eeuwjaren

Eeuwjaren is a Dutch term used in historiography and timekeeping to denote the 100-year spans that constitute centuries, as well as the calendar years that fall within those spans. The word combines eeuw (century) and jaren (years). In calendrical practice, a century is a block of 100 consecutive years.

Under the strict historical convention, the 19e eeuw runs from 1801 to 1900, the 20e eeuw from 1901 to 2000, and so forth. In more casual usage, people often refer to the 1800s or the 1900s to denote the same intervals. The year within a century is sometimes described as the year of the century, computed as ((year−1) mod 100) + 1, while the century number is floor((year−1)/100) + 1. This distinction helps clarify phrases like "in the 20e eeuw" versus "in the year 1900."

Eeuwjaren are used to organize historical data, analyze long-term trends, and describe periods in a compact form. They appear in genealogy, archaeology, history, and data analysis when events are grouped by century. Because different conventions exist for naming centuries, care is needed when interpreting sources that refer to a century by its starting year, ending year, or ordinal number.

Related concepts include centuries, time periods, and chronology.