Under pre-Act law, taxpayers could deduct from their taxable income as an itemized deduction several types of taxes paid at the state and local level, including real and personal property taxes, income taxes, and/or sales taxes.

New law. For tax years beginning after Dec. 31, 2017 and before Jan. 1, 2026, subject to the exception described below, State, local, and foreign property taxes, and State and local sales taxes, are deductible only when paid or accrued in carrying on a trade or business or an activity described in Code Sec. 212 (generally, for the production of income). State and local income, war profits, and excess profits are not allowable as a deduction.

However, a taxpayer may claim an itemized deduction of up to $10,000 ($5,000 for a married taxpayer filing a separate return) for the aggregate of (i) State and local property taxes not paid or accrued in carrying on a trade or business or activity described in Code Sec. 212; and (ii) State and local income, war profits, and excess profits taxes (or sales taxes in lieu of income, etc. taxes) paid or accrued in the tax year. Foreign real property taxes may not be deducted.

Prepayment provision. For tax years beginning after Dec. 31, 2016, in the case of an amount paid in a tax year beginning before Jan. 1, 2018 with respect to a State or local income tax imposed for a tax year beginning after Dec. 31, 2017, the payment will be treated as paid on the last day of the tax year for which such tax is so imposed for purposes of applying the above limits. In other words, a taxpayer who, in 2017, pays an income tax that is imposed for a tax year after 2017, can't claim an itemized deduction in 2017 for that prepaid income tax.