Changing the previous tax year deduction calculation method in this year's filing - how?

You do not have to start over to itemize.   The software will use your standard deduction by default; but if you enter enough itemized deductions to exceed your standard deduction then the software will use your itemized deductions instead.   Your itemized deductions will go on a Schedule A.

STANDARD DEDUCTION

Many taxpayers are surprised because their itemized deductions are not having the same effect as they did on past tax returns.  The new higher standard deduction and the elimination of certain deductions, as well as the cap on state and local taxes have had a major impact since the new tax laws went into effect beginning with 2018 returns.

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 new tax laws, 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.  It is not a refund.  You will see your standard or itemized deduction amount on line 12 of your 2022 Form 1040.

2022 STANDARD DEDUCTION AMOUNTS

SINGLE $12,950  (65 or older + $1750)

MARRIED FILING SEPARATELY $12,950  (65 or older + $1750)

MARRIED FILING JOINTLY $25,900  (65 or older + $1400 per spouse)

HEAD OF HOUSEHOLD  $19,400  (65 or older +$1750)

Legally Blind + $1750

HOW TO FORCE ITEMIZED DEDUCTIONS

https://ttlc.intuit.com/questions/1900142-how-do-i-change-from-the-standard-deduction-to-itemized-or-vice-versa

https://www.forbes.com/sites/kellyphillipserb/2017/12/20/what-your-itemized-deductions-on-schedule-a-will-look-like-after-tax-reform/#629eec426334

https://ttlc.intuit.com/questions/1901530-how-does-the-itemized-deduction-differ-from-the-standard-deduction

Explain Standard Deduction—What is it?

https://ttlc.intuit.com/community/credits-and-deductions/help/what-s-my-standard-deduction/00/26370

The only place that I can think of, where it "might" make a difference, is if you received a State refund last year for your 2021 state tax return .

IF that's what you are thinking of, you can go thru the state refund questions again on the Wages & Income page  (or in Personal Taxes section if you are using H&B Desktop or SE Online versions of TurboTax).  You can reset that you used the Std Deduction last year by revisiting that menu item, and then that State refund will not be used as Federal income on the 2022 tax return. 

It may, or may not change anything, depends on whether or not you would-have maxed-out on the $10k limit for the state tax deduction last year (if you had used itemized deductions).

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