Hotel rates in American convention cities swing violently across a single month, and the cause is usually one event rather than general demand. The mechanism runs on contracts signed years earlier.
Room blocks are committed far ahead
Large conventions negotiate blocks across many hotels, often several years before the event. Those contracts fix a rate and a number of rooms.
The negotiated rate is typically below what the hotel could otherwise charge that week, which is the discount the city offers to win the event.
In exchange the hotel gets certainty. A block filling a difficult week is worth more than the chance of higher rates that may not materialize.
Attrition clauses transfer the risk
Blocks include attrition provisions requiring the organizer to pay if the rooms are not filled. That is what makes the hotel willing to hold inventory for years.
Organizers manage the exposure by encouraging attendees to book inside the block rather than independently, which is why registration pages push the official hotel list.
Attendees who book outside the block save the organizer nothing and can trigger those penalties, which is the real reason the messaging is so insistent.
Unsold block rooms return to market late
Blocks release unbooked rooms back to general inventory at a cutoff date, commonly a few weeks before the event.
That release produces a sudden availability spike at high rates, which is why searching a sold-out convention week sometimes finds rooms appearing without warning.
The returned rooms are priced at market, not at the block rate, so they arrive expensive rather than discounted.
Spillover reaches well beyond the venue
When downtown inventory fills, demand pushes outward to airport and suburban hotels, and rates rise there too despite having no connection to the event.
The effect reaches resorts within driving distance of the city, particularly for attendees extending a trip into a weekend.
Travelers with unrelated plans in a convention city are paying event pricing without knowing an event exists, which is the most common form of the surprise.
Checking the calendar before booking
Convention and visitor bureaus publish event calendars showing major citywide bookings, and those calendars explain rate anomalies more reliably than any deal-hunting tool.
Shifting a stay by a few days around a large event often produces a larger saving than any other adjustment available.
The same calendar works in reverse. The week following a major convention is frequently the softest of the month, as the city empties and hotels reprice to fill.