How do I deduct a truck bought for business? Also need to split cost between 2 companies if possible. Would like to spread out over a few years

You have two self-employment activities reported in TurboTax.

The expenses of a vehicle used 100% for business activity but used in two self-employment activities may be allocated between Activity 1 and Activity 2. 

If Activity 1 used 60% of the business miles and Activity 2 used 40% of the business miles, expenses related to the vehicle can be allocated on a 60%/40% basis.

In TurboTax Online, vehicle expenses may be entered by following these directions: 

• Down the left side of the screen, click on Tax Home.
• Click the down arrow to the right of Income & Expenses.
• Click on the blue band labeled Pick up where you left off.
• At the screen Your 2024 self-employed work summary, click on the pencil to the right of the self-employment activity.

• At the screen Here’s your business info, click on the pencil to the right to enter vehicle expenses.

See TurboTax Help.

The ARE sole proprietorships (Schedule C, on your personal tax return), right?  Not a Corporation or Partnership (or an LLC taxed as a Corporation or Partnership)?

Just to clarify James' response, you still enter 100% of the expenses for each business. But when you enter the business miles for each business, the program will automatically prorate the expenses based on the ratio of business miles for that business compared with the total odometer miles for the year.

However, depreciation may be a problem in this scenario.

If you use the Standard Milage Rate, everything will be fine (but you are required to use it for BOTH business, or NEITHER business; you can't use the Standard Mileage Rate for one business and not the other).

If you use Actual Expenses and use Straight-Line depreciation and NOT use Bonus Depreciation or Section 179, everything will be fine (but you need to do it the same for both businesses).

If you use Actual Expenses and try to use 200%DB accelerated deprecation, Bonus depreciation or Section 179, then reporting it under two different businesses will be a problem.  The work-around isn't particularly easy, so you may consider going to a tax professional.