You need to take it at roughly the same time each morning (I do mine at 7am), but the important thing is to take it before you get out of bed, as any physical activity creates heat within the body.
In the first part of your cycle, as your period arrives then ceases, your BBT will drop, usually to the low 36s. As oestrogen predominates in the first part of your cycle (the "proliferative" phase, when your endometrium starts to regrow after your period), your BBTs will be generally low; but there will be daily variation. Theoretically you get a "dip" just prior to ovulation, and then a rise in BBT the following morning. In the second phase of your cycle (the "luteal" phase, named due to the presence of the corpus luteum which is the "covering" from which the ovum is released), there is a predominence of progesterone, which causes your BBTs to rise to a higher level (usually higher 36s). At 6-8 DPO (days post-ovulation) if fertilisation has occurred, there can be a "dip" in your BBT for 1 day (the so-called "implantation dip")...this may or may not signify implantation of the fertilised egg into your endometrium. I can explain why, but it gets a bit technical!
So, you should see two "phases" on your BBT chart...initially lower BBTs, then post-ovulation, higher BBTs (the so-called "thermal" shift).
There is ALOT of variation between women, and you may not have a "textbook" chart. The reason we do it is because over 3-4 cycles, it usually demonstrates a pattern which is "normal" for YOU. You can generally (not always) see when you have ovulated in retrospect, once your BBTs have risen. Use this information for the next cycle, and keep having sex around that time until you get a sustained BBT rise.
Also, I suggest charting your cervical mucus. If it is clear, and stretches when rubbed between 2 fingers, it is the so-called "egg-white cervical mucus" (EWCM)...this is the most fertile cervical fluid, and great time to have sex.
Also, OPKs are very useful too. After your first OPK becomes positive, you will generally ovulate within 24-36 hours. Don't wait...start having sex as soon as it becomes positive. Include this on your chart too.
I hope this helps. I will post my lastest chart to illustrate some of the above points. I am CD24.
Have to go, feel free to ask more questions/clarifications!
Great info J thanks!!!
J your chart looks great!!! very promising dip at 7 (?) dpo. Is that usual for you?
Thanks so much J will c how it goes this month
Pregnant for the first-time?
Not sure where to start? We can help!
Our Insider Programs for pregnancy first-timers will lead you step-by-step through the 14 Pregnancy Must Dos!