Turbo Tax is giving you the 40,000max but you only add up 39,355? So you are $645 short? What are you adding? You could be missing some taxes from W2 box 14 or 19 or car registration fees.
IRS Schedule A
https://www.irs.gov/pub/irs-pdf/f1040sa.pdf
See 1040 Schedule A instructions for line 5
https://www.irs.gov/pub/irs-pdf/i1040sca.pdf
SALT State and local taxes
See line 5a page 3 Includes……
-any state withholding from your paychecks, retirement checks, unemployment checks, etc.
-a state tax due (for any year) you paid last year
-any state estimated tax payments you made during year including an overpayment applied from last year
-any local taxes withheld on your checks like SDI in box 14 or 19 on your W2
Also
State and local real estate property taxes. See line 5b page 6
State and local personal property taxes. See line 5c page 6
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