Usually we book vacation trips way ahead but we're in a position this year where we may have to book NY to FL flights on very short notice.

Is there a certain number of days in advance when fares start to go back up? In other words, assuming availability isn't a problem, will we overpay if we wait until 7 days before leaving, or 14 days, or something like that?

I'd like to book 1 week before departure but I'm concerned this will force us to pay a premium.

Generally speaking, the closer to your departure date you get,the higher the price of the ticket will be.That said, there's exceptions to the exceptions.But if you can fly schedules on Southwest (McArthur-FtLauderdale) or Jet Blue/Spirit or even Song,you should not get hit too badly.The so called low fare carriers are fairly simple fare wise.ALL of their fares are "low" or so they will tell you.And usually they are.

I will have to disagree with BeachBoi, as far as the so-called discount airlines. For the last few months, the majors, AA, DL, US, CO, UA, etc... are matching ANYTHING the discounts have on the same routes. I just checked a flight from LGA-FLL leaving next Thursday and returning the following Thursday(7 day advance), and AA came back with $155 R/T. I did not check the 'discounts', but I can't see them flying for anything less.
Best thing to do is to go to Travelocity.com, pick the airports you want, and pick flexible dates. It will come back with prices and when you choose the airline you want, it will show you the dates available.
Good Luck!

Not true AA. I just had a friend who had to fly to across the country to visit his father in the hospital. He had one day's notice and all of the majors were charging well above $1,000. JetBlue wanted $600. Yes he could have called each one of majors to see if they had a medical emergency fare, but there was no time and I doubt they would have offered him anything better than JetBlue's standard fare. The discounts do work well for last minute needs.

I find that I will not use travelocity or any of those internet travel channels on line ONLY because they only seem to show the major airline prices. They do not show Southwest, Jetblue etc.
What I do is the following (only if you have the time, like when you are sitting at work, like I am doing right now...hahaha):

1. Seach on line with travelocity etc.
2. search on line for Southwest, Jetblue etc.
3. Call up the second cheapst airfare
4. tell them the cheapest airline price and ask them to beat it.
5. Never stop with the agent on the phone. Always go to a supervisor
6. Tell the supervisor that you are a loyal customer with that airline and you would like to remain, but if they can not help you out, then you will have to take your business elsewhere.