If you own more than one business, or a business and a rental, or several rentals, the IRS treats each one as its own “activity” by default. That sounds harmless. It is not. It means hours you spend on Business A do not count toward Business B, and losses from one cannot freely offset income from another. The fix, in many cases, is a grouping election.
What "grouping" actually means
Grouping treats two or more activities as one activity for the passive activity rules. Once grouped, your hours combine, the income and loss combine, and the material participation test is applied to the whole group. If the group is non-passive, every piece is non-passive.
You can group activities together when they form what the rules call an appropriate economic unit. The standard is facts-and-circumstances, with five factors carrying the most weight: similarities between the businesses, common control, common ownership, geographic location, and interdependencies (shared customers, shared employees, one buys from or sells to the other).
The classic use case: business + rental of its building
You own a business and you own the building it operates out of. Without grouping, the rental income is “self-rental” income (non-passive), but any rental loss is passive and useless. Grouping the rental with the operating business turns the whole thing into one non-passive activity, so losses on the building flow against the business income.
A rental can be grouped with a trade or business only if (a) one is insubstantial compared to the other, or (b) each owner of the business has the same proportionate ownership in the rental. For a one-owner business renting from the same owner’s LLC, the second condition is automatically met. For a married couple who file jointly, ownership counts as one taxpayer, so the same rule applies even if one spouse owns the business and the other owns the building.
The real estate professional version
If you qualify as a real estate professional (REPS), every rental you own is still tested for material participation property by property unless you make a separate election. That election, sometimes called the “aggregation” or “single activity” election, combines all your rentals into one big activity. You only have to clear material participation once instead of fifteen times.
This election is all-or-nothing. You cannot pick and choose which rentals to include. And once made, it is binding for every future year in which you remain a qualifying real estate professional.
Disclosure: this is paperwork, not a checkbox
A grouping is not effective unless you file a written statement with your return for the year you first group. The statement names the activities, the EINs (if any), and declares that they form an appropriate economic unit. The same disclosure is required when you add a new activity, drop one out, or regroup.
If you do not file the disclosure, the default rule applies: every activity is separate. That is the most common preventable mistake in this area.
What to watch for
Once you group, you generally cannot ungroup, even if a future year would be better off split apart. You can only regroup if the original grouping was clearly inappropriate, or if facts have materially changed (a sale, a new partner, a geographic expansion). The IRS can also force a regroup if it concludes the grouping was done primarily to dodge § 469.
Grouping also affects dispositions. When you sell a single activity, suspended passive losses from that activity free up. When you sell one piece of a grouped activity, the losses do not free up the same way: they stay tied to the surviving group. That can be the right answer if it is planned for, and the wrong one if it is not.