An average woman's menstrual cycle is 28 days but cycles can range from 22 days right up to 36. Your menstrual cycle begins on the first day of your period and continues up to the day before you start your next one.
Use our free ovulation calculator to find out when you're ovulating over the next six months.
Work out your ovulation date using our tool below
Step 1: Your menstrual cycleWhen your next period starts, make a note of the date. The following month, when your period comes again, make a note of this date, then count the days in between. This will give you your cycle length. You may need to do this for more than one month and take the average, especially if your cycle isn't regular. Remember also that coming off the Pill will reveal your true menstrual cycle.
Period starts = 1st January
Next period starts = 3rd February
Days in between (including 1st Jan but not 3rd Feb) = 33 days.
Your menstrual cycle length is 33.
Step 2: Your fertile datesUsing our ovulation calender, find the right number in the menstrual cycle length column (33 for the above example) and read across for your ovulation day and most fertile days.
|Cycle length||Ovulation||Most fertile|
|22||Day 8||Days 7-9|
|23||Day 9||Days 8-10|
|24||Day 10||Days 9-11|
|25||Day 11||Days 10-12|
|26||Day 12||Days 11-13|
|27||Day 13||Days 12-14|
|28||Day 14||Days 13-15|
|29||Day 15||Days 14-16|
|30||Day 16||Days 15-17|
|31||Day 17||Days 16-18|
|32||Day 18||Days 17-19|
|33||Day 19||Days 18-20|
|34||Day 20||Days 19-21|
|35||Day 21||Days 20-22|
|36||Day 22||Days 21-23|
Step 3: Your ovulation dateWork out your ovulation and most fertile dates. For the above example:
First day of last period = 3rd February 2008
Cycle Length = 33
Ovulation (19 days later) = 22nd February 2008
Most fertile (18-20 days later) = 21st and 23rd February 2008
Once you know your ovulation date, as a rule, you are most fertile the day before, during and the day after. However, because sperm can survive for up to seven days in the right conditions you could be fertile before and after these days.
N.B These figures are based on averages and should be used as a guide only. Days and dates may differ from woman to woman.