How many weeks in advance should I write the RSVP deadline?

It depends. When is your final count due to your caterer? I'd set the deadline about a week before that. That way you'll have extra time to track down the people who don't RSVP

We are a month ahead because we need counts 3 weeks in advance.

I believe it's 2-3 weeks in advance.

I suppose a month in advance is appropriate.

I would set the date for a week or two before you have to give final numbers to your caterer. It depends on how much free time you will have to contact the non-responders.

We asked for 3 weeks before, but in hindsight, we should have asked for 4. The decor/florist company needed the number of centerpieces and chair covers 4 weeks before and the venue needed the number of tablecloths 4 weeks before. The final meal count was due the week of.

Luckily, we heard from all but 2 guests 10 days before our due date (online responses, through our wedding website).

P.S. Also, our heavily discounted hotel, room block rooms (our venue was a hotel) ran out 4 weeks before the wedding, so the procrastinators were S.O.L.

Our venue requires a final number 30 days before the wedding. But there's sooo many other things that revolve around your final guest count, that I really didn't want to wait until the last minute to do. Seating chart, escort cards, favors (if you're doing those), plus everything Dreamer mentioned. So I asked for them back August 15th, and I'll be sending them out in late May/early June, rather than July to try and get a head start.

Depends on your venue and caterer, but month seems reasonable.

I did a month.

I am asking for ours back by July 25th for a September 3rd wedding.

We are doing about 6 weeks. Our wedding coordinator told us to do 2 weeks before the room block is up in case anyone forgets to reserve on time.

I set it for a month before. I have to give our venue the final count a week before but I wanted time to follow up with anyone who didn't RSVP by the deadline. I also want to have a couple weeks to make the seating charts and get my table numbers/escort cards ordered and delivered from Minted.

1-2 weeks before your headcount is due to venue/caterer. Gives you time to track people down that didn't RSVP.

I set mine 2 weeks before my final numbers were due. This allows me time to follow-up with guests who haven't responded.

I did three weeks in advance and wish I would've done four.