Question for (adults) in a serious/long-term relationship (but not married)?

How do you know when your anniversary is (to celebrate it)? I have been with my boyfriend now for almost a year, but there is no "day" that pinpoints our anniversary. We just kinda met, started dating and fell in love, and the rest is history. I would really like to celebrate our 1 year anniversary though. For those of you who are in the same boat, how/when do you guys celebrate your anniversary?