Why do we call this century as 21st century and not 20th century even though its the 2000s?

1. Counting Centuries: Centuries are counted from the year 1 CE (Common Era). The 1st century includes the years 1 to 100.
2. Subsequent Centuries:

- The 2nd century includes the years 101 to 200.

- The 20th century includes the years 1901 to 2000.

- The 21st century includes the years 2001 to 2100.
3. Reasoning: The year 2000 is the last year of the 20th century, and the year 2001 begins the 21st century. Thus, the 21st century covers the years 2001 through 2100.

Supplemental Knowledge:

Naming centuries follows an established convention, though at first this may appear confusing. A century is defined as being 100 years long; starting from 1 AD (Anno Domini) the century numbers begin at one and continue counting up; so for instance in this first century AD 1 through 100 are included while during subsequent ones they increase by one each decade until reaching 200 and so forth. Therefore, each new century begins and ends on years ending in "00." For example:
- The 1st century: 1 AD to 100 AD
- The 2nd century: 101 AD to 200 AD
- The 20th century: 1901 AD to 2000 AD
- The 21st century: 2001 AD to 2100 AD

Thus, even though we are currently in the years beginning with "20xx," we are in the 21st century because it started in the year 2001.

Everyday Examples:

As we celebrate birthdays, when one turns one year old they have completed one year and begun the next. At 2000 we completed one century and started another.

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