How do I figure out my active duty pay deduction?

[Hal_Al]

There is no federal deduction.  

If you are asking about a state deduction, it usually comes up, automatically,  in the state interview.  For more specific advice, you'll need to identify the state.

[Carl]

What makes your AD pay deductible? There's nothing about it that would be deductible on a federal return unless you served overseas in a declared combat zone. If your state taxes personal income then it "might" be excluded from taxation by your state HOR if you qualify. But you don't say what state or provide any other clarity.