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 left my contraceptive ring in for too long

You may forget to take your vaginal ring out at the end of week three.

If the ring has been left in for up to seven days after the end of week three (up to four weeks in total):

  • Remove your ring as soon as you remember.
  • Do not put another ring in. Start your seven day, ring-free interval.
  • After the seven days insert a new ring on the eighth day.
  • You don’t need to use additional contraception and you are protected against pregnancy.

If the ring has been left in for more than seven days after the end of week three (more than four weeks in total)

  • Remove the ring as soon as you remember
  • Insert a new ring immediately.
  • You must use additional contraception until the new ring has been in place for seven continuous days.
  • Ask your doctor or nurse for advice if you have had sex in the previous few days and were not using a condom as you may need emergency contraception to reduce the risk of an unintended pregnancy.

Emergency contraception comes in two forms, the intra-uterine device or IUD, or the so-called ‘morning after pill:

  • The IUD or copper coil is a small plastic and copper device that is fitted into the uterus through the cervix using a simple procedure that takes a few minutes. it stops an egg implanting in the uterus. IUD can be fitted up to 5 days after unprotected sex, or sometimes later depending on the usual length of your cycle. The efficacy is 99%.
  • This progesterone-only pill is a hormone pill and works by delaying the release of an egg from an ovary, therefore preventing pregnancy.The emergency contraceptive pill or ‘morning after pill’ can be taken up to 120 hours (5 days) after unprotected sex. Efficacy varies, depending on when in your cycle the sex happened. However the IUD is more effective at preventing pregnancy.

Emergency contraception is more effective the quicker you act, so if you’ve had unprotected sex, you should visit a Marie Stopes UK clinic, your GP or local sexual health centre as soon as possible.

If you want to find out whether you're pregnant, a pregnancy test will not be accurate until 2-3 weeks after the sex happened. It is advisable to take a pregnancy test after using the emergency contraceptive pill, as failure is quite common. 

You should only use emergency contraception in an emergency and not as a regular form of contraception.

Please note that as well as pregnancy, unprotected sex you 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 Central London STI clinic for testing.