there are lots of books on the subject. Natural family planning can be very effective IF you do it correctly which involves taking your temperature early in the morning at the same time everyday and charting the results, checking the consistency of your cervical mucous, and the position of your cervix. I don't know all that much about it because I've never done it, it may involve more, you must study how NFP works and be diligent about practicing it. It basiclly teaches you how to predict oveulation, you MUST not try to do this just by counting days in you cycle as your cycle can change every month The "Calender Method" is not safe bith control and is not the same thing as NFP or the FAM method. I would recomend talking to an OB/GYN about birth control options. I don't know if Im allowed to tell you to go to web sites or not so this may get edited out but the Planned Parenthood web site is a good resource for accurate information.
i am 5 months pregnant, when they did my first ultrasound and measured my baby, they said i was a week farther along than they thought...because i probably ovulated earlier that month, my peroids were always consistant. i wouldnt use this as your only way of birth control...or you WILL end up pregnant, you can become pregnant even on non-fertile days, maybe the chances are slimmer but the risk will always be there if you dont use birth control, you will become pregnant
MusicElle is correct. FAM can be an effective means of birth control, but only if you do it correctly and consistently, not to mention, you need to chart your cycles (basal body temps) for a couple cycles to get the hang of it beforehand. A good book on the subject is "Taking Charge of Your Fertility". FAM is not the same as the calendar method, and for me, I never took chances; we used condoms from cycle day 3 onwards until I was 100% sure I had ovulated that month (confirmed by an obvious 3 day rise in basal body temperature and the dry-up of my cervical mucus). FAM was very effective for me; I used it 9 or 10 cycles to avoid pregnancy. Then, when we started trying to conceive, I got pregnant on the 2nd cycle trying since I knew from charting that I tended to ovulate from cycle day 11 to cycle day 18.
BUT...I have a feeling this is more work than you are willing to undertake. You have to be diligent about it, and my husband and I were not opposed to an "oops" if it happened.
As far as the calendar method of birth control, it does not work. Period.
If you want effective birth control, use condoms or get on the pill.