2025 Form 1040, Line 15
Taxable Income: Line 15, Where Tax Begins
2025 Form 1040, Line 15 — taxable income: AGI (Line 11) minus your deduction (Line 12) and QBI (Line 13) under IRC §63. The number the rate tables actually multiply — see Guide Ch. 3.
The last subtraction
Standard or itemized — whichever is larger comes off AGI here, plus the §199A QBI deduction for eligible business owners. If deductions wipe out AGI, you enter zero: no income tax. The form floors at zero; individuals get no negative.
Why two numbers matter
AGI gates the phaseouts, credits, and Medicare premiums; taxable income drives the actual tax computation on Line 16. Planning that moves one without the other — QBI, muni interest, Roth conversions — is where the real leverage hides.
From the practice: QBI shrinks Line 15 without touching AGI — so it cuts tax while leaving every AGI-gated benefit intact. Deductions, at book length →
Questions, answered
- AGI vs. taxable income — which matters?
- Both, differently. AGI (Line 11) gates phaseouts, credits, and Medicare premiums. Taxable income (Line 15) is what the rate tables actually multiply.
- Can Line 15 be zero or negative?
- Zero yes — if deductions wipe out AGI, you enter 0 and owe no income tax. Negative no — the form floors at zero; excess doesn't carry as NOL for individuals here.
- Does QBI come off before Line 15?
- Yes — the §199A qualified business income deduction (Line 13) subtracts after AGI, so it shrinks Line 15 without touching AGI-gated items.
Keep reading: AGI (Line 11) · Standard Deduction (Line 12) · Refund or Owed