Tool · High Earners
Backdoor Roth & Pro-Rata Calculator
See what your non-deductible IRA contribution and conversion will actually cost under IRC §408(d)(2) — the pro-rata rule that blends every dollar in your Traditional, SEP, and SIMPLE IRAs into one taxable pool. Compare as-is, reverse-rollover, and clean-slate scenarios side by side.
All calculations run locally in your browser. Your inputs are never transmitted or stored.
Step 1
Your existing IRA balances
What sits in your Traditional, SEP, or SIMPLE IRAs before this year's contribution. Projected to Dec 31.
Step 2
This year's backdoor plan
The non-deductible contribution and subsequent Roth conversion.
Step 3
Tax context
Marginal rates applied to the taxable portion of the conversion.
Step 4 (optional)
Reverse rollover scenario
Modeling what happens if you first roll pre-tax IRA balance into a workplace 401(k), which is not counted in pro-rata aggregation.
Current plan (as-is, with existing pre-tax IRAs)
Taxable portion
% of conversion
Total tax owed
federal + state
Net Roth received
after paying conversion tax
Pro-Rata Computation (Form 8606 Part I)
Line-by-line mirror of IRS Form 8606, Part I. Every line label is the actual form line. The formula is Line 10 = Line 3 ÷ Line 9 — your basis divided by the total pool the basis spreads across.
| This year's non-deductible contributionTracked via Form 8606 Part I. | |
| Prior-year basis carryoverFrom your most recent Form 8606 line 14. | |
| Total basis in Trad IRAs | |
| Dec 31 balance of all Trad/SEP/SIMPLE IRAsAfter conversion; excludes 401(k), 403(b), Roth, inherited. | |
| Other distributions (not conversion)This tool assumes zero; adjust mentally if you took distributions. | |
| Amount converted to Roth | |
| Denominator (6 + 7 + 8) | |
| Non-taxable fraction (3 ÷ 9) | |
| Non-taxable conversion (8 × 10) | |
| Taxable portion (8 − 11) | |
| Basis carried to next year (3 − 11) |
Three paths forward
The same contribution, converted under three different starting conditions. Only the pre-tax side of the ledger changes.
A · As-is
Tax bill on conversion
Pre-tax pool:
% taxable · basis carried:
B · Reverse rollover first
Tax bill on conversion
Rolled into 401(k):
Savings vs. as-is:
Requires workplace plan that accepts IRA rollover-in.
C · Clean slate
Tax bill on conversion
Zero pre-tax IRA balance
The mathematically ideal backdoor. Only possible if you've already cleared your pre-tax pool.
What this means
Methodology & citations
Pro-rata formula — IRC §408(d)(2) and Form 8606 Part I
The pro-rata rule flows from IRC §408(d)(2), which requires aggregating all Traditional, SEP, and SIMPLE IRAs when computing the taxable portion of a distribution or conversion. IRS Form 8606 Part I implements the statute as a ratio:
non-taxable fraction = total basis / (Dec 31 balance + distributions + conversions) non-taxable $ of conversion = conversion × non-taxable fraction taxable $ of conversion = conversion − non-taxable $ residual basis next year = total basis − non-taxable $ of conversionThree practical consequences: (a) you cannot "convert just the after-tax portion" — the IRS spreads basis across every aggregated dollar; (b) the December 31 balance matters, not the balance on the conversion date, so last-minute rollouts can fail; (c) basis that doesn't come out in the current conversion carries forward to next year and reduces future conversion taxes proportionally.
What counts (and what doesn't) in the aggregation
Counted in the pro-rata pool: Traditional IRAs (all of them, across all institutions), SEP IRAs, SIMPLE IRAs.
Not counted: 401(k), 403(b), 457(b), Thrift Savings Plan, Solo 401(k), defined-benefit pensions — any employer-qualified plan. Also: Roth IRAs (obviously), inherited IRAs from someone other than your spouse (they're tracked separately), and your spouse's IRAs (each spouse has their own pro-rata pool).
This asymmetry is the entire basis for the "reverse rollover" planning move: because workplace plans aren't aggregated, moving pre-tax IRA money into a 401(k) that accepts rollovers-in can sanitize your Traditional IRA to zero basis and enable a clean backdoor.
Reverse rollover strategy — mechanics and caveats
The move: before executing the backdoor, request a direct rollover of your pre-tax Traditional IRA balance into your current employer's 401(k). After the rollover lands, your pre-tax IRA pool reads zero. You then contribute the non-deductible amount to a fresh (or newly-refilled) Trad IRA and immediately convert it — 100% of which is basis, 0% taxable.
Prerequisites: (1) your employer's plan must accept rollovers from Traditional IRAs — not all do, and those that do often require a specific paperwork path. (2) Only pre-tax dollars are eligible to roll into a 401(k); non-deductible basis must be left behind or rolled to Roth IRA. (3) The Dec 31 balance is what matters for that year's pro-rata — so complete the rollover well before year-end.
Drawbacks: 401(k) plans typically offer fewer investment choices than IRAs and may have higher expense ratios. You lose the ability to take penalty-free withdrawals under §72(t)'s IRA-only provisions (SOSEPP, first-time home purchase, higher education).
Step-transaction doctrine — is the "wait period" real?
For years, there was ambiguity over whether the IRS could collapse a non-deductible contribution + immediate conversion into a single transaction (a direct Roth contribution, which high earners can't make). This concern caused practitioners to recommend a year-long delay between contribution and conversion.
The concern was substantially resolved by informal IRS comments and the Tax Cuts and Jobs Act's 2017 conference report, which explicitly acknowledged the backdoor Roth as a legitimate strategy. The IRS has not successfully challenged a same-day backdoor Roth conversion. Most tax professionals today treat immediate conversion as safe, and in fact recommend it to minimize the earnings creep between contribution and conversion (because any earnings are taxable on conversion).
That said, there is no formal regulation eliminating step-transaction risk, so conservative taxpayers sometimes wait a few days to a few weeks. A full year's wait is almost certainly overkill.
Form 8606 filing — the paper trail
Form 8606 must be filed whenever you: (a) make a non-deductible Traditional IRA contribution; (b) take a distribution or conversion from a Traditional, SEP, or SIMPLE IRA that has basis; or (c) have basis carrying over from prior years even if you took no action.
Part I computes the non-taxable fraction of your distributions/conversions using the line structure this tool mirrors. The output of Line 14 (residual basis) becomes next year's Line 2 opening balance — which is why forgetting to file Form 8606 one year can compound into a decade of lost basis tracking.
Part II reports the Roth conversion amount and the taxable portion (Line 11 taxable amount flows through). Part III handles non-qualified Roth distributions.
The IRS has a $50 penalty for failing to file Form 8606 when required, and a $100 penalty for overstating basis. Lost basis costs the taxpayer far more: if the IRS can't verify your basis, your entire Trad IRA is presumed to be pre-tax on future distributions.
Spousal aggregation — it's per-person, not per-couple
Even for married-filing-jointly couples, IRAs are owned individually and the pro-rata aggregation is computed separately for each spouse. This creates a frequently-overlooked planning opportunity: if one spouse has pre-tax IRA money and the other has none, the clean-pool spouse can execute a backdoor Roth without pro-rata drag, even while the other spouse's IRAs are "polluted." The couple can still contribute to both spouses' Roth IRAs (up to each spouse's annual limit) with only one spouse bearing the backdoor-Roth friction.
Inherited IRAs from a non-spouse also stay out of your aggregation — they're tracked under a separate basis pool owned by you as beneficiary.
When does a backdoor Roth not make sense?
Three situations where this calculator may show near-zero benefit:
- Large pre-tax IRA balance you can't roll out. If your employer plan won't accept rollover-ins and you have substantial pre-tax IRA balances, every backdoor conversion will be mostly-taxable. You're just paying income tax now to move money from a Trad IRA to a Roth IRA — which may or may not beat leaving it in the Trad IRA, depending on your current vs. future marginal rate.
- You'll be in a lower bracket in retirement. The backdoor converts at today's marginal rate. If retirement rates will be meaningfully lower, a non-deductible Traditional IRA contribution with no conversion (or a Roth 401(k) contribution via work) may dominate.
- Your MAGI is below the direct-contribution cliff. If your MAGI is already inside the phase-out or below it, you can contribute directly to Roth IRA up to your reduced limit — no backdoor needed. Check the MAGI Estimator.
Sources & primary authorities
- IRC §408(d)(2) — pro-rata aggregation of IRA distributions
- IRC §408A(d)(3) — conversion rules and the 2010 removal of the income limit on Roth conversions
- IRS Form 8606 (current year) Parts I–III, and the Form 8606 Instructions
- IRS Publication 590-A — contributions to IRAs (non-deductible contribution rules)
- IRS Publication 590-B — distributions from IRAs (pro-rata examples)
- IRS Notice 2014-54 — allocation rules for rollovers from qualified plans (relevant context for what plans can accept rollovers)
- TCJA 2017 Conference Report — legislative acknowledgment of backdoor Roth as a legitimate strategy
- 2026 IRA contribution limits: IRS Notice 2025-67 ($7,500 base, $1,100 catch-up for age 50+)
This tool projects federal and state income-tax impact based on your entered marginal rates. It does not model NIIT (§1411), state-specific modifications to Roth conversion income, or Medicare IRMAA surcharges that may apply when conversion income crosses MAGI thresholds. Consult a tax professional for your full situation.
User Guide
How to use the Backdoor Roth Calculator
The Backdoor Roth is a two-step technique: contribute to a non-deductible Traditional IRA (no income limit), then convert immediately to a Roth IRA. The strategy works cleanly when you have no other pre-tax IRA money. It works messily — sometimes prohibitively — when you do. This tool applies the actual IRS formula (the pro-rata rule, IRC §408(d)(2)) to your exact balances and tells you how many dollars of your conversion end up taxable, how much ends up tax-free, and whether the technique is worth executing at all.
The reason this tool exists: virtually every "backdoor Roth calculator" on the internet assumes your pro-rata tax is zero. That's only true if you have zero other Traditional IRAs. If you have any pre-tax IRA money — a rollover from a former 401(k), a SEP-IRA, a SIMPLE IRA past the two-year holding period — the pro-rata rule aggregates everything, and a non-trivial share of your "non-deductible" conversion becomes taxable anyway.
Who should use this tool
High-income workers whose MAGI exceeds the Roth phase-out cliff and who are considering the Backdoor Roth. The tool is most critical for those with existing pre-tax IRA balances — because the pro-rata rule can erode most of the technique's value. It's also useful for taxpayers who still have time to "empty" their Traditional IRA by rolling it into an employer 401(k) (if the plan accepts incoming rollovers), because the tool models what the Backdoor looks like after such a reverse rollover.
If you have no pre-tax IRA balances at all, the tool is still useful for documenting basis correctly on Form 8606 and for confirming timing — the order of the contribution and the conversion doesn't matter mechanically, but the tax-year reporting does.
Walking through the inputs
The Backdoor contribution amount. Up to the 2026 combined IRA limit, $7,500 ($8,600 if age 50+). The tool assumes this is fully non-deductible — because if you could deduct it, you'd be under the Roth direct-contribution limit anyway and wouldn't need the Backdoor.
Pre-tax IRA balances as of December 31, 2026. This is the number that breaks most simple calculators. Enter the aggregate balance across all your Traditional IRAs, SEP-IRAs, and SIMPLE IRAs. Do not include your spouse's IRAs (pro-rata is per-taxpayer, not per-couple) and do not include 401(k) or 403(b) balances (employer plans are excluded from the aggregation).
After-tax basis in those balances. If you've made previous non-deductible contributions and properly tracked them on Form 8606, enter the cumulative basis. Most people's basis is zero unless they've been doing the Backdoor for years.
Your marginal rate. The rate that applies to the taxable portion of the conversion. For most Backdoor users, this is the top bracket they already pay — 32% or 35%.
How to read the result
The tool returns three numbers. Tax-free portion is what converts cleanly — the non-deductible contribution you just made, prorated by the basis-to-balance ratio. Taxable portion is the remainder, which becomes ordinary income in the conversion year. Effective tax cost is the taxable portion multiplied by your marginal rate.
If your only IRA is the $7,500 Backdoor contribution and you convert it in the same year with zero pre-existing balances, the taxable portion is zero (or nearly zero — just whatever grew between contribution and conversion) and the Backdoor is a clean technique. If you have $200,000 in a rollover IRA and you contribute $7,500 non-deductible and convert $7,500, the pro-rata formula says only 3.6% of your conversion is basis; the other 96.4% is taxable. You'd pay tax on roughly $7,230 of the $7,500 conversion — and the remaining $193K of pre-tax money still sits in the Traditional IRA mixed with your unconverted basis.
The tool also shows the "reverse rollover" scenario: if your employer 401(k) accepts an incoming rollover of your Traditional IRA, you can empty the Traditional, execute the Backdoor cleanly, and have no pro-rata pain. The tool shows the tax picture with and without the reverse rollover so you can decide whether it's worth pursuing.
Common mistakes this tool prevents
- Converting without checking your other IRA balances. If you have a rollover IRA and you don't realize the pro-rata rule aggregates, you'll get surprised by a 1099-R showing a much larger taxable amount than you expected.
- Including 401(k) balances in the aggregation. Employer plans are excluded. Only IRAs (Traditional, SEP, SIMPLE past two years) count.
- Including the spouse's IRAs. Pro-rata is per-taxpayer. Each spouse's Backdoor is computed against their own IRA aggregation.
- Forgetting Form 8606. Every non-deductible contribution and every partial conversion must be reported on Form 8606 to establish basis. Lose the paper trail and the IRS treats everything as pre-tax.
- Confusing the five-year clock. Backdoor conversions are still conversions — each one starts its own five-year clock for withdrawing the converted principal tax-and-penalty-free before age 59½. If you're under 59½ and might need the money inside five years, don't Backdoor.
After you run the calculator
If the effective tax cost is small (under 5% of the conversion), execute the Backdoor immediately. If it's meaningful (above 25%), first attempt to roll your Traditional IRA into your employer 401(k), then re-run the calculator. If your employer plan doesn't accept incoming rollovers, the Backdoor may not be worth it versus simply directing the $7,500 to a taxable brokerage account with tax-efficient index funds — which is a perfectly reasonable fallback.
The companion pro-rata rule pillar walks through the formula with worked examples, and the Backdoor Roth pillar covers the reporting and the IRS step-transaction-doctrine history.