How long is a decade? Meaning, Length, Formula

How long is a decade

A decade is described as a period of 10 years. According to formal definitions, the word “decade” is a translation of the Greek word “decas,” which indicates “a group of ten.”

The Romans commonly used the prefix “dec” to refer to sets of items that add up to 10, such as the decagon (a regular 10-sided polygon) or the decathlon (an athletic event consisting of ten events).

Other categories of time derived from Latin include century and millennium, which are 100 and 1000 years respectively.

Moreover, decades have made it easier to identify specific past events. For example, in the 30s or 40s, or in the 1930s and 1940s, respectively.

Each decade has a familiar name derived from important events that occurred during that period.

For example, in the history of the United States (USA) there is an event known as the “Roaring Twenties”, which refers to the period of the 1920s when many changes took place and economic growth improved.

Today, many historical events are grouped by decades. These groupings made it easier for people to see different events that happened at specific times in previous years.

How long is a decade?

Technically, a decade is a group of ten years. The word “decade” is used to describe periods according to the tens digit of the calendar year. For example, “1980s” refers to the period from 1980 to 1989, which is equivalent to a decade.

Historically, 1 Anno Domini (AD) marks the beginning of the Gregorian calendar (note that there is no year zero in the Gregorian calendar); therefore the first decade of the Gregorian calendar depicts the period between AD 0–1, while the second decade is called the period between AD 10–11.

While the nineties (90s) refers to the years between 1990 and 1999 AD, the 200th decade refers to the period from 1991 to 2000 AD.

Any event that repeats every ten years is called a ten-year event. Similarly, events occurring every 100 and 1000 years are considered centenary and millennium events, respectively.

For example, the census is conducted by the US government every ten years, that is, every ten years. In addition, many meetings are held every ten years in high schools and colleges.

Note that a decade is just a made-up name for a specific period in the calendar, equivalent to 10 years.

According to the Gregorian calendar, terms are divided into years:

  • 1 millennium = 10 centuries = 1000 years
  • 1 century = 10 decades = 100 years.
  • 1 decade = 10 years = 3652 days.


Any period of ten years is a “decade”. For instance, regardless of the calendar years covered, the statement “during his last decade, Mozart explored chromatic harmony to a unique degree for that time” solely applies to the last ten years of Wolfgang Amadeus Mozart’s life. In addition, the “first decade” of a person’s life begins from the day of his birth and ends at the end of the 10th year of life, when he turns 10 years old; the second decade of life begins with the 11th year of life (during which it is usually called “10”) and ends at the end of his life, the 20th year of life when he is 20 years old; similar to how the third decade of life begins from the 21st year of life and so on with succeeding decades of life when a person is 20 or 20 years old.

The formula for calculating a decade

The calculation of the decade formula is based on two dimensions or two perspectives, one of which means that the new decade starts with a year (the year must have a zero as the last digit) and ends with a year with nine as the last digital number too.

The same applies to the 21st century; take the 2000s for example, a decade that started in 2000 and ended in 2009.

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