Why are Lines 4a and 4b different amounts?

Line 4a is the gross distribution from Form 1099-R; Line 4b is the taxable part. They match when the payout is fully taxable, and differ when part is nontaxable basis or a rollover.

Where does a rollover show up on the return?

A timely rollover still appears in gross on Line 4a, but the rolled-over amount is excluded from Line 4b so it is not taxed as income.

Is a Roth conversion taxable?

Generally yes — a traditional-to-Roth conversion is a taxable distribution reported on Line 4b to the extent of pre-tax dollars, even though the money stays in a retirement account.

2025 Form 1040, Lines 4a & 4b

IRA Distributions: Lines 4a & 4b Explained

By Paul D. Diaz, EA, MBA · Updated September 20, 2026

IRA distributions — 2025 Form 1040, Lines 4a & 4b — report gross IRA payouts from Form 1099-R on Line 4a and the taxable portion on Line 4b. Nontaxable basis, trustee-to-trustee rollovers, and Roth conversions each land differently.

Gross on 4a, taxable on 4b

Box 1 of Form 1099-R flows to Line 4a as the gross distribution, generally taxable under §408(d) and §402(a). When the entire payout is taxable, 4a and 4b match. Nondeductible contributions create basis tracked on Form 8606, and only the earnings portion above that basis lands on 4b — check the 1099-R 'taxable amount not determined' box and do the worksheet rather than assuming the full amount is taxable.

Rollovers vs. Roth conversions

A timely rollover to another IRA still shows in gross on 4a but is excluded from taxable 4b. A trustee-to-trustee transfer is the cleanest path. A Roth conversion is the opposite: deliberately taxable on 4b to the extent of pre-tax dollars, trading today's tax for qualified Roth treatment later.

What trips people up

Missing Forms 8606 that turn already-taxed basis into double-taxed income, indirect rollovers that miss the deadline, and withholding elections that surprise at filing time. Keep every 1099-R and track basis every year you touch an IRA.

From the practice: How retirement income flows onto the return →

Questions, answered

Why are Lines 4a and 4b different amounts?: Line 4a is the gross distribution from Form 1099-R; Line 4b is the taxable part. They match when the payout is fully taxable, and differ when part is nontaxable basis or a rollover.
Where does a rollover show up on the return?: A timely rollover still appears in gross on Line 4a, but the rolled-over amount is excluded from Line 4b so it is not taxed as income.
Is a Roth conversion taxable?: Generally yes — a traditional-to-Roth conversion is a taxable distribution reported on Line 4b to the extent of pre-tax dollars, even though the money stays in a retirement account.

Keep reading: Pensions & Annuities · Social Security Benefits · Total Income

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