I'm going to start doing this this month (I should have taken my temperature this morning as it is the first day of my period but I didn't have one so I only bought it this afternoon). What I want to know is if this works or not because from what I've been reading, when your temperature "spikes" that is after you've ovulated which is surely too late. I know you are still fertile for 2 days (apparently) after you've ovulated but can you tell from your temperature when you are going to ovulate before it actually happens? I'm also going to use OPKs this month. Just wondering, do you use them from the first day your period ends or after about a week or so when you are likely to ovulate?