Schedule A (Form 1040)

Schedule A is the attachment to Form 1040 on which an individual lists the deductions available only by electing to itemize. The form's own title, in the top left corner, is "Itemized Deductions", and its instruction line reads "Attach to Form 1040 or 1040-SR". Its structure is six labeled sections down the left margin, each collecting one category of deduction, with the results added on a single total line that carries to Form 1040.

The distinction worth drawing at the start is between the form and the decision. Whether to itemize at all, what the category contains, and how much a deduction is worth once you are inside it are the itemized deductions page's subject. Schedule A is the mechanism: which costs go on which line, which limits the form applies for you, and what the form implies you should have kept.

Section one, medical and dental, computes its own floor. You enter total unreimbursed medical and dental expenses, then adjusted gross income, then 7.5% of that figure, and subtract. Only the excess carries forward, and where the floor exceeds the expenses the line is zero rather than negative. The section's own caution reads "Do not include expenses reimbursed or paid by others", which is the point most often missed: an expense paid from a health savings account or a flexible spending account has already been excluded from income and cannot be deducted again.

Section two, taxes you paid, is where the cap lives. Line 5a takes either state and local income taxes or general sales taxes, and the form makes you choose by checking a box; you cannot deduct both. Line 5b is real estate tax and line 5c is personal property tax. Line 5d adds the three, and line 5e is where the state and local cap of $40,400 is applied, with half that amount for a married person filing separately, and with a reduction that starts once modified adjusted gross income passes $505,000. Line 6 collects other deductible taxes. The instructions also list the taxes that do not go here at all, and the list is longer than people expect: federal income tax, Social Security and Medicare tax, federal unemployment tax, foreign real property taxes, assessments for sidewalks and other improvements to your property, gasoline tax, car inspection fees, and license fees for a marriage, a driver or a pet.

Section three, interest you paid, separates the reported from the unreported. Line 8a is home mortgage interest and points reported to you on Form 1098, and 8b is mortgage interest not reported on a Form 1098, which requires you to name the person you paid, their identifying number and their address. Line 8c is points not reported on Form 1098. Line 9 is investment interest, which has its own limit computed on Form 4952. The header carries a checkbox for the case where the loan was not used entirely to buy, build or improve the home, because that is what decides whether the interest qualifies at all.

Section four, gifts to charity, is three lines and a great deal of substantiation. Line 11 is gifts by cash or check, line 12 is gifts of anything else, and line 13 is a carryover from a prior year, since amounts disallowed by the percentage ceilings generally carry forward for five years. The form itself flags the two documentation thresholds: any single gift of $250 or more needs a contemporaneous written acknowledgment from the charity, and noncash gifts totaling more than $500 need Form 8283. From 2026 a floor also applies, under section 170(b)(1)(I): charitable contributions are allowed only to the extent they exceed 0.5% of the contribution base, which section 170(b)(1)(H) defines as adjusted gross income. The first slice of an itemizer's giving therefore produces no deduction.

Section five is narrower than its name. Casualty and theft losses reach only losses attributable to a federally declared disaster, computed on Form 4684, and each separate loss must exceed $100 before it counts. From 2026 section 165(h)(5) also reaches a state declared disaster, meaning a natural catastrophe, fire, flood or explosion the state's governor and the Treasury agree is severe enough, which widens the section for the first time since the 2017 restriction. A net qualified disaster loss goes on line 16 rather than line 15, and can even be claimed by a taxpayer who is not itemizing, as an addition to the standard deduction.

Section six is a closed list. The instructions are explicit that "only the expenses listed next can be deducted on line 16", and the list is short: gambling losses to the extent of gambling winnings, and from 2026 also capped at 90% of the losses; casualty and theft losses of income-producing property, including losses from financial scams; federal estate tax on income in respect of a decedent; amortizable bond premium in certain cases; an ordinary loss on a contingent payment or inflation-indexed debt instrument; repayment of amounts under a claim of right over $3,000; certain unrecovered investment in a pension; and impairment-related work expenses of a disabled person. Line 16 is not a place for anything that does not appear there.

The total line and the checkbox below it. Line 17 adds the far right column and carries to Form 1040. Line 18 is a checkbox with no dollar amount, and the instructions explain it precisely: check it "if you elect to itemize for state tax or other purposes even though your itemized deductions are less than your standard deduction". Several states require a taxpayer to itemize on the state return only if they itemized federally, so deliberately taking a smaller federal deduction can produce a larger combined result. The other situation the checkbox covers is a married person filing separately whose spouse itemizes, since that leaves them with no standard deduction at all.

One caution applies to the whole form. The instructions carry it in a box: "Don't include on Schedule A items deducted elsewhere, such as on Form 1040, Form 1040-SR, Schedule 1-A, or Schedule C, E, or F." That matters more than it used to, because Schedule 1-A now carries the deductions for tips, overtime, car loan interest and the enhanced amount for seniors, which are available alongside the standard deduction and are not itemized deductions. A cost that belongs to a business goes on the business schedule, where it reduces adjusted gross income and does not depend on itemizing at all.

The form is filled in section by section, and the total is the only figure that leaves it.

1. Medical and dental, reduced on the form by 7.5% of adjusted gross income.

2. Taxes you paid, choosing income tax or sales tax but not both, then capped.

3. Interest you paid, split between what a lender reported on Form 1098 and what it did not.

4. Gifts to charity, reduced by the 0.5% floor that applies from 2026.

5. Casualty and theft losses, disaster-related only, from Form 4684.

6. Other itemized deductions, from the closed list in the instructions.

7. Total, and compare with your standard deduction. You take the larger, unless you check line 18 and deliberately take the smaller.

A hypothetical example of a full form. Nadia files as a single taxpayer with adjusted gross income of $95,000. Her costs for the year:

• Unreimbursed medical and dental expenses of $9,400. The floor is 7.5% of $95,000, which is $7,125, so the medical section carries $2,275.
• State income tax of $6,200 and real estate tax of $3,100, totaling $9,300, comfortably under the state and local cap, so all of it carries.
• Home mortgage interest of $11,800, reported to her on Form 1098.
• Cash gifts to charity of $4,000, reduced by the 0.5% floor of $475, which is 0.5% of $95,000, so $3,525 carries.
• No casualty losses and nothing on the closed list.

The total is $26,900, which is $2,275 plus $9,300 plus $11,800 plus $3,525. That figure goes to Form 1040 if it beats her standard deduction for the year, and is worth nothing at all if it does not. Notice how much of the arithmetic the form did to her rather than for her: $13,400 of medical bills and charitable gifts produced $5,800 of deductions before the comparison with the standard deduction even began.

What the form does well

• The fixed six-section layout makes it obvious which category a cost belongs in, and equally obvious when a cost belongs in none of them.
• Two of the limits are computed on the form itself, so a filer cannot forget the medical floor or the state and local cap.
• The form flags its own documentation thresholds, naming the $250 acknowledgment and the Form 8283 requirement on the page rather than burying them in a publication.
• Line 18 exists at all, which means the federal form accommodates a decision driven entirely by a state return.

Limits and cautions

• Almost every line has a limit that is applied somewhere other than Schedule A, so the numbers you enter at the top of a section are frequently not the numbers that survive.
• Line 16 reads like a catch-all and is a closed list, which is where costs that stopped being deductible in 2018 still get entered by hand.
• The form gives no hint that a cost already deducted on a business schedule or excluded from income cannot appear here, beyond one caution near the top.
• The whole exercise can produce nothing. A completed Schedule A smaller than the standard deduction changes no tax, and there is no line on the form that tells you so.