An ovulation calculator estimates a woman's fertile days in a month based on the dates of menstruation. The calculator estimates that ovulation occurs around day 14 of a 28-day cycle, explains WebMD. Ovulation may occur ... More »

The first step in using any fertility calculator based on ovulation dates is to chart the dates of your last few menstrual periods, according to WebMD. Note the date that you began menstruating on a calendar, and mark it... More »

www.reference.com Health Women's Health

Calculate how many weeks of a pregnancy have passed by beginning with the first day of the woman's last menstruation and counting forward, explains BabyCenter. Women who have been tracking their ovulation and know their ... More »

Birth control pills work by releasing hormones into a woman's body to alter her regular hormonal balance, causing the processes associated with menstruation to fail, according to TeensHealth. Without proper hormone level... More »

www.reference.com Health Women's Health Birth Control

A woman is fertile for up to one day after ovulation, per About.com. An egg is viable for 12 to 24 hours following ovulation, the American Pregnancy Association notes. After that time, unfertilized eggs then disintegrate... More »

www.reference.com Health Women's Health Birth Control

The first step in using any fertility calculator based on ovulation dates is to chart the dates of your last few menstrual periods, according to WebMD. Note the date that you began menstruating on a calendar, and mark it... More »

www.reference.com Health Women's Health

Although the Plan B pill can affect the timing of the next period after its use, it should not stop menstruation once it has started. This pill can cause menstrual flow issues at the next period after its use, states Web... More »