Schedule A Line 5a: Income vs. Sales Tax, SALT Cap, and AMT

On Line 5a of Schedule A (Form 1040), you enter either the state and local income taxes you paid during the year or the state and local general sales taxes you paid, and you check the box that shows which one you chose.¹ You cannot claim both in the same year.² Whatever number you put here is then combined with real estate taxes on Line 5b and personal property taxes on Line 5c, and the total is subject to the SALT cap before landing on Line 5e.

Which Election Should You Make

For most people who live in a state with an income tax, adding up state and local income tax produces the larger deduction. The sales tax election is usually the better move if you live in a state with no income tax, or if you made an unusually large taxable purchase during the year, such as a vehicle, boat, or aircraft. Run the numbers both ways before you commit.

A “general sales tax” for this purpose means a tax charged at a single rate on a broad range of retail items.¹ Excise taxes on gasoline, alcohol, tobacco, or other specific products do not count, and neither do narrow taxes on selected services or luxury items.

Adding Up State and Local Income Tax

If you elect income taxes, pull your Form W-2s. Box 17 shows state income tax withheld and Box 19 shows local income tax withheld.³ Add those figures across every W-2. Then add any estimated state or local tax payments you made during the year, and any balance-due payment you made with your prior-year state return during this tax year. Keep confirmations or canceled checks with your records.

One trap: Form 1099-G is not proof of taxes you paid. A 1099-G reports a refund you received, which is a different issue that may affect next year’s federal return.

Calculating the Sales Tax Deduction

If you elect sales taxes, you have two ways to build the number: track actual receipts for the whole year, or use the IRS Optional Sales Tax Tables in the Schedule A instructions.⁴ Almost everyone uses the tables. The tables estimate your deduction based on income, exemptions, and the sales tax rates where you live. The IRS also publishes an online Sales Tax Deduction Calculator that runs the same math and handles mid-year moves or areas with different local rates.⁵

On top of the table amount, you can add the actual sales tax paid on certain large purchases, including motor vehicles, boats, and aircraft.⁴ Keep the receipts for those items. The table amount plus any qualifying large-purchase taxes is what goes on Line 5a.

How Line 5a Feeds the SALT Cap

Line 5a does not stand alone. It joins Line 5b (real estate taxes) and Line 5c (personal property taxes) on Line 5d, and that combined total is then capped on Line 5e.⁴

For 2026, the cap is $40,400 for single filers, married filing jointly, and head of household. Married couples filing separately get half, at $20,200 each.² That is a significant increase from the $10,000 flat cap that applied from 2018 through 2024. The One Big Beautiful Bill Act raised the cap starting in 2025 and indexes it at 1% per year through 2029.

The statutory schedule:

2025: $40,000 ($20,000 MFS)
2026: $40,400 ($20,200 MFS)
2027: $40,804 ($20,402 MFS)
2028–2029: continues increasing by 1% annually
2030 and beyond: reverts to $10,000 ($5,000 MFS) unless Congress acts

The 2030 reversion is already written into law.²

The High-Income Phase-Out

The higher cap is not available at every income level. If your modified adjusted gross income exceeds $505,000 in 2026 ($252,500 if married filing separately), the cap starts shrinking. For every dollar of MAGI above that threshold, the cap drops by 30 cents.²

Take your MAGI, subtract $505,000, multiply by 0.30, then subtract that from $40,400. The cap can never fall below $10,000 no matter how high your income runs. A single filer with $600,000 in MAGI, for example, loses $28,500 from the cap (($600,000 − $505,000) × 0.30), which leaves an allowable SALT deduction of $11,900. Around $606,334 in MAGI, the cap hits the $10,000 floor. If your income is anywhere close to the threshold, work through the State and Local Tax Deduction Worksheet in the Schedule A instructions before you write a number on Line 5e.⁴

The AMT Adds It Back

Whatever you claim on Line 5a and the rest of Line 5 is added back to your income when the Alternative Minimum Tax is calculated. Federal law specifically disallows the deduction for taxes described in Section 164(a) in computing alternative minimum taxable income.⁶

If your income puts you anywhere near AMT territory, a large SALT deduction can be part of what triggers it, and some of the tax savings you expected from itemizing may not materialize. Tax software runs Form 6251 automatically, but the mechanism is worth understanding before you file.⁷

What Happens to a State Refund Next Year

If you deduct state income taxes on Line 5a this year and then receive a state refund next year, part or all of that refund can be taxable federal income under the tax benefit rule: when you recover an amount you previously deducted, you owe tax on it to the extent the deduction actually reduced your tax.⁸

The refund is only taxable up to the amount by which your itemized deductions exceeded the standard deduction you could have taken. If you barely cleared the standard deduction, most or all of the refund is tax-free. The state will send Form 1099-G, and the Form 1040 instructions walk through the calculation.

Important exception: if you checked the sales tax box on Line 5a instead of the income tax box, none of your state income tax refund is taxable. You did not deduct those income taxes, so the tax benefit rule has nothing to recover.

Married Filing Separately

When you file separately, the SALT cap drops to $20,200 for 2026, and the phase-out threshold drops to $252,500.² There is also a rule that catches couples off guard: if one spouse itemizes, the other spouse must itemize too and cannot use the standard deduction.⁹ Both spouses will complete Schedule A and their own Line 5a even if one has almost nothing to deduct.

Each spouse only deducts the state and local taxes they individually paid. Withholding from your paycheck is yours; withholding from your spouse’s paycheck is theirs. Joint estimated state payments have to be allocated between the two returns.

Part-Year Residents and Multiple States

If you moved during the year, you can still deduct all the state income taxes you paid across every state on a single Line 5a. Add the withholding and estimated payments from each state together and enter the total.

If you go with the sales tax election, the IRS Sales Tax Deduction Calculator handles multiple residences. Enter each location, and it pro-rates by the number of days you lived there and by the applicable state and local rates.⁵

Records to Keep

Hold on to W-2s, estimated payment confirmations, and any receipts for large purchases you added to a sales tax deduction, for at least three years from the date you filed. The IRS has six years to audit if income was underreported by more than 25%, so keeping records longer is reasonable if your return is complicated.¹⁰ For the table-based portion of a sales tax deduction, no receipts are required, because the IRS is supplying the estimate.

Fixing a Line 5a Mistake After Filing

If you entered the wrong amount on Line 5a, checked the wrong election box, or realized you should have itemized instead of taking the standard deduction, file Form 1040-X to amend the return. Attach a corrected Schedule A with the updated Line 5a and explain the change in Part II of Form 1040-X.¹¹

You generally have three years from the date you filed the original return to amend. Amended returns can be e-filed for recent tax years. If the correction produces a refund, IRS processing typically takes 8 to 12 weeks.

1
Internal Revenue Service. Topic No 503, Deductible Taxes
2
Office of the Law Revision Counsel. 26 USC 164 – Taxes
3
Internal Revenue Service. About Form W-2, Wage and Tax Statement
4
Internal Revenue Service. Instructions for Schedule A Form 1040
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Internal Revenue Service. Use the Sales Tax Deduction Calculator
6
Office of the Law Revision Counsel. 26 USC 56 – Adjustments in Computing Alternative Minimum Taxable Income
7
Internal Revenue Service. Instructions for Form 6251, Alternative Minimum Tax – Individuals
8
Office of the Law Revision Counsel. 26 USC 111 – Recovery of Tax Benefit Items
9
Internal Revenue Service. Itemized Deductions, Standard Deduction
10
Internal Revenue Service. How Long Should I Keep Records
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Internal Revenue Service. Instructions for Form 1040-X