As a self-employed, if I charge daily per diem on my invoice for food while traveling, do I need to declare that as an income and the food as an expense?

Yes. If you are charging your clients for meal expenses, then what they pay you is income. And what you pay for the food is an expense.

If I am charging a flat rate per diem to my client, do I need actual receipts to claim the offsetting deduction for the additional income, or is my invoice showing a separate per diem amount from the service cost sufficient?

@tcdlittle You would include any amounts that you charge to your clients as income. If you want to claim expenses against this or any other income, then you would need to have receipts to show you actually made purchases or incurred fees.

Thank you for using TurboTax. 

Hi Susan,

Okay, thank you!

Terry