USA Deducting expenses that apply to both self-employment and salary

[Jim Holloway]

i have a situation where someone has self-employment related expenses but these same expenses also apply to their job as a salaried employee. If they didn't have their salaried job, they would still need all of their licensing, certifications, insurance, etc. for their self-employment.

Is the best practice to split these costs (pro-rate or similar) between the two jobs, or is it allowable to claim them all against their self-employment income since they would have to have them regardless of their salaried job?

 

[MFox]

I've broken the cost out in the past based on income earned during year... whatever % of total income is earned under self-employment gets that % of the expense.