Self employed

Your trade-in is a taxable event since you can no longer treat it as a like-kind exchange; you have to treat the transaction as a sale and a purchase. Therefore, you need to report the vehicle you traded in as the sale of business property.

When you use the standard mileage rate, depreciation is a part of the actual per mile rate.  The portion of the business standard mileage rate that is treated as depreciation will be 27 cents per mile for 2020, 1 cent more than 2019, one of the few amounts that is increasing.

Here is how -- Edit your Vehicle, and indicate you 'stopped using it for business' on x/x/2020 (screenshot).  TurboTax will ask questions about ownership, other vehicles, business mileage in 2020, etc.

Since you traded in the vehicle, you could enter $0 as a sales price, and subtract the amount of trade-in you received from the new vehicle's basis when you enter it as a Business Asset.  

Or, you could report the Sales Price as the trade-in amount, and set up the new vehicle with a cost basis of what you paid for it. 

When entering these amounts use the % of Business Use as your entries.

If you have been claiming Standard Mileage for your business mileage, depreciation is included in the deduction. 

Here's how to calculate the Standard Mileage Depreciation Equivalent (use the same amount for 'Basis for gain/loss' and 'Basis for AMT gain/loss'):

"Depreciation equivalent for total miles is a small portion of depreciation that is included (by default) when using standard mileage rate for your business car.  When you take standard mileage rate while deducting your business car miles, you must account for 'depreciation equivalent' when disposing of that car.