What this line means
The sum of your regular tax (line 16) and any additional taxes from Schedule 2 (line 17). This is your total tax before any credits are applied. Credits on lines 19 through 21 will reduce this number. Think of this as your tax bill before the government gives you credit for things like children, education, and other qualifying expenses.
Does this apply to you?
Easy to overlook
Credits reduce tax dollar-for-dollar, unlike deductions A $2,000 credit on line 19 reduces your tax by exactly $2,000. A $2,000 deduction only reduces your tax by $2,000 times your marginal tax rate (maybe $440 to $740). This is why the lines after line 18 are so valuable — every dollar of credit saves a full dollar of tax. 1 General filing pattern — credits confused with deductions
Line 18 can be zero even with income If your deductions reduced taxable income to zero on line 15, line 16 is zero, and line 18 is likely zero as well (unless you have AMT or other Schedule 2 taxes). Having zero tax before credits means credits on lines 19-21 have nothing to reduce — which is why some credits are “refundable” (they pay you even if your tax is zero) and appear later in the payments section. 2 IRS Form 1040 instructions — Line 18 computation
Watch out for this
Applying credits before adding Schedule 2 additional taxes. The order matters: first add all taxes (lines 16 + 17 = line 18), then subtract credits. If you apply the Child Tax Credit against line 16 before adding AMT from line 17, you understate your tax liability.
Footnotes
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IRS Form 1040 Instructions. See also IRS Publication 17, Your Federal Income Tax. https://www.irs.gov/pub/irs-pdf/p17.pdf ↩
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IRS Form 1040 Instructions, Line 18. https://www.irs.gov/instructions/i1040 ↩