When a fixed period ends the loan rolls to the lender's standard variable rate, which is almost always higher than the rate a new customer would be offered and often higher than the client expects. The lender writes to the client a few weeks before; so do competitors' marketing teams. If the broker is not in the conversation before that letter arrives, the client's next call is to whoever is.
Fixed-rate expiry is unusual among run-off causes because the date is known from settlement. A commission file records the settlement date and loan type; the fixed term is in the broker's own records. Together they produce a review calendar that can be built years in advance and that concentrates effort exactly where refinances happen.
The review itself is simple: contact the client 60 to 90 days out, obtain a rate from the current lender's retention team, compare it with the market, and either reprice or refinance before the rollover date.