Fertilidad
Your fertile window
Revisado: 4 de octubre de 2026
Solo en inglés por ahoraYou can only get pregnant during about a week of each cycle, around ovulation. Here is how the fertile window works and why any app's estimate is only a guide.
What the fertile window is
Your fertile window is the small number of days in each cycle when sex can lead to pregnancy. It depends on how long an egg and sperm can survive. After ovulation (when an ovary releases an egg), the egg lives for about 12 to 24 hours. Sperm can survive inside the body for up to 7 days after sex. So the window is about a week long: the days before ovulation and the day of ovulation itself.
When it usually falls
Ovulation usually happens about 10 to 16 days before your next period. It does not always fall in the middle of the cycle. If you have a regular 28-day cycle, you are likely to be fertile around day 14, counting the first day of bleeding as day 1. In shorter cycles the window comes earlier, and in longer cycles it comes later. Getting pregnant soon after a period is not very likely, but it can happen if you ovulate early or have a short cycle.
Signs that ovulation is near
Around ovulation, vaginal discharge (cervical mucus) often becomes clear, thin and stretchy, a bit like raw egg white. Ovulation tests can also help. They detect a sudden rise (surge) in a hormone called luteinising hormone (LH). The surge starts about 36 hours before ovulation. These signs can vary. Even in the same person, the number of days before ovulation can change from month to month.
Why any estimate is only a guide
An app can only estimate a fertile window. It cannot see what your body is doing this month. Ciclo shows an estimated fertile window, but it cannot confirm that you have ovulated and it is not a form of contraception. Even fertility awareness methods, which track several body signs every day and are learned from a trained teacher, are only about 76% effective with typical use. That means about 24 in 100 people using them get pregnant in a year.
Planning or avoiding pregnancy
If you are trying for a baby, you do not need to find the exact day. Having sex every 2 to 3 days through your cycle means sperm are likely to be there when you ovulate. If you want to avoid pregnancy, use a reliable method of contraception rather than an estimated fertile window. A doctor, nurse or sexual-health clinic can help you choose a method that suits you.
This is general information. An estimated fertile window is not contraception. For help planning or avoiding pregnancy, talk to a doctor or nurse.