It's important to be as accurate as possible with your final guest count so each of your vendors are properly prepared for your wedding day. As RSVPs should be due about two to four weeks prior to the wedding, you should have a decent sense of numbers around that time. Here's the scoop on who needs to know your final guest count and when they need it by.
As they'll be prepping all the food and drinks, catering will want the most accurate guest count possible. Most caterers ask for this number up to two weeks in advance of the wedding, and a deadline should be clear in their contract. If they haven't checked in for your final guest count by a week prior to the wedding, you may want to follow up with a number anyway. It's entirely likely that one or two guests may fall off the list in that final week, so just let catering know if there are any last-minute cancellations or additions.
Your wedding planner will likely be the person communicating your final guest count with all of your wedding vendors. They'll need to know the final total as soon as that RSVP date hits so they can finalize all of your details accordingly.
Even if your venue isn't handling your catering, they'll still need to know your final guest count so they can manage things on their end, including ensuring they have the proper staffing, security, electricity requirements, and restrooms. Go ahead and give them a shout with your final guest count when you hand it in to catering.
The florist really only needs to know the final number of tables at your wedding, which you may not be able to confirm until the final guest count rolls in. Be sure to keep them in the loop once you've decided the total quantity of centerpieces you'll need.
Cakes are usually ordered a few months in advance, using an estimate of the number of servings you'll need. This is usually accurate enough for the cake baker, but if you've had a significant increase or decrease in numbers, you should let them know about two weeks prior to the wedding.
Your catering company or wedding planner may be managing your rentals, in which case they would edit your order according to the final guest count. Otherwise, you should let the rental company know your final guest count about two weeks prior to the wedding.
If you've hired shuttles for your wedding, you'll want to let the company know your final guest count about five days to a week in advance. If you think you'll need additional shuttles, let the company know sooner so they don't rent out their vehicles to another party.