How can I discuss catering before the guest count is confirmed?

You are welcome to enquire before the number of guests is final. Tell us what you can about three things: your current estimate, the likely range of variation, and when you expect to know more.
The number used for an initial discussion and the number for which you formally place an order can be considered separately. It is important, however, to check the deadlines and conditions for changes before ordering.
Give a range and explain what it is based on
Rather than saying only “40 guests”, it is more informative to say, for example, “We have invited 40 people; 28 have accepted so far, and we expect around 30–35 in the end.” This is an example of how to describe the situation during a consultation.
Separate confirmed attendees from those whose replies are still outstanding, and explain the basis of your estimate. If members of your own team will also eat, say whether they are included in the count to avoid misunderstandings.
Discuss when the numbers will be known
If you have set an RSVP deadline or an internal confirmation date, share it. If not, first ask when you need to provide the final guest count.
The relevant dates include not just the event itself, but also the arrangements for ingredients, staff and tableware. Rather than assuming numbers can change until the day, agree before ordering what needs to be confirmed and when.
A change in numbers affects more than the food
Guest numbers affect drinks, tableware, service staff and the venue layout as well as food quantities. If more guests will attend, for instance, we also check whether there is sufficient space around the buffet and where people collect their glasses.
Please contact us when a change becomes known. Depending on its timing and nature, additional charges or cancellation fees may apply. Reducing the guest count does not necessarily reduce the total by the same proportion, so review the formal quotation together with the conditions for changes.
At HKG, we distinguish estimates from confirmed arrangements
You can speak with HKG before the guest count or venue is decided. We first ask about the purpose of the event and the expected attendance, then establish the number on which to base our planning for food and service.
If numbers change, we check the implications for food, drinks, staff and equipment and explain them to you. We work with the organiser to agree on the assumptions, confirmation dates and conditions for changes.
There is no need to force an uncertain headcount into a single figure. Start with your current estimate and when you expect the replies to be in.