Most occupancy plans aren't wrong because the math is bad. The formula — headcount times square-feet-per-person, plus some percentage for common space — is simple enough that almost nobody gets the arithmetic wrong. They're wrong because the assumptions baked into that formula were already stale by the time the space got built out, and nobody revisited them.
A few places this shows up consistently.
The most common mistake is sizing space to the org chart on the day the lease gets signed, rather than the org chart eighteen to thirty-six months out — which is usually closer to when the space is actually delivered and stabilized after a build-out. The opposite mistake happens too: overbuilding against an optimistic growth story that stalls, leaving a tenant paying rent on space sized for a headcount that never showed up. Neither error is really about the math. Both come from treating a moment-in-time headcount number as if it were a stable input.
A blended square-feet-per-employee figure hides more than it reveals. Engineering, sales, and executive space don't compress the same way, and the mix of those departments shifts as a company matures — usually toward more collaborative and support space per person, not less, even as individual desk footprints shrink. Layer in a hybrid work pattern that's still settling into whatever it's going to be for a given company, and a single density assumption from a pro forma built two years ago is often doing a lot of unexamined work.
Conference rooms, phone booths, informal collaboration space, storage, IT closets — none of this scales cleanly with headcount, and it's the category most likely to get compressed in an early space plan to make the numbers pencil. It's also the category employees notice missing first, and the one most expensive to retrofit once the space is built.
Reorgs happen. New teams get stood up. Contractor and consultant headcount spikes around specific initiatives and then recedes. An occupancy plan with zero flex or swing space treats the org chart as a fixed target instead of what it actually is — a moving one, on a lease term that doesn't move at all.
None of this is an argument for building in more space "just in case." Over-provisioning has its own cost, and dead rent on unused square footage is exactly the kind of thing a board asks pointed questions about at the next budget review. The point isn't more space — it's being deliberate about which assumptions the plan is actually resting on, and which of those are likely to be wrong in a specific, predictable direction by the time the space is in use.
If you're mid-planning and want a second set of eyes on where your assumptions might be stale, that's a conversation I'm glad to have before the space plan is locked, not after.
— Sach
