To you, does the new decade start in 2020 or 2021?

I always felt the 60’s were 1960–1969.
I also understand the logic of the millennium starting at 2001.

2020.

I’d say 2020.

2020.

I think I worried about that more than I should have 20 years ago until I let it sink in that it’s all arbitrary. I’ll yell “hooray” for 2020, then again for 2021.

My Jewish friends will party like it’s 5780, my Muslim friends like it’s 1441.

And yes, it’s always debatable! :-)

New Year’s Day, 2021.

“The Twenties” start in 21 days, not in a year from now. Same as @filmfann and the Sixties.

Keith Richards was asked if Altamont marked the end of the Sixties. He replied, “well, it was December of 1969, so yes, it was the end of the Sixties.”

We all got the change of millennium stuff in 1999, but nobody was making a huge deal on December 31, 2000 other than Newman.

The last day of the 10th year closes a decade.
0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
That’s ten years.
2020, January 1st, a new decade starts.

I think a decade is ANY ten-year period.

And we talk of decades as “the 60’s”. The 60’s are a decade, and 1960 is in it, while 1970 is not. The 1920s started in 1920. The 2020’s will start in 2020.

If someone is interested in counting decades from year 1 and saying 2021 is the first year in the 202nd decade since then, great. They’re right too.

So is someone born in 1995 saying the third decade of their life starts on their birthday in 2015. Though they might also say they were born in the decade of the 1990s’ and the fourth decade (meaning common parlance decades) they’ll be experiencing will begin in 2020 (or in 2021 if they mean Naval Observatory decades).

Whether people tend to be clear about what they mean when they talk about decades, is another matter.

The question is ill-formed for exactly the reasons that @Zaku points out. A new decade is starting every moment, and when any particular decade starts is not debatable once the proper frame of reference has been applied. So the 20s will always start in XX20, and the X02nd decade will always start in X021.

Historians say a “decade” ( the above digression notwithstanding) starts with the number that ends with a zero. In this case 2020.

I have 2020 vision!
If anyone tells you otherwise, poke them in the eye then point & laugh!

2020

@josie “Historians say a ‘decade’ [...] starts with the number that ends with a zero.”

Who are these “historians” you speak of? Because I work with literally a dozen historians, and none of them are willing to endorse such a blanket statement.

The only definition of “the decade” that has any significance for me is that which has the most cultural salience, i.e. a decade as defined by the last two digits of the year. So “the decade” begins in 2020.