Save The Dates with RSVP's?

I wouldn't say so as a formal thing. However, I wouldn't have a problem with a Save The Date that was followed up by a message to 1. check we'd received it and 2. see if we had already made plans.

I suspect those who know they are on holiday etc will inform you upon receipt of a Save The Date.

I didn't send Save The Dates. I sent my invitations out in two waves, in order to account for declines and subsequent alternative invitations.

I think I'd just send your invitations out a bit earlier than the norm.

We actually did do what you're suggesting but that's because we got married abroad. We invited around 100 guests and we could have had 10 or 100 positive replies, so we needed to know this before booking the venue.

Generally speaking though, Save the Dates aren't formal.

I've not heard of it before but don't really see a problem with it.

How far in advance are you planning sending your STD? I'd be cautious of people saying they will be there and then nearer the time for whatever reason them not being able to make it.

Wouldn't it just to be easier to send you invites in different batches with the evening invites last ? then you can upgrade anyone when you get declines .

My cousin sent out her first lot of invites with an early RSVP date to those she thought might have to decline for one reason or another, then sent out the next lot with a later RSVP with some people upgraded from the evening list, then evening invites went to who ever was left and it all worked out fine.