Birth Control Calculator

Birth Control Methods and Effective Rates

Rhythm Method (Knaus-Ogino)Diaphragm
TypeCalendarBarrier
Perfect Use
Effective Rate*
91% effective

Out of 100 women, 91 will not get pregnant, 9 will become pregnant
95% effective

Out of 100 women, 95 will not get pregnant, 5 will become pregnant
Typical Use
Effective Rate*
75% effective

Out of 100 women, 75 will not get pregnant, 25 will become pregnant
85% effective

Out of 100 women, 85 will not get pregnant, 15 will become pregnant
Birth Control ResponsibilityFemaleFemale
Where/how do I get it--Diaphragm requires a prescription from an OB/Gyn or qualified healthcare provider.
Helps Prevent STDs No No
Hormones
None None
Permanent No No
More InfoRhythm Method CalculatorQ&A: How do I use a Diaphragm?
Rhythm Method (Knaus-Ogino)Diaphragm

*Effective rate is how well the birth control method prevents pregnancy. It is based on the percentage of 100 women per year who will not get pregnant when the birth control is used perfectly, per its instructions, or in typical use, which accounts for such common mistakes as forgetting to use (e.g. missing a daily pill) and contraceptive malfunctions (e.g. condom breaking).

Translating the effective rate to success and failure rate per person is simple. That is, approximately how many will get pregnant and how many will not? Since it's based on 100 women, the effective rate shows how many will NOT GET PREGNANT - just drop off the percentage sign! So, if a birth control is 99% effective, it means 99 will most likely not get pregnant. Then subtract that value from 100 and that's how many will likely get pregnant: in this case 100-99 = 1 woman out of 100 would get pregnant.

What do numbers like .3 women mean? For example, if the birth control is 99.7% effective, it means that 99.7 will not get pregnant, and .3 will! It basically means the 100 women is too small a sample for such a highly effective birth control. In this case, simply use a larger sample, say 1000. Then, out of 1000 women, 997 women will not get pregnant, and 3 would.

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