What Schedule A (Form 1040) Is For

Schedule A (Form 1040) is the IRS form you use to claim itemized deductions on your federal income tax return. Think of it as a detailed list of certain expenses you paid during the year that the government allows you to subtract from your taxable income. The form covers specific categories of expenses, including medical and dental bills, certain taxes you paid, mortgage interest, charitable donations, and casualty or theft losses from federally declared disasters.

The fundamental question when filing taxes is whether to itemize your deductions using Schedule A or take the standard deduction. In 2018, the Tax Cuts and Jobs Act (TCJA) dramatically changed this calculation by nearly doubling the standard deduction to $12,000 for single filers, $18,000 for heads of household, and $24,000 for married couples filing jointly. This meant far fewer taxpayers benefited from itemizing—dropping from about 30% of taxpayers to roughly 10%. You should only use Schedule A if your total itemized deductions exceed your standard deduction amount, resulting in lower taxes. IRS.gov

Schedule A attaches to your Form 1040 and feeds directly into line 8 of that form, reducing your adjusted gross income to arrive at your taxable income. The lower your taxable income, the less federal tax you owe.

When You’d Use Schedule A (Form 1040)

Original Filing

You should file Schedule A with your original 2018 tax return if your itemized deductions exceed your standard deduction. The original deadline for 2018 returns was April 15, 2019 (extended to April 17, 2019, in some areas).

Late Filing

If you missed the original deadline but haven't filed yet, you can still file a late return with Schedule A attached. There's no statute of limitations on filing an original return, though you may face penalties if you owe taxes. However, to claim a refund, you must file within three years of the original due date. For 2018 returns, this meant the deadline to claim a refund was April 18, 2022—that window has now closed. IRS.gov

Amended Returns

If you already filed your 2018 return but realized you should have itemized instead of taking the standard deduction (or vice versa), you can file Form 1040-X (Amended U.S. Individual Income Tax Return) with a corrected Schedule A attached. You generally have three years from the date you filed your original return, or two years from the date you paid the tax (whichever is later), to file an amended return claiming a refund. For most 2018 returns filed by the deadline, this meant you had until April 2022 to amend.

The IRS doesn't require you to amend for simple math errors—they'll correct those automatically. However, you must file an amendment if you want to switch from standard to itemized deductions, forgot to claim significant deductions, or discovered errors in the amounts you reported. IRS.gov

Key Rules or Details for 2018

State and Local Tax (SALT) Deduction Cap

One of the most impactful changes was the $10,000 cap ($5,000 if married filing separately) on combined state and local income taxes (or sales taxes), real estate taxes, and personal property taxes. Before 2018, these deductions were unlimited, so this cap hit taxpayers in high-tax states particularly hard. IRS.gov

Mortgage Interest Limitations

For mortgages taken out after December 15, 2017, you can only deduct interest on the first $750,000 of mortgage debt ($375,000 if married filing separately) used to buy, build, or substantially improve your home. The previous limit was $1 million. Additionally, interest on home equity loans is no longer deductible unless the loan proceeds were used to buy, build, or improve your home. IRS.gov

Medical Expense Threshold

You can deduct unreimbursed medical and dental expenses only to the extent they exceed 7.5% of your adjusted gross income (AGI). This was a temporary reduction from the previous 10% threshold.

Miscellaneous Deductions Eliminated

All miscellaneous itemized deductions subject to the 2% AGI floor were suspended for 2018 through 2025. This eliminated deductions for unreimbursed employee business expenses, tax preparation fees, investment advisory fees, and safe deposit box fees. IRS.gov

Casualty and Theft Loss Restrictions

You can only deduct personal casualty and theft losses if they resulted from a federally declared disaster. Previously, you could deduct these losses regardless of whether they occurred in a disaster area.

Charitable Contribution Limits

The limitation on cash contributions to public charities increased from 50% to 60% of your AGI, encouraging more charitable giving.

Overall Limitation Removed

The "Pease limitation," which reduced itemized deductions for high-income taxpayers, was repealed for 2018 through 2025.

Step-by-Step (High Level)

Step 1: Gather Your Documentation

Collect receipts, statements, and forms related to deductible expenses: medical bills and insurance statements, property tax bills, mortgage interest statements (Form 1098), charitable donation receipts, and state/local tax records or W-2s showing tax withholding.

Step 2: Calculate Medical and Dental Expenses (Lines 1-4)

Add up all unreimbursed medical and dental expenses paid in 2018 for yourself, your spouse, and your dependents. Multiply your AGI (Form 1040, line 7) by 7.5%. Subtract this threshold from your total medical expenses. Only the amount exceeding 7.5% is deductible. If the result is zero or negative, you get no medical deduction.

Step 3: Calculate Taxes Paid (Lines 5a-5e)

You must choose between deducting state/local income taxes OR general sales taxes (not both). Most people choose income taxes. Add your state and local income taxes withheld (shown on W-2s and other forms), estimated tax payments made during 2018, and state/local taxes paid with your 2017 return. Add real estate taxes and personal property taxes (like vehicle registration fees based on value). Cap the total of lines 5a, 5b, and 5c at $10,000 ($5,000 if married filing separately).

Step 4: Calculate Interest Paid (Lines 8a-8e)

Enter mortgage interest from Form(s) 1098 that you received from your lender(s). If your mortgage debt exceeded $750,000 (or $375,000 married filing separately) for loans after December 15, 2017, you may need to calculate a reduced deduction. Enter mortgage insurance premiums if eligible (this deduction was extended retroactively). Add investment interest expense if applicable (this has separate limitations).

Step 5: Calculate Charitable Contributions (Lines 11-14)

Separate your donations into cash contributions and noncash contributions. Cash includes checks, credit cards, and payroll deductions. For noncash contributions over $500, you must also file Form 8283. Total contributions to public charities generally can't exceed 60% of your AGI for cash and 30% for noncash property.

Step 6: Calculate Casualty and Theft Losses (Line 15)

For 2018, you can only deduct losses from federally declared disasters. Use Form 4684 to calculate the deductible amount after applying the $100 per casualty floor and 10% of AGI reduction.

Step 7: Report Other Itemized Deductions (Line 16)

This line includes gambling losses (up to gambling winnings), casualty and theft losses from income-producing property, and federal estate tax on income in respect of a decedent.

Step 8: Calculate Your Total (Line 17)

Add lines 4, 5e, 6, 7, 8e, 9, 10, 14, 15, and 16. This is your total itemized deduction. Transfer this amount to Form 1040, line 8 (but only if it exceeds your standard deduction). IRS.gov

Common Mistakes and How to Avoid Them

Mistake #1: Itemizing When the Standard Deduction Is Higher

The single most common error is filing Schedule A when your itemized deductions don't exceed the standard deduction. Always calculate both and choose the larger amount. Tax software typically handles this automatically, but manual filers should compare carefully.

Mistake #2: Exceeding the $10,000 SALT Cap

Many taxpayers, especially in high-tax states, forget about the $10,000 limit and deduct the full amount of their state and local taxes. Lines 5a, 5b, and 5c combined cannot exceed $10,000 ($5,000 married filing separately). Double-check your math and don't transfer an amount greater than the limit to line 5e.

Mistake #3: Deducting Ineligible Mortgage Interest

Not all mortgage interest is deductible in 2018. Home equity loan interest is only deductible if you used the proceeds to buy, build, or substantially improve your home. Interest on loans used for other purposes (paying off credit cards, funding education, etc.) is not deductible. Many taxpayers missed this change.

Mistake #4: Missing the Medical Expense Threshold

Your medical expenses must exceed 7.5% of AGI before any become deductible. If your AGI is $50,000, the first $3,750 of medical expenses provides zero tax benefit. Only amounts above that threshold count. Many filers waste time documenting medical expenses that provide no deduction.

Mistake #5: Claiming Miscellaneous Itemized Deductions

Tax preparation fees, unreimbursed employee expenses, and investment fees are NOT deductible in 2018. These miscellaneous deductions subject to the 2% floor were suspended. Including them will trigger IRS corrections or potential audits.

Mistake #6: Inadequate Documentation

Always keep receipts, canceled checks, acknowledgment letters from charities, and Form 1098s. For charitable contributions of $250 or more, you must have written acknowledgment from the charity. For noncash donations over $500, you must file Form 8283. Missing documentation can result in disallowed deductions during an audit.

Mistake #7: Deducting Non-Disaster Casualty Losses

Personal casualty and theft losses are only deductible if they occurred in a federally declared disaster area. Losses from car accidents, pet damage, or non-disaster theft are not deductible in 2018.

What Happens After You File

Initial Processing (4-8 Weeks)

Once you file your 2018 return with Schedule A attached, the IRS processing center enters your return into their system. The IRS computer system performs automatic checks for math errors, missing Social Security numbers, and mismatched information from third-party reports (W-2s, 1099s, 1098s). Simple math errors get corrected automatically, and you'll receive a notice explaining any changes. Your refund (if any) is typically issued within 21 days for e-filed returns or 6-8 weeks for paper returns. IRS.gov

Document Matching

The IRS matches the information on your Schedule A against third-party documents. For example, they'll verify your mortgage interest claimed matches what your lender reported on Form 1098. They'll check that your state tax refund on Schedule 1 corresponds to what your state reported. Discrepancies may trigger automated notices requesting clarification or proposing adjustments.

Selection for Examination

A small percentage of returns are selected for audit. The IRS uses a computerized scoring system (Discriminant Information Function or DIF) that flags returns with unusual deductions compared to taxpayers with similar income levels. Schedule A itemizers face slightly higher audit rates than standard deduction filers, particularly for large charitable deductions, high medical expenses, or SALT deductions at the maximum limit. The audit rate for individual returns is typically less than 1%, but it increases for higher-income taxpayers. Most audits occur within two years of filing. IRS.gov

Three Types of Audits

• Correspondence Audit (most common): The IRS sends a letter requesting documentation for specific items on your Schedule A, such as charitable contributions or medical expenses. You respond by mail.
• Office Audit: You're asked to bring documents to a local IRS office for review.
• Field Audit (rare for individual returns): An IRS agent visits your home or accountant's office to examine your records.

Statute of Limitations

The IRS generally has three years from your filing date (or the due date, whichever is later) to assess additional tax. For 2018 returns filed by April 15, 2019, the statute typically runs until April 15, 2022. This period can be extended if you substantially underreported income or never filed a return.

Record Retention

Keep copies of your 2018 return, Schedule A, and all supporting documents for at least three years, or longer if you filed a claim for a loss from worthless securities or bad debt deduction. The IRS recommends keeping tax records for seven years if you claim a loss on worthless securities. IRS.gov

FAQs

1. How do I know whether to itemize or take the standard deduction?

Calculate your total itemized deductions on Schedule A and compare to your standard deduction ($12,000 single, $18,000 head of household, $24,000 married filing jointly for 2018). Choose whichever is larger. If your itemized deductions are even $1 higher than the standard deduction, itemizing saves you money. Tax preparation software makes this comparison automatically.

2. Can I deduct medical expenses my insurance reimbursed me for?

No. You can only deduct medical expenses that were not reimbursed by insurance or any other source. If you received reimbursement in 2018 for expenses paid in 2018, subtract the reimbursement from your total medical expenses before calculating your deduction. If you deducted expenses in a prior year and received reimbursement in 2018, you may need to report the reimbursement as income.

3. What if I paid my 2019 property taxes early in December 2018—can I deduct them?

This became a controversial issue after tax reform. You can only deduct property taxes that were assessed before January 1, 2019, and paid in 2018. Many localities don't assess the next year's taxes until January, so prepaying in December provided no deduction. State and local tax law determines when property taxes are "assessed," and the IRS issued guidance clarifying that prepaying 2019 taxes before they were assessed doesn't make them deductible in 2018. IRS.gov

4. Are my donations to GoFundMe or other crowdfunding campaigns deductible?

Generally, no. Charitable contributions are only deductible if made to qualified 501(c)(3) organizations. Donations to individuals, even for worthy causes, are not deductible. Contributions made through crowdfunding platforms to help specific people are considered personal gifts, not charitable donations. Only donations to the crowdfunding campaigns of qualified charities count as deductible contributions.

5. I have both a first mortgage and a home equity line of credit (HELOC). What can I deduct?

You can deduct interest on both loans, but only to the extent the total debt doesn't exceed $750,000 (for loans after December 15, 2017) and only if you used both loans to buy, build, or substantially improve your home. If you used the HELOC proceeds to pay off credit cards or buy a car, that portion of the interest is not deductible in 2018. Your lender doesn't know how you spent the money, so it's your responsibility to calculate the deductible portion. IRS.gov

6. Can I deduct my state income tax refund I received in 2018?

This is backwards—you don't deduct a refund you received. In fact, you may need to report it as income on Schedule 1, line 10, if you itemized deductions in the prior year and the deduction reduced your tax. This is called a "tax benefit recovery." If you took the standard deduction in the prior year, your state refund is not taxable.

7. What should I do if I forgot to include Schedule A when I filed my 2018 return?

File Form 1040-X (Amended U.S. Individual Income Tax Return) with your original Form 1040 and the newly completed Schedule A attached. Explain in Part III of Form 1040-X that you're switching from the standard deduction to itemized deductions. However, note that for 2018 returns, the three-year window to claim a refund has likely closed (it ended in April 2022 for timely-filed returns). If you owe additional tax instead, there's no deadline to file an amendment. IRS.gov

Key Takeaway

Schedule A (Form 1040) for 2018 reflects major changes from tax reform that dramatically reduced the number of taxpayers who benefit from itemizing. The higher standard deduction, combined with new limitations on SALT deductions, mortgage interest, and the elimination of miscellaneous deductions, means itemizing only makes sense if you have substantial deductible expenses. Always compare your total itemized deductions to your standard deduction, keep excellent records to support your claims, and be aware of the specific limitations that apply to each category of deduction. When in doubt about complex situations, consult a qualified tax professional or review the detailed instructions on IRS.gov.