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 forgotten to put in a new contraceptive ring

You need to put a new contraceptive ring in at the end of the ring free interval. If you forget, insert a new ring as soon as you remember.

If you put the new ring in 48 hours or more after your ring-free interval then you may not be protected from pregnancy. Use an additional method of contraception, such as condoms, for the next seven days.

If you have had sex in the previous few days and were not using a condom, ask your doctor or nurse for advice as you may need emergency contraception to reduce the risk of an unintended pregnancy.

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:

  • 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 are 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.

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 Central London STI clinic for testing.