UTC, GMT, CET and CEST explained
Understand the difference between the global UTC standard, GMT, Central European Time and Central European Summer Time.
UTC
UTC (Coordinated Universal Time) is the global reference used by computer systems, aviation, science and international scheduling. UTC itself does not switch for daylight saving time.
GMT
GMT (Greenwich Mean Time) is commonly used as a time-zone label at UTC+0. In everyday clock use GMT and UTC often display the same hour, but UTC is the modern time standard.
CET
CET (Central European Time) is UTC+1 and is used as the standard-time label in many European countries during winter.
CEST
CEST (Central European Summer Time) is UTC+2 and is used during the daylight-saving period in many of those countries.
Why named zones are safer
For future appointments, use a named zone such as Europe/Copenhagen or Europe/Berlin. A fixed label like CET or UTC+1 cannot by itself tell software whether daylight saving will apply on a future date.