A professional caterer will give you advice based on their experience of portion sizes needed to cater for your guests but it is always wise to over cater rather than under cater. Depending on the length of your event, your guests might eat more than usual. Also take into account travelling guests, they will be famished by the time the food is served.
Many people attending formal events often skip meals if they know they are being served a 3 course meal. Over catering to a degree is always a good idea as the last thing you want is to run out of food. Caterers usually prepare the food off site and deliver it to your event, so the option to prepare more portions will not be possible. You shouldn’t have to worry about wasting the food, as there are many organizations including old age homes and orphanages who would greatly appreciate a food donation. Speak to your caterer about this as they often deal with such donations.
As a host of hostess there is nothing more stressful than the kitchen informing you that the food has run out. It can put a damper on the event, and if it is a paid event even more so. Proper planing is essential. For paid and large events, I strongly advise hiring an event planner to take care of these crucial elements as they have so much experience.
Happy Party Planning!