The protection period — also called a holdover, carryover, or extension period — says the brokerage is still owed its fee for some time after the agreement ends, if you buy a property they introduced you to. It exists for a fair reason: without it, a buyer could tour homes with an agent for months, let the agreement lapse, and close on one of those homes the following week with no fee owed. The clause protects real work.
Whether a particular protection period is reasonable comes down to two details: how long it runs, and what it covers.
The two details
Length varies enormously — thirty to ninety days is common; some forms run six months or a year. Coverage is the sharper detail: a period limited to properties the brokerage actually showed you, named in writing, protects their work and nothing else. A period covering any property in the market, or one with no stated list, can mean owing a fee to a brokerage you left, on a home they never touched, alongside whatever you owe the agent who actually closed it.
The interaction with your next agreement is the part almost nobody prices in: sign with a new brokerage during someone else's protection period and, depending on both documents, one purchase can trigger two fees. Different agreements handle this differently, which is exactly why the clause deserves a careful read before the first signature, when every version of it is still on the table.