How many people will actually turn up?

Every host asks this, and most answer it wrong in the same direction. Yes is cheap to say and expensive to act on, so the number on the guest list is always the optimistic one.

A yes is not a commitment

The distance between a reply and an arrival depends on three things: what the evening costs, how well the guests know you, and how easy it is to change their mind on the day.

A free event announced to a wide group has the widest gap. A dinner someone paid for, in a small group, has almost none. Everything else sits between.

Read the replies you have

Replies arriving in one list, with the answers attached, tell you more than a count does. Someone who answered every question is coming. Someone who replied in the first hour is coming. Someone who said maybe three weeks ago and has not opened it since is not.

You do not need a model. You need to read what is in front of you.

Plan for the room, not the list

Set capacity by what the space can hold well, not by how many said yes. A room that is comfortably full at twenty is a good evening; the same room with thirty in it is a worse one, even though more people came.

If you are unsure, close registration early and open it again. It is easier to add people than to ask them to leave.