VerCalc
US
Taxes
Backdoor Roth Ira Converter
Federal • 2026 • Pro‑rata (Form 8606 style)

Backdoor Roth IRA Converter

Estimate the taxable portion of a conversion via the pro‑rata rule, and see the incremental federal income tax impact.

Inputs

Planning calculator — validate final numbers on Form 8606 in your tax software.

Federal tax impact (simplified)

Estimated result

Basis ratio (planning)
10%
Non‑taxable conversion
$700
Taxable conversion (adds to income)
$6,300
Basis remaining (estimate): $6,300
Federal tax before conversion (after credits)
$17,570
Federal tax after conversion (after credits)
$19,046
Incremental federal tax (estimate)
$1,476
Accuracy note

Pro‑rata math on Form 8606 depends on your full IRA picture and year‑end balances. This calculator is a planning model, not filing advice.

Calculator inputs stay on your device (local processing).

Disclaimer: All calculators on this website are provided for informational and illustrative purposes only. The results do not constitute professional advice (including legal, tax, financial, medical, or other advice). Despite careful programming, we assume no liability for the accuracy, completeness, or timeliness of the results. For matters requiring professional advice, we recommend consulting an appropriate specialist (e.g., a tax advisor, lawyer, accountant, or physician).

Notes & examples

What this calculator does (and doesn’t)


This tool estimates the federal impact of a Backdoor Roth conversion:


•Pro‑rata rule: estimates what portion of your conversion is taxable vs non‑taxable
•Federal income tax impact: compares your estimated tax **before vs after** adding the taxable conversion

It does not model every IRS detail (all Form 8606 lines, timing, distributions, rollovers, penalties, AMT, state taxes). Use it for planning and verify with your tax software.


Pro‑rata rule (plain English)


If you have any pre‑tax money in Traditional/SEP/SIMPLE IRAs, the IRS generally treats your conversion as coming from a mix of after‑tax basis and pre‑tax dollars.


The key idea is the basis ratio:


•Basis ratio = `after‑tax basis ÷ total non‑Roth IRA value`
•Non‑taxable conversion ≈ conversion × basis ratio
•Taxable conversion ≈ conversion − non‑taxable portion

This is why having large pre‑tax IRA balances can make a Backdoor Roth largely taxable.


Quick example


Inputs
Value
After‑tax basis
$7,000
Total non‑Roth IRA value
$70,000
Conversion
$7,000

Basis ratio = 10%. Non‑taxable ≈ $700 and taxable ≈ $6,300.


High‑intent tips (common planning moves)


•Avoiding pro‑rata: many people try to have $0 pre‑tax Traditional/SEP/SIMPLE IRA balance at year‑end (often via a 401(k) rollover, if eligible).
•Track basis carefully: basis is typically tracked on Form 8606; losing track can create double taxation.
•Conversions can push you into a higher bracket: this tool shows your incremental federal tax from the taxable portion.

Related tools


•Planning retirement contributions? [401(k) / IRA Tax Savings](/us/taxes/401k-ira-tax-savings)
•Need a general federal estimate? [Tax Refund Estimator](/us/taxes/tax-refund-estimator)
•Choosing deductions? [Standard vs Itemized](/us/taxes/standard-vs-itemized-deductions)

FAQ (10)

Is a Backdoor Roth conversion taxable?

Often partially. If you have pre‑tax Traditional/SEP/SIMPLE IRA balances, the pro‑rata rule can make most of the conversion taxable. If your only IRA dollars are after‑tax basis, the taxable portion can be close to $0.

What is the pro‑rata rule?

It’s an IRS rule that treats IRA conversions as coming proportionally from after‑tax basis and pre‑tax funds across all your Traditional/SEP/SIMPLE IRAs (not account‑by‑account).

Does a 401(k) count in the pro‑rata rule?

Typically, no—401(k) plans are not included in the Form 8606 IRA pro‑rata pool. The pro‑rata rule is generally about Traditional/SEP/SIMPLE IRAs. Confirm your situation with a professional.

What is ‘IRA basis’?

Basis is your after‑tax (nondeductible) IRA contributions that haven’t been recovered yet. It’s typically tracked on Form 8606.

How does this calculator estimate tax impact?

It computes federal income tax on your estimated AGI before conversion and after adding the taxable conversion portion, then reports the difference as incremental tax (after optional non‑refundable credits).

Does this include penalties for early withdrawals?

No. This tool is about conversion taxation. Penalties depend on age, timing, and IRS rules.

Does this include state taxes?

No. State treatment varies; add your state marginal rate separately if you want a rough combined estimate.

Does this include the 5‑year rules?

No. Roth conversion 5‑year rules are important for withdrawals. This calculator focuses on the conversion’s taxable amount and federal tax impact.

What inputs do I need from last year’s return?

Your prior basis (Form 8606) and an estimate of your total non‑Roth IRA value. If you’re not sure, use conservative estimates and rerun later.

Is this accurate enough to file?

Use it for planning. Filing requires Form 8606 details and your full return context. Always verify in tax software or with a tax professional.