The ISO 8601 system defines weeks to prevent ambiguity. Weeks start on Monday, and week 1 of a year is the one containing the first Thursday of the year. This means some years can have 53 weeks. You can use our Week Number Calculator to find the ISO week for any date.
What Are ISO Week Numbers?
The ISO 8601 week numbering system is an international standard used to avoid ambiguity when referring to weeks of the year.
Quick Answer
ISO week numbers are an international standard for numbering weeks. In this system, a week always starts on Monday. Week number 1 of any year is always the first week that contains a Thursday. This prevents weeks from being split between two years.
Related Questions
What is UTC (Coordinated Universal Time)?
UTC is the primary time standard by which the world regulates clocks. It's the successor to GMT and is based on atomic time for precision.
What is Daylight Saving Time (DST)?
DST is the practice of advancing clocks by one hour during warmer months to extend daylight into the evening.
What does GMT stand for?
GMT stands for Greenwich Mean Time, the historic time standard based on the Prime Meridian in Greenwich, London.
What are leap seconds?
A leap second is a one-second adjustment added to UTC to keep it in sync with the Earth's irregular rotation.