Gestation Calculator

This calculator has been designed to give you an idea of the treatment options available to you*. If you decide to have an abortion with Marie Stopes UK, one of our nurses will give a more approximate gestation date during your appointment by way of a scan.
*Please note that this online calculator will only give you an estimated gestation based on the details you have provided.

Please select the first day of your last menstrual period.



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I’ve missed taking a progesterone-only pill

If you miss taking one of your progesterone-only pills, this reduces how well they work at preventing pregnancy.

What to do if you've missed a pill

If you are more than three hours late taking your pill, (12 hours if you are taking POPs containing the hormone desogestrel):

  • Take a pill as soon as you remember. If you have missed more than one, only take one.
  • Take your next pill at the usual time. This may mean taking two pills in one day. This is not harmful.
  • You are not protected against pregnancy. Continue to take your pills as usual, but use an additional method of contraception, such as condoms, for the next two days.

If you are less than three hours late (12 hours if you are taking POPs containing the hormone desogestrel):

  • Take a pill as soon as you remember, and take the next one at the usual time. You are protected from pregnancy.
  • If you have missed taking one of your combined or progesterone only pills, and had sex, you may be at risk of pregnancy. You can still reduce the risk of an unintended pregnancy by using emergency contraception methods.

Emergency contraception is only available for women or girls and comes in two forms, the intra-uterine device or IUD, or the so-called ‘morning after pill’.

Please note that as well as pregnancy, unprotected sex puts you at risk of sexually transmitted infections (STIs) such as chlamydia. You should visit your local genito-urinary medicine clinic (GUM clinic) or Marie Stopes STI clinic for testing.