Schedule A is the tax form that lets you list specific expenses—medical bills, mortgage interest, charitable donations, and more—to potentially lower your tax bill more than the standard deduction would. For 2017, understanding this form is crucial whether you're filing on time, late, or amending a previous return. Here's everything you need to know in plain English.

What the Form Is For

Schedule A (Form 1040) allows you to claim itemized deductions instead of taking the standard deduction when filing your federal income tax return. Think of it as a detailed receipt list of qualifying expenses you paid during the tax year that the IRS allows you to subtract from your income before calculating how much tax you owe.

The form is attached to your main Form 1040 and covers seven major categories of deductible expenses: medical and dental costs, taxes you paid, interest you paid, charitable gifts, casualty and theft losses, job expenses and certain miscellaneous deductions, and other itemized deductions.

You only use Schedule A if your total itemized deductions exceed your standard deduction—otherwise, you're better off taking the simpler standard deduction route.

For 2017, the standard deductions were:

• $6,350 for single filers
• $12,700 for married couples filing jointly
• $9,350 for heads of household
• $6,350 for married filing separately

If your qualifying expenses add up to more than these amounts, Schedule A can save you money.

When You’d Use It (Including Late or Amended Filings)

You would file Schedule A with your original 2017 tax return if you determined that itemizing would give you a larger deduction than the standard amount. But what if you've already filed or missed the deadline?

Late Filing

If you haven't filed your 2017 return yet (as of 2025), you're significantly late and may face penalties and interest. However, you can still file and include Schedule A if itemizing benefits you.

The IRS generally allows you to file returns up to three years past the due date to claim refunds, though penalties apply if you owe taxes.

Amended Returns

If you already filed your 2017 return using the standard deduction but later realized you could have saved more by itemizing, you can file Form 1040-X (Amended U.S. Individual Income Tax Return) within three years of the original filing deadline (generally April 15, 2018, extended to April 15, 2021, for refund claims).

When amending to switch from standard to itemized deductions, you must attach a completed Schedule A showing all your deductions.

Common Scenarios for Amended Filings

• Discovering forgotten charitable donations
• Receiving corrected mortgage interest statements (Form 1098)
• Finding medical receipts that push your total above the standard deduction

Key Rules for 2017

Several important thresholds and limitations applied specifically to tax year 2017.

Medical and Dental Expenses

You could only deduct the portion exceeding 7.5% of your adjusted gross income (AGI).
This favorable 7.5% threshold applied to all taxpayers for 2017, extended from what would normally have been a 10% floor.

State and Local Taxes (SALT)

You had to choose between deducting state and local income taxes OR general sales taxes—not both.
You could also deduct real estate taxes and personal property taxes based on value.

Home Mortgage Interest

Interest on mortgages taken out after October 13, 1987, had limitations on how much loan principal qualified for deduction.
Mortgage insurance premiums were deductible for 2017 through a special extension.

Charitable Contributions

Cash donations were generally limited to 50% of AGI, while property donations had different percentage limits depending on the type of property and recipient organization.

Miscellaneous Deductions

Unreimbursed employee expenses, tax preparation fees, and investment expenses were only deductible to the extent they exceeded 2% of your AGI.

Phase-Out for High Earners (Pease Limitation)

If your AGI exceeded certain thresholds, your total itemized deductions could be reduced.

For 2017, the phase-out began at:

• $156,900 for married filing separately
• $261,500 for single filers
• $287,650 for heads of household
• $313,800 for married filing jointly

Above these amounts, deductions were reduced by 3% of the excess over the threshold, up to a maximum reduction of 80% of certain itemized deductions.

Standard Mileage Rates for 2017

• Medical travel: 17 cents per mile
• Charitable activity: 14 cents per mile
• Business use: 53.5 cents per mile

Step-by-Step (High Level)

Here's how to approach Schedule A systematically:

Step 1: Gather Documentation

Collect all receipts, statements, and forms related to your deductible expenses:

• Medical bills and insurance statements
• Property tax bills
• Mortgage interest statements (Form 1098)
• Charitable donation receipts
• Records of other qualifying expenses

Step 2: Complete Each Section

Work through the form line by line:

• Calculate your deductible medical expenses (total minus 7.5% of AGI)
• Enter taxes you paid
• List home mortgage and investment interest
• Total your charitable contributions
• Calculate casualty and theft losses
• Add up miscellaneous deductions (minus 2% of AGI)

Step 3: Apply the Phase-Out (If Applicable)

If your AGI exceeds the thresholds mentioned earlier, use the Itemized Deductions Worksheet in the instructions to calculate any reduction to your total deductions.

Step 4: Compare to Standard Deduction

Add up your total itemized deductions and compare them to your standard deduction amount.
Use whichever is higher.

Step 5: Attach to Form 1040

Include the completed Schedule A with your tax return if you're itemizing.

💡 The IRS instructions provide detailed worksheets for complex situations like allocating taxes between multiple properties or calculating the deductible portion of charitable vehicle donations.

Common Mistakes and How to Avoid Them

Mistake #1: Forgetting the AGI Thresholds

Many taxpayers include their entire medical bill or all miscellaneous expenses, forgetting about the 7.5% and 2% AGI floors.
Always subtract the threshold first—only the excess is deductible.

Mistake #2: Double-Dipping

Don't claim expenses on both your business schedule (like Schedule C) and Schedule A.
Business expenses go on business forms; personal itemized deductions go on Schedule A.

If you claimed a self-employed health insurance deduction on Form 1040 line 29, reduce the medical insurance premiums you enter on Schedule A.

Mistake #3: Including Non-Deductible Items

Common non-deductible expenses include:

• Cosmetic surgery (unless medically necessary)
• Over-the-counter medications (except insulin)
• Homeowners association fees
• Federal income taxes

Mistake #4: Missing Required Documentation

For charitable contributions of $250 or more, you need written acknowledgment from the organization.
For non-cash donations over $500, complete Form 8283.
Without proper documentation, the IRS can disallow your deductions entirely.

Mistake #5: Deducting State Tax Refunds Incorrectly

If you received a state tax refund in 2017, don’t reduce your 2017 deduction by it.
If you itemized in the prior year, you may need to report the refund as income on Form 1040, line 10.

Mistake #6: Ignoring the Phase-Out Calculation

High-income taxpayers often miss the requirement to reduce their itemized deductions when AGI exceeds the threshold.
Always check if the Itemized Deductions Worksheet applies to you.

What Happens After You File

Once you file your Schedule A with Form 1040, the IRS processes your return and applies your itemized deductions to calculate your taxable income and final tax liability.

Processing Timeline

E-filed returns typically process within 21 days; paper returns take 6–8 weeks or longer.
The IRS may automatically correct minor math errors or obvious mistakes.

Verification and Audits

The IRS has up to three years from your filing date to audit your return.
Keep all documentation supporting your Schedule A deductions for at least three years (seven is even safer).

If selected for audit, you'll need to prove each deduction with receipts, statements, or other contemporaneous records.

Refunds or Additional Tax

If your itemized deductions resulted in a refund, you'll receive it via direct deposit or check.
If you owe additional tax, the IRS will send a notice with payment instructions.

Amended Return Consequences

If you file an amended return to switch from standard to itemized deductions, expect processing to take 8–12 weeks or longer.
The IRS will recalculate your tax and either issue an additional refund or send a bill for more tax owed plus interest.

State Tax Impact

Most states follow federal itemized deductions with modifications.
Filing Schedule A on your federal return may affect your state tax return, so you may need to amend state returns as well.

Frequently Asked Questions

Q1: Can I itemize if my spouse takes the standard deduction?

No. If you're married filing separately, both spouses must use the same method.
If one itemizes, the other must also itemize—even if the standard deduction would be better individually.

Q2: What if I paid medical expenses for my non-dependent parent?

You can include medical expenses you paid for someone who would have been your dependent except that they received $4,050 or more of gross income or filed a joint return.

Q3: Are property tax assessments for improvements deductible?

No. Assessments that increase your property's value (like new sidewalks or street lights) aren’t deductible; they're added to your home’s cost basis.
Only assessments for maintenance of existing facilities qualify.

Q4: Can I deduct both mortgage interest and real estate taxes on a rental property?

No. Expenses for rental properties go on Schedule E, not Schedule A.
Schedule A is only for personal residence expenses.

Q5: What happens if I made a large charitable donation that exceeds the AGI limit?

You can carry forward the excess contribution for up to five future tax years, subject to the same percentage limitations.

Q6: Do I need receipts for charitable donations under $250?

Yes. You need a bank record (cancelled check, credit card statement) or written communication from the charity showing the organization's name, date, and amount.

Q7: What if I paid 2018 property taxes in December 2017?

If your 2018 property taxes were assessed and paid in 2017, you could include them on your 2017 Schedule A.
They had to be both assessed and paid—not merely prepaid.

References

• 2017 Schedule A Instructions (IRS.gov)
• About Schedule A (IRS.gov)
• Publication 502 - Medical and Dental Expenses (IRS.gov)
• Publication 936 - Home Mortgage Interest Deduction (IRS.gov)