To see the depletion field in the Q&A for a rental property you have to check the Not active participant box on the screen titled Rental Income - Active Participant.
To reach the rental income depletion screen:
From within your TaxACT return (Online or Desktop) click on the Federal Q&A tab
Click Rent or Royalty Income to expand the category, then click Real estate rental income
Click Add to create a new copy of the schedule, or click Review to edit a copy already created
Click Rental Income and continue to the screen titled Rental Income - Active Participant
Check Not active participant and click Continue
Continue through the Q&A until you reach the screen titled Rental Income - Depletion
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