Decade has another year to go yet.
That is open for debate.
The folks on CNBC today referred to today as "the last trading day of the decade" several times.
I looked it up, and actually there are two ways to do it.
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There are two methods of counting decades in recognition. One, called ordinal, counts decades starting with the first year 1 CE (For example, the years 1981–1990 is referred to as the 199th decade), while the other, called cardinal, groups years based on having the same digits (For example, the years 1980–1989 is referred to as the 1980s, or commonly known as the eighties).
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But, you are in the minority.
A YouGov poll was conducted on December 2, 2019, asking 13,582 Americans whether the following decade would begin on New Year's Day 2020 or New Year's Day 2021.
Results show that 64% of Americans answered the next decade will begin on January 1, 2020, and will end on December 31, 2029. 19% of the Americans surveyed replied they are unsure, while 17% answered the next decade will begin on January 1, 2021, and will end on December 31, 2030.
https://today.yougov.com/topics/politics/survey-results/daily/2019/12/02/6529e/1