you can enter your date into the knot checklist and it will tell you the exact date to send them out, but I think typically 4-5 months unless it's around a holiday or on an odd day then 7-9 months
we did ours at about 5.5 - 6 months (but then again, we only had a 7 month engagement) - I think it was a good time frame - early enough that all the OOT people who wanted to come could find cheap plane tickets, but not so early that people forget about it...
Warning
No formatter is installed for the format bbhtml
I think you can send them out up to a year if you are having a destination wedding or if a majority of the guests will be from out of town. The location of my venue is very expensive and the town on the outskirts have reasonable hotels but they book up like 3 months in ahead.
We sent ours at 8 months, but anytime in a 6 - 9 mth time frame is fine. Some of my friends have sent earlier ... like, enclosed them in Christmas cards sent in early December for their mid-September wedding. So you're fine, really, whenever.
Re: Save the Dates
www.tiffandshel.com/wedding