I keep track of my purchases, but I don’t have a super hard, can’t-be-broke line for each month – though I do have a rough estimate for each quarter and try to be 20% under that. For me, I try to buy only as much as I think I can reasonably handle reviewing and try not to get TOO ahead of myself, because I am inevitably behind. For others, I recommend adding big sale dates to your calendar (e.g. F&F sales) and would try to spend less before those sales so I could take advantage of them and get more for my money. The other thing to do is check your stash, shop it, and don’t be afraid to mix shades and products you own – if you don’t use tinted moisturizer all the time and just need something once or twice a month, why not add a little foundation to your moisturizer?