What Is a Decade?

April 12, 2025 | Learning Center

A decade consists of 10 years. The term originates from the Greek word dekas, meaning “a group of ten.” In both everyday language and formal usage, a decade refers to any continuous period of ten years. Its applications span historical analysis, demographic studies, cultural commentary, and financial planning.

Understanding the Term “Decade”

The word “decade” is most commonly used to group years into ten-year periods. These periods can begin at any point but are often aligned with calendar decades (e.g., 1990–1999). In historical contexts, the term may also refer to ordinal decades within a century, such as “the second decade of the 21st century” (2010–2019).

How to Write Decades

• Abbreviations:
  The 1990s → ’90s (apostrophe replaces “19”)
  The 2000s → 2000s or ’00s (less common)
• Formal writing: Use 1980s, not 1980’s.
• Casual writing: In popular culture, descriptive labels like The Roaring Twenties or The Swinging Sixties are common. Don’t use these in formal writing.

Calendar Decades vs. Ordinal Decades

• Calendar Decade: Begins with a year ending in 0, ends in 9 (e.g., 1990–1999).
• Ordinal Decade: Begins with a year ending in 1, ends in 0 (e.g., 1991–2000), consistent with how we officially count centuries and millennia.

Notable Decade Terminology

• 1920s – The Roaring Twenties
• 1930s – The Great Depression era
• 1940s – World War II and post-war recovery
• 1960s – The Swinging Sixties
• 1980s – Pop culture boom and global tension
• 2000s – Also called the aughts or noughties in UK English

Related Words

• Decadal (adj.): Of or relating to a decade, e.g., decadal trends
• Half-decade: A five-year span
• Decennium: A rare synonym for “decade” (from Latin)

Why Decades Matter

Grouping periods of time helps us organise events and makes it easier to analyse trends, societal shifts, economic patterns, and generational identities. By studying developments in ten-year intervals, historians, researchers, and the public gain structured insight into change and continuity.

Conclusion

Whether you’re discussing “the 1980s,” referencing “the early ’90s,” or evaluating “decadal data,” understanding how decades work—along with how to abbreviate them—helps you produce clear and precise writing and analysis. Need help getting your decades lined up? Our editors are experts at helping you get your ducks—ahem, decades—in a row; you can place an order directly on our orders page. For more on units of time, see our tutorial on writing about centuries.