Fertility calculator

What was the first day of your latest menstruation?

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Fertility Calculator

Fertility Calculator

Would you like to get pregnant? With our fertility calculator you can calculate your fertile window, in other words, when your ovulation occurs. When you ovulate, you are most likely to get pregnant!

Fertile window calculator

Fertile window calculator

You can increase your chance of getting pregnant when you are at your most fertile. You can use our fertility calculator to calculate your fertile window. You need to know your menstrual cycle. An average cycle lasts 28 days, with day 1 being the first day of your period. About halfway through the cycle (day 14), ovulation occurs, and you are fertile. This helpful graphic shows you your most fertile days.

Ovulation and fertility

Ovulation and fertility

Ovulation is part of your monthly cycle. Your ovulation occurs during each menstrual cycle, which is once a month. During ovulation, the mature follicle (egg vesicle) in your ovaries bursts. This releases the egg cell, which then makes is way to the fallopian tube. The egg can be fertilized up to 24 hours after ovulation. No fertilization occurs? Then the egg will dissolve and slowly your period will start.

Fertile days calculator

How do I detect ovulation?

Of course you can use our fertility calculator to determine your ovulation, but there are some symptoms of ovulation you can experience yourself:

  • Ovulation pain: ovulation is indicated by pain in the lower abdomen, also known as ovulation pain. It is somewhat like menstrual cramps, and it can feel like a stabbing pain around the fallopian tubes. This sensation may last for a few hours. Only a small percentage of woman can feel ovulation, so you may not experience it when you ovulate.
  • Raising of falling temperature: during ovulation, your temperature will drop by about half a degree, but shortly afterwards it will rise again by about half a degree. By taking your temperature several times a day, you will know when ovulation occurs. The only downside is that when you find out, ovulation has most likely already occurred, and you will already be past your most fertile stage.


  • Changed vaginal discharge: during your fertile days, you will notice a changed structure in the secretions from your cervix. During your fertile window, the cervical mucus is transparent and elastic. It feels slippery and wet. Before and after your fertile window, the mucus is creamier and stickier.
  • Tender and painful breasts: due to the change in your hormones, you may experience sore or tender breasts during ovulation.
  • Breakthrough bleeding: during ovulation, you may experience light bleeding, also known as breakthrough bleeding or ovulation bleeding. On the day of ovulation, you will lose a few drops of blood, which can cause a somewhat brownish discharge. Such breakthrough bleeding is harmless.


Tip to calculate your fertile days

If you want to become pregnant, keep track of when your ovulation occurs. There are useful apps to help you do so. If you cannot detect your ovulation yourself, you can also use ovulation tests for this purpose. This test will indicate whether you are fertile at that given moment.


What if you can’t get pregnant?

Not being able to get pregnant may have many different causes. Ovulation may not occur, the egg cell may not be able to implement properly, or there may be a condition of infertility. Usually, there is a reasonable chance of getting pregnant over the span of a year. Did you try to get pregnant over the course of a year and failed to do so, or do you feel that you cannot become pregnant? Then it makes sense to discuss it wit your GP. Your doctor will refer you to a gynecologist or fertility specialist.