Pro-Rata Rule Calculator

2026 rules

Follow the Form 8606 pro-rata calculation with your own numbers, line by line.

Your numbers

Amount converted this year (Form 8606 line 8)

Total basis: this year's plus prior nondeductible contributions (lines 1-3)

Value of all traditional, SEP and SIMPLE IRAs on Dec 31 (line 6)

Other distributions this year (line 7)

Result

Taxable part of the conversion$6,938

Line 9: total (6 + 7 + 8)$100,000
Line 10: basis ÷ line 90.07500
Line 11: nontaxable part of the conversion$563
Line 18: taxable conversion$6,938
Basis carried to 2027 (line 14)$6,938

How it works

Part I of Form 8606 adds your basis (all nondeductible contributions not yet recovered) and divides it by the total of your year-end traditional IRA value, any distributions and the amount converted.

That ratio is the nontaxable share of the conversion. The rest is taxable income, and the basis you didn't use carries forward to next year's form.

2026 figures: IRS Rev. Proc. 2025-32 (2026 inflation adjustments); IRS Notice 2025-67 (2026 retirement plan limits); CMS 2026 Medicare Parts A & B premiums and deductibles.

Questions

Why is the year-end value used and not the value when I converted?

The law measures all your IRAs at December 31, so money rolled in later in the year still affects a conversion made in January.

Do inherited IRAs count?

No. Inherited IRAs and Roth IRAs are left out of the pro-rata calculation.