Backdoor Roth IRA Pro-Rata Calculator (Form 8606)

How to do it

1. 1
   Step 1: Open Backdoor Roth IRA Pro-Rata Calculator (Form 8606) and add your input

   Type your numbers or text, add your file, or pick the options you need. Nothing is uploaded: everything stays in your browser.

2. 2
   Step 2: What Backdoor Roth IRA Pro-Rata Calculator (Form 8606) does

   Work out the taxable part of a backdoor Roth conversion under the pro-rata rule.

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   Step 3: Read the result and compare

   The result appears at once. Change one value to see how the answer moves, then keep the figure that fits your case.

4. 4
   Step 4: Copy or save it

   Copy the result or download it. For an important decision, confirm it with the official source or an adviser.

About this tool

Enter your non-deductible IRA contribution, any after-tax basis from earlier years, the year-end value of your other traditional, SEP and SIMPLE IRAs and the amount you convert. The tool applies the Form 8606 pro-rata rule and shows how much of the conversion is taxable.

The pro-rata rule

All your traditional, SEP and SIMPLE IRAs are treated as one account. The share of that account that is after-tax money (basis) is the share of any conversion that is tax free. The value used is the balance on December 31 plus the amount converted that year.

Example of the effect

With a $7,500 non-deductible contribution and $93,000 of pre-tax IRA money, only 7.46% of the conversion is tax free; the rest is taxed. If your other IRAs are empty, the whole conversion is tax free. Some people roll pre-tax IRA money into a workplace 401(k) before December 31 to avoid this.

Limits

The 2026 IRA contribution limit is $7,500 ($8,600 at age 50 or older); for 2025 it is $7,000 ($8,000). Enter the value after the conversion in the "other IRAs" box. Form 8606 is required every year you make a non-deductible contribution or convert.

Worked example

A $7,500 non-deductible contribution converted right away with $93,000 left in a traditional IRA: total value $100,500, tax-free share 7.46%, so $560 of the conversion is tax free and $6,940 is taxable, which costs about $1,666 at a 24% rate. The remaining basis of $6,940 stays in the IRA.

Tips for best results

Check every box before you rely on a result, because one wrong digit changes the whole answer. Use the exact figures from your payslip, bill, certificate or contract, and keep a note of the date you calculated. Rates, thresholds and rules change from time to time, so for tax, fees and legal matters treat the output as an estimate and confirm with the official source named on this page. You can run as many scenarios as you like; nothing is saved or sent, and refreshing the page clears the boxes.