Happy New Year. I hope it's a happy and healthy year for you!
It's January 1, 2020. That means we may or may not be starting a new decade.
While it may look obvious that a new decade has begun, if we're consistent within our Gregorian calendar counting, we'll have to wait another year before that happens.
There's confusion about when decades start because Pope Gregory XIII, who in 1582 introduced the calendar most of the world uses, didn't start the calendar with year “0,” but started it with year “1.” In fact, in the Gregorian calendar, there is no year “zero.” From the year 1 BCE (formerly BC), the calendar goes to 1 CE (formerly AD).
Therefore, when a new century or millennia starts, it begins on a year that ends with a “1,” not a “0.” So, to be consistent, new decades should really start with a “1” too, but since we talk about decades belonging to teens, twenties, thirties, forties, etc., most people have gotten used to thinking decades start with the year at “0.”