when to start taking OPKs?

I'm trying to figure out when to start taking OPKs....

Some months I have O'd on CD 14. Some months 18-20. One month last year I O'd on CD 29 (take about a frustrating month!).

I have eleven OPKs left, so I don't want to start too early and run out (I'll buy more if we're not successful this month... but I don't want to buy another box and waste them if we are successful this month). But I also don't want to start testing too late and not get it right.

I'm on CD 11 right now. Should I start testing today and just take the risk that I'll need to buy more or should I wait to start testing?

Thanks!

Cycle day 13 from what I read

Info on OPKs! *UPDATED 7/23/10* - OPK Help - BabyCenter

Do you get any pre O signs? I get AF like symptoms before O and will start testing then.

does your surge fade in? If it does I would suggest cd 13 if its super neg. then I would skip a day and test again on cd15. If you have a short surge I would suggest testing once a day.

I always check my cm and that gives me some idea as to when to start testing.
I don't get a lot, but when it starts getting clear-ish and less pasty.
As well, I temp. That helps. Usually when my temps stay low for a few days etc. I know o is coming.

I am pretty regular though, o-ing cd14-17. Normally on cd15. I know to start checking opk's cd13.
If I were u I would start on cd12 -- especially if you could o on cd14.
Check for other signs too.

bigchrista- I don't get any O signs. As for a surge, I use the clearblue digital testers, so it's either a smiley face or nothing.

prayforprincess- my cm is not reliable right now because of the diet, supps and rephresh. :( But I'm thinking day 12 sounds like a good idea.

Thanks!

Have you tried checking cervical position? I usually start using my OPK's when I see clear CM and my cervix is starting to soften/open. Even if you have trouble checking CP, if you check CM internally there's always some up near the cervix, enough for you to see if it's creamy or clear anyways.

I'd start testing sooner rather than later, because you can start Oing earlier on supps. If you O on CD 12, an OPK on CD 13 isn't going to help! ;)

I'd start on CD 10 - haven't seen many O's prior to that!