These days, people are getting less and less reliable about giving you an RSVP. If you really want guests to do it, then you have to make RSVP instructions extremely visible, provide a deadline, and say, “RSVP Required” – the less you do these things, the fewer RSVPs you will receive.
Expect to get 5-10% of your RSVPs after the deadline you set has passed. Everyone will be very apologetic.
Depending on the sort of event you are having, you should get somewhere between 25 percent and 50 percent of your RSVPs by the second Tuesday after your invitations hit mailboxes. You can use this math to tell you if you are way below target and need to do something extra to make sure you have enough attendees.
How few people warrant shutting down the event?
Honestly, there is probably no number of expected guests that is so low that you should cancel the event. Instead, when the numbers are looking low, do whatever it takes to get people there. There should be no such thing as a failed event (even if you must redefine your idea of success).
How many people warrant cutting off more people?
The flipside of having too few people is having too many. For events where people are not paying and you or a sponsor is footing the bill, you should know how many people you can afford and cut it off when RSVPs are at about 95 percent of that (yes, this means thanking people for their interest and letting them know the event is full – something anyone seldom has to do). If you are having a fundraiser, then nothing else matters except paying attendees; never turn people away, just do whatever is necessary to accommodate them.