Quick Answer
Quick Answer: The calculator treats a Roth conversion as ordinary income stacked on top of your current taxable income. It computes your 2026 federal tax before the conversion, then again with the conversion added, and the difference is the incremental tax you owe. For a single filer with $80,000 of taxable income who converts $50,000, the engine returns $11,486 of federal tax, a 24% marginal rate, a 22.97% effective rate, and a 2.17-year break-even at a 12% expected retirement rate. This page shows the complete math behind every number our calculator produces.
Key Takeaways
- The engine uses four required inputs -- conversion amount, age, filing status, and current taxable income -- plus two optional inputs for break-even (expected retirement rate and return)
- Tax owed is incremental: your 2026 federal tax with the conversion minus your tax without it
- The marginal rate is the top bracket the conversion reaches; the effective rate is tax owed divided by the conversion amount, and is usually lower
- Break-even years come from a log-ratio model comparing today's conversion rate with your expected retirement rate
- The figure is federal ordinary-income tax only -- state tax, IRMAA surcharges, and the per-conversion 5-year clock are out of scope
Roth Conversions in Plain English
A Roth conversion moves money from a pre-tax Traditional IRA (where you have never paid income tax on it) into a Roth IRA (where future growth and withdrawals are tax-free). The catch is that the converted amount is treated as ordinary income in the year you convert -- so you pay tax now to buy tax-free treatment later.
The calculator walks the same steps every time:
- Take your current taxable income and figure your 2026 federal tax on it.
- Add the conversion amount on top, and figure your federal tax again.
- Subtract the two: the increase is the tax the conversion costs you.
- Report the marginal bracket the conversion reaches, the effective (blended) rate, and -- if you supply an expected retirement rate -- how many years of tax-free growth it takes to break even.
The key idea is bracket stacking. Because federal brackets are progressive, the first dollars of a conversion are taxed at your current marginal rate, and later dollars can spill into the next bracket up. That is why doubling the conversion does not always double the tax -- and why "filling up a bracket" is a common conversion strategy. The IRS Roth conversion guidance(opens in new tab) is the authoritative reference for how conversions are taxed.
The Formula
Here are the exact rules used by our Roth Conversion Calculator. Let I be current taxable income and C the conversion amount. The engine runs a progressive bracket lookup (bracketTax) twice:
taxOwed = bracketTax(I + C) − bracketTax(I)
Where bracketTax(x) walks the 2026 brackets for your filing status: for the top bracket b that x reaches, bracketTax(x) = baseTaxb + (x − minb) × rateb. The engine then derives two rates:
marginalRate = rate of the top bracket that (I + C) reaches
effectiveRate = taxOwed ÷ C
If you supply an expected retirement marginal rate, the engine computes a break-even horizon with a log-ratio model. Let f = future (retirement) rate, m = conversion marginal rate, r = expected return:
if f ≥ m → breakEvenYears = 0 (immediate)
otherwise: breakEvenYears = ln((1 − f) ÷ (1 − m)) ÷ ln(1 + r)
Two rules the engine applies exactly:
- Tax floored at zero:
taxOwed = max(0, afterTax − beforeTax)-- a conversion never produces a negative tax. - 5-year rule flag: the engine returns
fiveYearRuleApplies = truewhen age is under 59½, because each conversion starts its own 5-year clock before earnings can be withdrawn penalty-free.
Variable Definitions
| Variable | Meaning | Units / How to Enter | Example (single, $80,000, convert $50,000) |
|---|---|---|---|
| C (conversionAmount) | Amount moved from Traditional to Roth | USD, 0 – 10,000,000 | $50,000 |
| I (currentTaxableIncome) | Taxable income before the conversion | USD, 0 – 10,000,000 | $80,000 |
| filingStatus | Which 2026 bracket table applies | single / married / marriedSeparate / headOfHousehold | single |
| age | Drives the 5-year-rule flag (under 59½) | Integer, 18 – 100 | 45 |
| f (retirementMarginalRatePercent) | Expected marginal rate in retirement | Percent, 0 – 50 (optional) | 12% |
| r (expectedReturnPercent) | Annual return on the converted balance | Percent, 0 – 20 (default 7) | 7% |
Valid Input Ranges
Our calculation engine accepts a conversion amount and current taxable income from $0 to $10,000,000, an age from 18 to 100, one of four filing statuses, an expected retirement rate from 0% to 50%, and an expected return from 0% to 20%. These bounds match the engine exactly.
Worked Example: Single Filer, $80,000 Income, Convert $50,000
This section walks through every step for a $50,000 conversion that crosses a bracket boundary. You can follow along and verify the result against our Roth Conversion Calculator. The 2026 single brackets used below are 10% to $12,400, 12% to $50,400, 22% to $105,700, and 24% to $201,775.
Step 1: Federal Tax Before the Conversion
- $80,000 falls in the 22% bracket ($50,400 – $105,700)
- Base tax at $50,400 = $5,800 ($1,240 at 10% + $4,560 at 12%)
- bracketTax($80,000) = $5,800 + ($80,000 − $50,400) × 0.22 = $12,312
Step 2: Federal Tax After Adding the Conversion
Adding $50,000 lifts taxable income to $130,000, which lands in the 24% bracket.
- Base tax at $105,700 = $17,966 ($5,800 + $55,300 at 22%)
- bracketTax($130,000) = $17,966 + ($130,000 − $105,700) × 0.24 = $23,798
Step 3: Incremental Tax Owed
- taxOwed = $23,798 − $12,312
- taxOwed = $11,486
Step 4: Marginal and Effective Rate
- Marginal rate = 24% (the top bracket $130,000 reaches)
- Effective rate = $11,486 ÷ $50,000 = 22.97%
Step 5: Break-Even Horizon
- f = 12% (retirement), m = 24% (conversion marginal), r = 7% (return)
- breakEvenYears = ln((1 − 0.12) ÷ (1 − 0.24)) ÷ ln(1.07)
- = ln(0.88 ÷ 0.76) ÷ ln(1.07) = 0.14660 ÷ 0.06766
- breakEvenYears = 2.17; and because age 45 is under 59½, the 5-year rule applies
Read together: this saver pays $11,486 in federal tax to convert $50,000 -- an effective rate of 22.97% -- and the move pays off after about 2.17 years of tax-free growth if they expect a 12% marginal rate in retirement. Every figure above was produced by the calculator's engine with inputs conversionAmount = $50,000, currentTaxableIncome = $80,000, filingStatus = single, age = 45, retirementMarginalRatePercent = 12, expectedReturnPercent = 7 (verified July 5, 2026).
How Conversion Size Changes the Tax
Because the brackets are progressive, the effective rate on a conversion climbs as more of it crosses into the next bracket up. The table below holds the filer fixed (single, $80,000 taxable income) and varies only the conversion amount. Every row was computed by the engine.
| Conversion Amount | Federal Tax Owed | Marginal Rate | Effective Rate |
|---|---|---|---|
| $10,000 | $2,200 | 22% | 22.00% |
| $25,000 | $5,500 | 22% | 22.00% |
| $50,000 (worked example) | $11,486 | 24% | 22.97% |
| $75,000 | $17,486 | 24% | 23.31% |
| $100,000 | $23,486 | 24% | 23.49% |
The first $25,700 of conversion room (from $80,000 up to the $105,700 bracket edge) is taxed entirely at 22%, so the $10,000 and $25,000 conversions carry a flat 22.00% effective rate. Once the conversion crosses $105,700, each additional dollar is taxed at 24%, dragging the blended effective rate upward toward that ceiling.
Filling Up a Bracket
A common strategy is to convert only enough to "fill" your current bracket without spilling into the next. For this filer, converting up to $25,700 keeps every dollar at 22%; the next dollar is taxed at 24%. The engine's marginal-rate output tells you exactly where that line sits for your income and filing status.
The Break-Even Horizon and the 5-Year Rule
Two levers sit outside the worked example: your expected retirement rate, which drives break-even, and the 5-year rule, which the engine flags. Both are encoded in the tool.
How the Expected Retirement Rate Moves Break-Even
The log-ratio model answers a simple question: how many years of tax-free growth does the converted balance need before the upfront tax pays for itself? The higher your expected retirement rate relative to today's conversion rate, the sooner the conversion wins. The table holds the conversion fixed (single, $80,000 income, convert $50,000, 7% return, 24% conversion marginal rate) and varies only the expected retirement rate. Every row is engine-computed.
| Expected Retirement Rate | Break-Even Years |
|---|---|
| 10% | 2.50 |
| 12% (worked example) | 2.17 |
| 22% | 0.38 |
| 24% (equals conversion rate) | 0.00 (immediate) |
| 32% | 0.00 (immediate) |
When your expected retirement rate reaches the rate the conversion is taxed at (24% here), break-even is immediate -- the rate arbitrage already favors converting, so the engine returns 0 years. Below that, the further your retirement rate sits under the conversion rate, the longer the horizon: at a 10% retirement rate the balance needs about 2.5 years of growth to pull even.
The 5-Year Rule Flag
For any saver under age 59½, the engine sets fiveYearRuleApplies = true. Each Roth conversion starts its own five-year clock: withdraw the converted principal before five years and before age 59½ and you may owe a 10% penalty on that amount. The engine reports whether the rule is in play based on age, but it does not model the per-conversion clock timing -- that is a planning detail to track separately.
Data Sources and Methodology Notes
Calculation Engine and API Access
The same conversion-tax logic runs in the browser and in our public calculator API / MCP server (tool: roth_conversion_tax_impact — full input/output schema in the API reference), so a result is identical wherever you access it. The engine returns the incremental tax owed, the marginal rate on the conversion, the effective rate, the 5-year-rule flag, and the optional break-even years. As a reproducibility check, the worked example and every table figure on this page were generated by that engine (verified July 5, 2026).
Reference Data
- The 2026 federal ordinary-income brackets used by the engine are set by IRS Revenue Procedure 2025-32 (2026 inflation adjustments)(opens in new tab). For a single filer these are 10% to $12,400, 12% to $50,400, 22% to $105,700, 24% to $201,775, 32% to $256,225, 35% to $640,600, and 37% above.
- Conversion taxation, the ordinary-income treatment, and the 5-year rule follow IRS guidance on rollovers and Roth conversions(opens in new tab) (see also Publication 590-A).
Assumptions and Scope Limits
- This tool models a single conversion only. Multi-year conversion "laddering" or optimization is a separate, future feature.
- Federal ordinary-income tax only. State income tax on the conversion and Medicare IRMAA premium surcharges are not modeled -- add them separately.
- The 5-year rule is reported as a flag (age under 59½); the engine does not model the per-conversion clock timing.
- Break-even is a simplified log-ratio heuristic (tax assumed paid from the converted amount; the unconverted side valued at today's after-tax dollars), not a year-by-year side-by-side projection.
- Figures are 2026 values. Brackets are re-indexed annually, so verify the current year before relying on any number.
Frequently Asked Questions
The calculator treats the conversion as ordinary income stacked on top of your existing taxable income. It computes your 2026 federal tax at your income before the conversion, then again with the conversion added, and the difference is the incremental tax you owe. For a single filer with $80,000 of taxable income converting $50,000, the engine returns $11,486 of federal tax -- because the conversion fills the rest of the 22% bracket and spills into the 24% bracket.
The marginal rate is the top bracket the conversion pushes you into -- 24% in the worked example, because $80,000 + $50,000 = $130,000 lands in the 2026 single 24% bracket. The effective rate is the total tax divided by the conversion amount: $11,486 ÷ $50,000 = 22.97%. The effective rate is lower than the marginal rate because part of the conversion is still taxed at 22% before the rest crosses into 24%.
Break-even uses a log-ratio model: breakEvenYears = ln((1 − futureRate) ÷ (1 − conversionMarginalRate)) ÷ ln(1 + expectedReturn). With a 12% expected retirement rate, a 24% conversion marginal rate, and a 7% return, the engine returns 2.17 years. If your expected retirement rate is at or above the conversion marginal rate, break-even is immediate (0 years) because the rate arbitrage already favors converting. State tax and IRMAA are not modeled in this figure.
No. By design the roth_conversion_tax_impact engine models federal ordinary-income tax only. State income tax on the conversion, Medicare IRMAA premium surcharges, and the per-conversion 5-year-rule clock are explicitly out of scope -- the tool reports whether the 5-year rule applies (age under 59½) but does not model the timing. Add your state's rate and check IRMAA thresholds separately.
Because the federal brackets are progressive. A $10,000 or $25,000 conversion on top of $80,000 stays inside the 22% bracket, so its effective rate is 22.00%. A $50,000 conversion pushes into the 24% bracket, raising the blended effective rate to 22.97%; a $100,000 conversion pushes further, reaching 23.49%. Each additional dollar above the $105,700 bracket edge is taxed at 24%, so the average rate on the whole conversion climbs toward that ceiling.
Sources
- Internal Revenue Service -- Revenue Procedure 2025-32 (2026 federal tax brackets and inflation adjustments)(opens in new tab)
- IRS -- IRA FAQs: Rollovers and Roth Conversions(opens in new tab)
- IRS Publication 590-A -- Contributions to Individual Retirement Arrangements (conversions and the 5-year rule)(opens in new tab)
Important Disclaimer
Disclaimer: This content is for educational and informational purposes only and does not constitute financial, tax, or legal advice. Individual circumstances vary, and you should consult with a qualified tax or financial professional before making conversion decisions. A Roth conversion is generally irreversible and can affect your state taxes, Medicare IRMAA premiums, and other income-based benefits that this tool does not model. Federal tax brackets are set by the IRS and change from year to year; the figures here are 2026 values. While we strive for accuracy, laws and regulations change over time. Data current as of July 2026.
Content reviewed by the Digital Calculator Team. Learn more about our accuracy standards.