why is TurboTax not allowing sales tax deduction on Major Purchases

Sales tax is an itemized deduction.   If you do not have enough other itemized deductions like mortgage interest, medical expenses, charity donations, etc., to exceed your standard deduction, sales tax will have no effect on your tax due or refund.

Your itemized deductions have to be more than your standard deduction before you will see a change in your tax owed or tax refund.  The deductions you enter do not necessarily count “dollar for dollar;” many of them are subject to meeting  tough thresholds—medical expenses, for example, must meet a threshold that is pretty hard to reach. (Only the amount that is MORE than 7.5% of your AGI counts)   The software program uses all the IRS rules that apply to the expenses you enter, and it tells you if you have enough to use your itemized deductions or if using the standard deduction is more advantageous for you.  Under the tax laws that have been in effect since 2018, some deductions have been capped—there is a $10,000 limit to the itemized deductions for state, local, property and sales taxes.

Your standard deduction lowers your taxable income. The standard deduction makes some of your income “tax free.”  It is not a refund.  You will see your standard or itemized deduction amount on line 12 of your 2024 Form 1040.

2024 STANDARD DEDUCTION AMOUNTS

SINGLE $14,600    (65 or older/legally blind + $1950)

MARRIED FILING SEPARATELY            $14,600    (65 or older/legally blind + $1550)

MARRIED FILING JOINTLY $29,200    (65 or older/legally blind + $1550)

HEAD OF HOUSEHOLD $21,900    (65 or older/legally blind + $1950)