That's a hard one to answer because sometimes you don't lose weight but lose inches. It would depend a lot on weight loss and exercise I think. I've got a size 18 waiting in the wardrobe that I fell in love with in the Evans sale before Christmas and my friend bought it for me for Christmas. I said what if I don't get that far! She said "you've lost 3st since september , you'll get in it just carry on!"
So if you want it get it and carry on! I've gone from a 28/30 in September to a 22/24 now!
I will be wearing that dress, not sure when but definitely this year lol