A regular menstrual cycle is around 28-30 days. Ovulation occurs once a month – between day 12 and day 16 from the start of your period. After ovulation, an egg lives for 12 to 24 hours and it needs to be fertilised during this time. Sperm can survive up to five days while your egg survives for one day, this means that the fertile window is considered to be six days – five days before ovulation and the day of ovulation.

Use the calendar to help calculate your fertile window and when you are likely to ovulate.

Tracking your cycle can help with fertility. Enter the first day of your last period and how long your cycle usually lasts (between 20 and 45 days). We'll show you the best days to have sex that could lead to pregnancy – so you can mark your calendar.