The standard deduction is the floor
The standard deduction is available to everyone and needs no documentation. Under the 2026 figures a single filer takes $16,100 off income before the brackets, a joint filer $32,200 and head of household $24,150. Additional amounts for being 65 or older, or blind, sit outside this page.
It is the default that itemizing has to beat, and in recent years it usually does - mortgage interest, taxes and charity rarely add up to the standard amount for a household without a large mortgage or unusually heavy giving.
The comparison is strict: the itemized total must be larger than the standard deduction to replace it. A tie leaves the standard deduction in place and the hero prints a gap of $0, because there is nothing to gain from switching when the two land on the same number.
Itemizing adds up the Schedule A lines
The itemized total is five inputs added together: mortgage interest, state and local taxes, charitable gifts, medical and dental expenses, and other itemized amounts such as casualty losses or gambling losses. Charity is not added at the figure you type: the 2026 floor takes 0.5% of adjusted gross income off it first.
The state and local tax line is the one that gets adjusted. The figure you enter is capped at the 2026 SALT limit, which is $40,400 below $505,000 of income, drops by 30% of the excess above that, and never falls below $10,000. The page has no separate modified-AGI field, so gross income stands in for it; when the taxes you enter exceed the limit, a warning note shows how much does not deduct.
Medical is the other line that gets adjusted. The field asks for your medical and dental expenses for the year, and the page applies the 7.5%-of-AGI floor itself: 7.5% of adjusted gross income (gross income standing in for AGI) is subtracted first, so only the part that clears the floor reaches the itemized total. Charity has a floor of its own from 2026: only the part of your gifts that is more than 0.5% of adjusted gross income reaches the itemized total, so a small gift deducts nothing. Nothing else on the page caps the itemized total by income; the other lines are bounded only by the money ceiling.
The bigger deduction wins, priced at the margin
Whichever deduction is larger is the one you take, but the number that matters is the tax difference. The page walks the federal brackets twice - once on gross income minus the standard deduction, once on gross income minus the itemized total - and reports the difference, floored at zero so the loser never shows a negative saving.
At the default single return the itemized lines total $25,100 against a $16,100 standard deduction, so itemizing wins by $9,000, and the exact bracket difference is about $1,980 at a 22% marginal rate. A smaller mortgage flips the answer: $8,000 of interest, no SALT, $2,000 of charity and the default $1,000 of other itemized total $10,600, which is $5,500 short and loses.
The hero names the winner and the gap in whole dollars, and the stat line prices the tax saved by the larger deduction. The second table repeats the same figures one row per Schedule A line, so the total can be checked against your own receipts rather than trusted as a lump.
The tax column matters, not the deduction column
A $1,000 bigger deduction is worth $220 to a filer in the 22% bracket, not $1,000. The deduction reduces the taxable base the brackets see rather than the tax bill directly, and the marginal rate printed here is the rate at the taxable income produced by the standard deduction, so the shorthand and the exact figure start from the same place.
The logic holds for a single year. Bunching deductions into one year and taking the standard deduction in the next is a common planning move precisely because the standard deduction is all-or-nothing, and this page prices one year at a time.
What it leaves out is worth naming: the mortgage-interest limits on very large loans, the casualty-loss rules, the alternative minimum tax, and the way states treat itemized deductions. Those can change the answer at the margins, which is why the figure is an estimate from the numbers you enter rather than a return or tax advice.
Danfio