The SSTB (specified service trade or business) designation reduces or eliminates the 20% Qualified Business Income (QBI) deduction at higher income levels.
Because the official definition of an SSTB can be vague and open to interpretation, expanded definitions and examples are given below.
Keep in mind: The SSTB label is irrelevant if your 2021 total taxable income (which includes non-business as well as business income) is less than $164,900 (or $329,800 if you're filing jointly). At these lower income levels, owners of SSTB as well as non-SSTB businesses can qualify for the same QBI deduction: 20% of either taxable income (minus capital gains and dividends) or qualified business income, whichever is less.
Select a service business for more details on what constitutes an SSTB in that field: