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.



We are here to support you 24 hours a day, 7 days a week

Call us now on 0345 300 8090 or email services@mariestopes.org.uk

0345 300 8090

You are here

What medicines might affect my contraception?

There are some medicines that can affect how your combined pill, patch, ring, progesterone-only pill or implant works. Be aware of them.

They are as follows.

  • Phenytoin
  • Phenobarbital
  • Primidone
  • Carbamazepine
  • Rifampicin
  • Oxycarbazepine
  • Topiramate
  • Felbamate
  • Griseofulvin
  • HIV medication
  • St. John’s Wort - a herbal rememdy

If you're only taking one of these tablets for a short while, you need to have stopped it for a minimum of 28 days for your contraceptive method to be effective. You can still reduce the risk of an unplanned pregnancy by using emergency contraception methods.