Look for IRS guidance on the 20% pass-through deduction to be issued soon. The rules will most likely come out in proposed form. Don’t expect brevity. The new tax law allows self-employeds and individual owners of pass-through entities, such as partnerships and S corporations, to deduct 20% of qualified business income. The statute is complex, with lots of limitations, exceptions and undefined terms. Among the many issues that tax pros hope to see addressed in guidance: Definition of a qualified trade or business. The scope of specified service fields that are subject to the high-earner limitation. How to deal with tiered entities. The extent that real-property rental income reported on Schedule E of the 1040 is qualified business income. Also, whether similar activities can be aggregated.