Per the IRS issues standard mileage rates for 2021 webpage:
It is important to note that under the Tax Cuts and Jobs Act, taxpayers cannot claim a miscellaneous itemized deduction for unreimbursed employee travel expenses. Taxpayers also cannot claim a deduction for moving expenses, unless they are members of the Armed Forces on active duty moving under orders to a permanent change of station. For more details see Moving Expenses for Members of the Armed Forces.
Taxpayers always have the option of calculating the actual costs of using their vehicle rather than using the standard mileage rates.
Taxpayers can use the standard mileage rate but must opt to use it in the first year the car is available for business use. Then, in later years, they can choose either the standard mileage rate or actual expenses. Leased vehicles must use the standard mileage rate method for the entire lease period (including renewals) if the standard mileage rate is chosen.
A taxpayer may not use the business standard mileage rate for a vehicle after using any depreciation method under the Modified Accelerated Cost Recovery System (MACRS) or after claiming a Section 179 deduction for that vehicle. In addition, the business standard mileage rate cannot be used for any vehicle used for hire or for more than four vehicles used simultaneously.
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the webpage or document at the time it is accessed.