In the graph below you see the time zone difference between Greenwich Mean Time and Central European Summer Time. Drag the bubble to adjust the time and to see the corresponding time in the other time zone.
Greenwich Mean Time is the time zone of the 0 meridian, located in London, United Kingdom, including cities like London, Lisbon and Dublin (in the winter). Central European Summer Time is the time zone of most central European countries, and the Nordics when observing daylight saving time in the summer, with places like Paris, Berlin, Stockholm, Amsterdam, Madrid, Rome, Zurich and Warsaw.
Usually it is preferable to schedule meetings in the morning for the person in GMT and after lunch for the person in CEST.
GMT, or Greenwich Mean Time, is the zero when it comes to time zones – they are all counted from the zero meridian that runs through the village of Greenwich.
While both the UK and Portugal are officially on GMT you need to pay attention to whether they are actually observing it or are using their own. Britain in the summer for example use British Summer Time – which is different than GMT.
London, Lisbon, Dublin, Edinburgh
GMT does not observe DST as it is the zero hour time zone – it never changes.
CEST is, as the name implies, the time zone observed by Central Europe during the summer months. CEST is +2 hours ahead of UTC. Note that Portugal and the UK are not on CEST but instead observe GMT (or, in the summer BST – British Summer Time) and that Eastern Europe (every country from Finland and South) observe Eastern European Summer Time.
All countries in Western Europe, except Portugal and the UK, observe Central European Summer Time. This includes Germany, Sweden, Italy, Spain, Croatia, Montenegro and Gibraltar to name a few.
The list is long but includes Berlin, Oslo, Madrid, Rome, Tirana, Amsterdam, Paris, Warsaw, Bern, Geneva and Copenhagen.
CEST is the summer time of CET – Central European Time and is observed between the last Sunday of March and the last Sunday of October each year. The rest of the year these countries are on CET.