Form 1099-R box guide
Box 2b: Taxable amount not determined
The payer did not calculate the taxable portion.
What this box tells you
The payer did not calculate the taxable portion.
How to use it
Use your contribution basis, rollover records, and the applicable IRS worksheet to calculate it.
Where Box 2b flows on your return
Box 2b does not flow to Form 1040 directly — it is a flag, not a dollar amount. Once you calculate the real taxable amount yourself, that figure is what goes on Line 4b (IRA) or Line 5b (pension/annuity); the gross Box 1 amount still goes on Line 4a/5a.
How Box 2b works
Box 2b actually has two separate checkboxes: "Taxable amount not determined" and "Total distribution." The first means the payer could not figure out how much of the distribution is taxable — common for IRA trustees who do not track your basis across multiple accounts. The second just confirms the payment closed out the entire account; it does not by itself affect taxability.
When "Taxable amount not determined" is checked, Box 2a is usually blank or matches Box 1. You are responsible for computing the actual taxable amount: for a traditional IRA with nondeductible contributions, that means Form 8606 and the pro-rata basis calculation; for a pension with after-tax contributions, that means the Simplified Method Worksheet in the Form 1040 instructions.
Worked example
Priya's IRA custodian sends a 1099-R showing $18,000 in Box 1, Box 2a blank, and Box 2b's "Taxable amount not determined" box checked. Priya has $3,000 of nondeductible basis tracked on prior Forms 8606. Using the pro-rata formula, she determines $2,700 is nontaxable return of basis and $15,300 is taxable, which she reports on Line 4b.
Put the boxes together
The taxable result depends on more than one field. Use the calculator to combine gross distribution, taxable amount, withholding, contributions, rollover, QCD, age, and distribution code.
Open the 1099-R calculatorFrequently asked questions
Do I still owe tax if Box 2b is checked?
Usually yes, at least on part of the distribution. Box 2b just means the payer left the taxable-amount calculation to you — it does not mean the distribution is tax-free.
What records do I need to calculate the taxable amount myself?
Your cumulative nondeductible IRA basis from Form 8606 (for IRAs), or your total after-tax contributions and expected number of payments (for pensions, via the Simplified Method Worksheet).
Is "Total distribution" the same as "Taxable amount not determined"?
No — they are two separate checkboxes in the same box. "Total distribution" just means the account was closed out; it says nothing about how much of that payment is taxable.
Sources
Related Calculators
1099-R Tax Calculator
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1099-R Distribution Codes
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10% pre-59½ + income tax, first-home exception, SEPP 72(t)