What You Are Actually Signing
Most caterers set a final count deadline somewhere between five and ten days before the event. The exact window exists because of supply chains, not bureaucracy: the kitchen orders protein in quantity on a specific delivery schedule, and the staffing rota is written once the cover number is known. Miss that window and you are disrupting someone else's procurement, not just their spreadsheet.
When you give that number, you are committing to a minimum charge. If seventeen people drop out the week before, the cost does not fall by seventeen portions — it falls by however many the caterer can still cancel, which is often zero. The number you give is a floor, not an estimate.
Additions after the deadline work differently. Most caterers will absorb one or two late additions if the kitchen has headroom, usually at a premium rate and only up to whatever ceiling the venue's cover limit allows. There is no symmetry: the count can quietly grow a little, but it almost never meaningfully shrinks.
This is why the gap between accepted and arrived matters so much in the days before the deadline. If your accepted count is ninety-two but your realistic expectation is eighty-seven, you need to decide which number to give — and understand exactly what you are paying for in either case. Submitting ninety-two protects you against surprise arrivals; submitting eighty-seven saves money but leaves no margin.
Children and suppliers catch people out here too: a child who needs a meal and a photographer who has been promised dinner are both covers the kitchen must plan for, and both are easy to forget when you are focused on the guest list.
The practical discipline is to set your own internal deadline two days before the caterer's deadline. That buffer gives you time to chase the last handful of non-respondents and reconcile the meal choices before the number hardens. Once it hardens, it is a contract. Knowing that in advance is cheaper than discovering it afterward.