Under current tax law, the special depreciation allowance may allow you to deduct 100% of the basis of an asset in the current year.

The special depreciation allowance can be found at the screen How much do you want to deduct for the business use of this vehicle?  At the bottom of the screen, you may select I'll take the special depreciation allowance.

In TurboTax Online Self-Employed, follow these directions to find this page.

• Down the left side, click Federal.
• Click on Income & expenses.
• Under Your income and expenses, click on Edit/Add to the right of Self-employment income.
• Click on Edit next to the business name.
• To the right of the vehicle expenses, click Edit.
• Under Vehicle Summary, click Edit to edit the entries.  Click Delete to delete the entries.
• Continue through the pages.
• At the screen Based on the miles you drove, your standard mileage deduction is, click on I'll enter my actual expenses.
• Continue through the pages to the screen How much do you want to deduct for the business use of this vehicle?  At the bottom of the screen, you may select I'll take the special depreciation allowance.

Thanks for your reply but I don't see "federal" or "income & expenses" anywhere on the screen. What I see on the left is Turbo Tax, Tax Home, Documents, on top, and on the bottom, Intuit Account, sign out. How do I get to the page where I can find "Federal," so I can then follow your instructions?

If you click Tax Home on the left, does the tax return that you have been working on appear?

Yes I found it. I went thru the instructions for Vehicle Summary to the page Ka-ching. I went thru it twice and nowhere on the screen did I find How much do you want to deduct for the business use of this vehicle? nor at the bottom I'll take the special depreciation allowance. Please help. I am being told I have to enter something here. 

At the screen You've got a standard mileage deduction, did you choose Yes, I'd like to see if my actual expenses give me a bigger deduction?

This will trigger the questions asking about computing depreciation.

Does your self-employment activity show a loss before entering vehicle expenses?  Perhaps you do not qualify for the other varieties of depreciation because you are in a loss status.   This TurboTax Help states:

Your Section 179 deduction amount can't exceed your net business income for the year.