When does a new decade start

A new decade starts on January 1st of a year that is a multiple of 10. For example:

• The 2010s started on January 1, 2010, and ended on December 31, 2019.
• The 2020s started on January 1, 2020, and will end on December 31, 2029.
• The 2030s will start on January 1, 2030, and will end on December 31, 2039.

This is because the concept of a decade is based on the Gregorian calendar, which divides time into units of 10 years. Each decade is a period of 10 years, and the first year of a decade is always a year that is a multiple of 10.

It's worth noting that some people may use different definitions of a decade, such as a period of 11 years or a period of 12 years, but the most common definition is a period of 10 years.