A gym with capacity for a few hundred people at once will happily sell many thousands of memberships. The overselling is deliberate, and it depends on a pattern of attendance that repeats reliably.
Most members attend far less than they intend
Sign-ups are driven by intention, and attendance is driven by habit. The two diverge within weeks for a large share of new members.
People reliably overestimate how often they will attend, which is why many members on monthly terms would have paid less using a per-visit option.
The business does not need this to be true of everyone. It needs it to be true of enough people to be predictable.
The cost structure rewards volume
A gym's major costs are rent, equipment finance and staff, and all of them are fixed regardless of how many members walk in.
Each additional member who rarely attends adds revenue at almost no marginal cost, which is why membership growth improves margin far more than usage does.
This is also why the cheapest memberships are aggressively promoted, since the lowest price attracts the members least likely to attend.
Peak demand is narrow and manageable
Attendance concentrates into early mornings, evenings after work and the first weeks of January.
Operators manage those peaks with class scheduling, equipment mix and off-peak pricing rather than by limiting membership.
A location genuinely full at seven in the evening is usually near empty at eleven in the morning, and the business is sized to the average rather than the peak.
Contract design keeps inactive members enrolled
Annual commitments, automatic renewal and cancellation procedures that require notice all extend the period during which an inactive member continues paying.
Consumer protection rules in several states now regulate how these terms may be presented and how cancellation must be permitted, which has changed the practice at the margins.
The economics still rest on the gap between what members intend and what they do.
The model shapes what gyms are built
Because revenue scales with sign-ups rather than visits, operators optimise for accessibility, low price and proximity rather than for capacity.
Floor plans favour rows of identical machines that need little supervision, and staffing is kept light because most members require nothing beyond entry.
Boutique studios that charge per class invert the arrangement, since they only earn when someone attends, and their pricing, class sizes and scheduling reflect that reversal directly.