for planning purposes. Tax law interactions are complex, and the lowest current-year tax bill is not necessarily the best lifetime strategy. Confirm any final conversion with a qualified tax professional.
What a Roth Conversion Calculator Should Tell You
At a minimum, a 2026 Roth conversion calculator should provide five results:
- Incremental federal tax: The difference between estimated federal income tax with and without the conversion.
- Remaining bracket capacity: How much additional taxable income can fit below the top of the federal bracket you are willing to pay.
- Multi-year comparison: The estimated cost of converting a large amount now versus dividing it among several tax years.
- Secondary tax effects: Potential changes to Medicare income-related monthly adjustment amounts, taxable Social Security, deductions, credits, and capital-gains taxation.
- Future retirement impact: An estimate of how converting now could reduce later traditional-account balances and required minimum distributions.
The output should not be presented as a guaranteed “optimal” answer. Future tax rates, investment returns, income, residency, filing status, and spending needs can all change.
Inputs to Gather Before Calculating Your 2026 Conversion
The quality of the result depends on the quality of the income projection. Gather the following information before entering a conversion amount:
- Filing status, such as single, married filing jointly, head of household, or married filing separately
- Projected 2026 taxable income before the conversion
- Wages, pensions, business or K-1 income, interest, dividends, capital gains, rental income, and retirement withdrawals
- Social Security benefits and the estimated taxable portion
- Traditional IRA, SEP IRA, SIMPLE IRA, 401(k), 403(b), and existing Roth balances
- After-tax basis reported on prior Forms 8606
- Age, Medicare enrollment, anticipated required minimum distribution age, and state of residence
- Expected standard or itemized deductions and any income-based deductions or credits
- Cash or taxable assets available to pay the conversion tax
Do not confuse gross income, adjusted gross income, modified adjusted gross income, and taxable income. Federal tax brackets apply to taxable income, while Medicare IRMAA and several deductions use versions of modified adjusted gross income. A calculator that treats these figures as interchangeable can produce a misleading recommendation.
The Core Formula: Calculate Your Conversion Room
The basic bracket-filling formula is straightforward:
Preliminary conversion amount = upper taxable-income threshold of the target bracket − projected taxable income before conversion
For example, if projected taxable income is $150,000 and the applicable bracket ends at $201,775, preliminary conversion room is:
$201,775 − $150,000 = $51,775
This formula is only the starting point. A more complete process is:
- Project taxable income without a conversion.
- Select the highest marginal federal rate you are willing to pay.
- Subtract projected taxable income from that bracket’s upper threshold.
- Recalculate Social Security taxation, deductions, credits, capital-gains rates, and net investment income tax exposure.
- Check Medicare IRMAA thresholds if either spouse is or soon will be enrolled in Medicare.
- Add state income tax and account for any state-specific retirement exclusions.
- Compare the current marginal cost with the rate likely to apply to future withdrawals or beneficiaries.
The final amount may be lower than the preliminary bracket room if an additional dollar of income triggers another cost. It may also be reasonable to cross a threshold deliberately when the long-term benefit of the conversion is expected to outweigh that cost.
How Much Should You Convert in 2026?
Single-filer example: $51,775 of conversion room
Assume a single taxpayer expects $150,000 of taxable income before converting. Using a 2026 upper threshold of $201,775 for the 24% bracket, the taxpayer could convert as much as $51,775 without entering the next federal bracket.
| Calculation | Amount |
|---|---|
| Taxable income before conversion | $150,000 |
| Top of selected bracket | $201,775 |
| Preliminary conversion room | $51,775 |
| Estimated federal tax on conversion at 24% | $12,426 |
Because all $51,775 falls within the 24% bracket in this simplified example, its marginal federal cost is 24%. The taxpayer’s overall effective rate remains lower because earlier layers of taxable income are taxed at 10%, 12%, and 22%.
This distinction matters. Multiplying the entire year’s income by the highest marginal rate overstates federal tax. The calculator should instead calculate tax under the progressive brackets twice—once without the conversion and once with it—and report the difference.
Married-couple example: approximately $133,000 of lower-bracket capacity
For a married couple filing jointly with no other income, roughly $133,000 of gross ordinary income could fall within the standard deduction and the 10% and 12% brackets, assuming a 2026 standard deduction of approximately $32,200 and a 12% taxable-income ceiling of approximately $100,800.
That does not mean every couple should convert $133,000. Social Security, pensions, dividends, realized gains, IRA withdrawals, and business income use part of that capacity. The couple must begin with projected taxable income after deductions, not with retirement-account value alone.
Why converting an entire IRA may be expensive
Roth conversions have no income eligibility limit and no annual dollar cap. A taxpayer can convert part or all of an eligible account. However, a large conversion is stacked on top of other income and may push successive portions into the 32%, 35%, or 37% brackets.
The absence of a legal conversion cap should not be mistaken for a recommendation to convert everything. The practical constraints are the tax bill, related income thresholds, available cash, and whether the current rate is favorable compared with expected future rates.
Multi-Year Roth Conversion Scenarios
One $300,000 conversion versus five annual conversions
Consider a simplified single taxpayer with $80,000 of taxable income before conversions. Assume income and federal thresholds remain constant solely to isolate the effect of timing.
| Strategy | Conversion schedule | Approximate incremental federal tax |
|---|---|---|
| One-time conversion | $300,000 in 2026 | $89,971 |
| Five-year conversion | $60,000 per year for five years | $69,430 total |
In this illustration, the one-time conversion reaches the 32% and 35% brackets. The annual $60,000 conversions remain within the 22% and 24% brackets, producing an estimated federal-tax difference of about $20,541.
This is not a forecast. A real comparison must include bracket inflation, investment growth, changing income, state taxes, Medicare costs, and the opportunity cost of paying tax sooner. A one-time conversion can still be reasonable when the account is expected to grow rapidly, a future tax increase is anticipated, or estate-planning considerations outweigh the immediate rate.
Use low-income retirement years strategically
The most useful conversion window often begins after employment income ends and before required minimum distributions begin. RMDs generally start at age 73 for people born from 1951 through 1959 and at age 75 for people born in 1960 or later.
A retiree who delays Social Security may have several years with unusually low taxable income. Larger conversions during those years may fill the 12%, 22%, or 24% brackets before Social Security and RMDs raise baseline income.
Adjust conversions around business income
Business owners should update projections as K-1 income becomes clearer. A practical schedule might include:
- No conversion during a high-income business-sale year
- A moderate conversion during a normal operating year
- A larger conversion during a year with heavy reinvestment, losses, or unusually low K-1 income
Quarterly projections are especially important because an unexpected distribution or sale can eliminate the bracket room that appeared available at the beginning of the year.
Estimate the reduction in future RMDs
Suppose a traditional IRA would otherwise be worth $1.5 million at age 73. Using the IRS Uniform Lifetime Table divisor of 26.5, the first-year RMD would be approximately $56,604.
If prior conversions reduced that balance to $1 million, the comparable RMD would be approximately $37,736—a difference of about $18,868. Actual results depend on investment performance, withdrawals, future conversions, and the applicable distribution table.
Taxes and Retirement Benefits the Calculator Must Include
Ordinary income tax
Pre-tax amounts converted from a traditional retirement account are generally taxed as ordinary income. A conversion is not taxed at a special Roth rate.
The IRA pro-rata rule
If you hold both deductible and nondeductible money in traditional, SEP, or SIMPLE IRAs, you generally cannot select only the after-tax dollars for conversion. The taxable and nontaxable portions are determined proportionally using your basis and the value of all such IRAs, generally including year-end balances.
Employer plans such as a 401(k) are not included in the IRA aggregation calculation, although converting pre-tax employer-plan funds is still generally taxable. Form 8606 is used to track nondeductible IRA basis.
Social Security taxation
A conversion can increase provisional income and cause more Social Security benefits to become taxable. Up to 85% of benefits may be included in taxable income. This interaction can create a higher effective marginal rate than the published bracket alone suggests.
Medicare IRMAA premiums
Higher modified adjusted gross income can increase Medicare Part B and Part D premiums. Medicare generally uses tax-return information from two years earlier, so a 2026 conversion will typically affect 2028 premiums.
IRMAA operates with threshold-based surcharges. A conversion that moves income just above a threshold may increase premiums for an entire year. Couples should also model the potential change from joint to single filing after the death of a spouse.
Deductions and other tax benefits
Conversion income may reduce or eliminate income-based deductions and credits. Depending on the taxpayer, relevant items can include the additional senior deduction, qualified business income deduction, deductible medical expenses, charitable deductions tied to adjusted gross income, and the income-based phaseout of the state and local tax deduction.
The real cost of a conversion is therefore:
Additional federal tax + state tax + lost tax benefits + related Medicare costs
Year-end deadline
A conversion generally must be completed by December 31 to count for that tax year. Unlike an IRA contribution, it cannot normally be designated for the prior year by completing it before the following April tax deadline. Begin the process early enough to allow the custodian to transfer and settle the assets.
2026 Roth Conversion Examples and Decision Checklist
Recently retired couple with a $1.5 million IRA
A married couple receives pension income but has not started RMDs. Their calculator should compare annual conversions through their chosen bracket against doing nothing. It should also show the loss of any senior deduction, potential IRMAA exposure, projected RMDs, and taxes for the surviving spouse filing as single.
Single retiree with $150,000 of taxable income
A single retiree with $150,000 of taxable income has preliminary bracket room of $51,775 before reaching $201,775. The first scenario might convert the full amount. Lower scenarios could stop below an IRMAA or deduction threshold, while a higher scenario could intentionally enter the next bracket if future RMDs are expected to be substantial.
Business owner approaching a sale
A business owner expecting a high-income sale year may skip the conversion that year. The owner can instead model larger conversions during lower-income years before or after the transaction. Estimated payments and state residency should be reviewed as part of the plan.
Final decision checklist
- Calculate tax both with and without the conversion.
- Compare the conversion’s marginal tax rate with expected future withdrawal rates.
- Run low, medium, and high conversion scenarios.
- Include state tax, Social Security, IRMAA, deductions, and capital gains.
- Verify nondeductible IRA basis and the pro-rata calculation.
- Estimate future RMDs under each scenario.
- Consider paying tax from cash or taxable assets so the full converted amount can remain invested.
- Review the projection quarterly and again before year-end.
- Allow time for the custodian to complete the conversion by December 31.
- Confirm the final amount and estimated-tax requirements with a tax professional.
What to Do Next
Start with three projections: a conservative conversion that avoids major income thresholds, a bracket-filling conversion, and a larger conversion that accepts a higher current tax rate to reduce future RMDs. Compare current tax, Medicare effects, projected retirement taxes, and ending traditional and Roth balances—not just the conversion tax in isolation.
The best annual amount is usually the one that uses intentionally selected tax brackets while accounting for future income and hidden marginal costs. For many households, that means a series of measured conversions rather than one all-or-nothing transaction.
This article provides general educational information and estimates, not individualized tax, legal, or investment advice. Verify current thresholds and rules with the IRS, Medicare, your account custodian, and a qualified professional before acting.