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It also prepares your body for pregnancy each month. A cycle is counted from the first day of 1 period to the first day of the next period. The average menstrual cycle is 28 days long. Cycles can range anywhere from 21 to 35 days in adults and from 21 to 45 days in young teens. The rise and fall of levels of hormones during the month control the menstrual cycle For most women, the length of time between ovulation (when an egg is released from the ovary) and their monthly period is between 12 to 16 days (this is called the luteal phase). The first day of your menstrual cycle is the first day of your period (day 1). The period usually then lasts anything from 3 to 7 days. You’ll probably find that if you get any period pains, they’ll be at their worst in the first few days of your period. Your period The menstrual cycle is an average of 28 days, although it is normal to vary between 23 and 35 days. The cycle is counted from the first day of your period. Ovulation is the release of the egg from the ovary. This usually occurs at about day 14 of the cycle. Once released, the egg is fertile for up to 48 hours. If the egg is not fertilized, then the lining of the uterus will disintegrate, causing a period. By knowing your menstrual cycle, it is possible to approximate when you will be most fertile Ovulation is the release of a single, mature egg from a follicle that developed in the ovary. It usually occurs regularly, around day 14 of a 28-day menstrual cycle. Once released, the egg is capable of being fertilized for 12 to 48 hours before it begins to disintegrate. This is the most fertile period of your cycle: during ovulation your chances of conception are highest. The time of ovulation within the menstrual cycle is determined by the luteal phase, which is usually 12 to 16 days long. You can calculate the time of ovulation within your cycle by subtracting the length of your luteal phase from the length of your cycle. For example, if your cycle is 28 days long and your luteal phase is 12 days long, the ovulation will occur on day 16 of your cycle (28-12=16) Tracking Ovulation: A woman’s monthly cycle is measured from the first day of her menstrual period until the first day of her next period. On average, a woman’s cycle normally is between 28-32 days, but some women may have much shorter or much longer cycles. Ovulation can be calculated by starting with the first day of the last menstrual period (LMP) or by calculating 12-16 days from the next expected period. The second half of the cycle is called the luteal phase and is from the day of ovulation until the next period begins. The luteal phase has a more precise timeline and usually is only 12-16 days from the day of ovulation. This ultimately means that the day of ovulation will determine how long your cycle is 1 Work out the length of your average menstrual cycle. 2  Day one is the first day of the menstrual period and the last day is the day before the next period begins. 3  Ovulation happens about two weeks before the next expected period. 4  So if your average menstrual cycle is 28 days, you ovulate around day 14. 1 Day one is the first day of the menstrual period and the last day is the day before the next period begins. 2  Ovulation happens about two weeks before the next expected period. 3 The day of ovulation differs from woman to woman and can even be different from month to month for an individual woman. For a woman with a 28 day cycle, the window of ovulation is day 11 through day 21 of your cycle. Ovulation could occur on any one day during this window. It's difficult to pinpoint exactly when ovulation happens, unless you're practising fertility awareness (FPA guide to natural family planning). However, ovulation usually happens 10-16 days before the start of a woman's next period. The menstrual cycle is counted from the first day of a woman’s period. This is day one. Some time after her period she will ovulate, then 10-16 days after this she will have her next period. 
http://www.womenshealth.gov/publications/our-publications/fact-sheet/menstruation.html http://uk.clearblue.com/menstrual-cycles-and-ovulation http://www.estronaut.com/a/menstruation_ovulation_fertility.htm http://www.ovulation-calendar.com/hlp-d01-ovulation-basics.html http://americanpregnancy.org/getting-pregnant/understanding-ovulation/ http://yourfertility.org.au/for-women/timing-and-conception http://americanpregnancy.org/getting-pregnant/ovulation-faq/ http://www.nhs.uk/Livewell/menstrualcycle/Pages/WhencanIgetpregnant.aspx
ovulation usually occurs on day _____ of a woman's cycle