Yes you can allocate the usage of a single asset between two business. You must take care to not double-dip, taking the same expense for both businesses.
Care is needed when entering the asset on the new business. Please see the example below. Since the asset will not have been used before in the second business, you will need to enter the pre-percentage allocation adjusted basis of the computer (from business number 1) as it's 100% basis.
Since depreciation can be a very confusing topic, here's an example of what I mean using made up numbers.
Last year say you bought your computer for $1000; you use it 80% for business so you're working with $800 as your business basis (TurboTax would want the $1000 entered and would calculate the 80% usage amounts)
So your business #1 basis is $800 and say you took $50 in depreciation last year. For 2015, your actual adjusted basis would be $750 [$800 basis - $50 depreciation]. For business #1, you would change your business usage for business #1 to 70% and that's all you have to do.
For business #2, you need to enter the basis amount before you allocate the business usage but after depreciation that has already been taken. For business #2, you would enter your original basis as $950 [$1000 cost - $50 depreciation taken] and then enter your business use as 20%.
Entering the information as suggested above should result in proper depreciation for your computer without double-dipping.
