if you took depreciation Turbotax would have the amount. evidently, you used the standard mileage deduction which has a depreciation element each year. to calculate your depreciation you need to multiply your business mileage each year by the rate in effect for each year. the total business depreciation can not exceed the business portion of the cost of the car which you compute by taking its cost and multiplying by the total of the business mileage for each year and dividing by the total of all mileage for all years. this per-mile rate comes from IRS publication 463.
when using the standard mileage method Turbotax, and even professional tax software, does not track depreciation
2020 $0.27
2019 0.26
2017–2018 0.25
2015–2016 0.24
2014 0.22
2012–2013 0.23
what if you didn't keep records going back that far! well you should be able to go online and get IRS transcripts or request actual copies of tax returns using form 4506
https://www.irs.gov/individuals/get-transcript
https://www.irs.gov/pub/irs-pdf/f4506.pdf
