How do I calculate business-use-of-personal items such as internet use for a web based business, mobile phone use that's used for both personal and business, etc.

[RyanO-]

Would I prorate deductible expense amount and report business use only?  What documentation would support this pro-rating?

[TurboTaxTerry · Accepted solution]

One option would be to claim the expenses under the Office in Home section and prorate based on your use of the residence by rooms or square footage.

The other option is to perform reasonable calculation based on your actual use for business purposes and claim the amount as a general expense.