Why do we say Nineteen-Oh-Five (1905) but Two-Thousand-and-Five (2005)?

November 18th, 2015

I recently started listening to the audio book of The Wright Brothers, as narrated by the author David McCullough. I noticed that when McCullough says a year from the first decade of the 20th century, for example 1905, he pronounces it as “Nineteen five.” Colloquially, I would usually say “Nineteen-oh-five.” But then, I thought, for years in the first decade of the 21st century, I would say “two-thousand-and-five,” rather than “twenty-oh-five.”

English-at-home.com that offers this guide:

For years up until 2000, separate the four numbers into two pairs of two:
1965 = “nineteen sixty-five
1871 = “eighteen seventy-one
1999 = “nineteen ninety-nine

For the decade 2001 – 2010, you say “two thousand and —-” when speaking British English:
2001 = “two thousand and one
2009 = “two thousand and nine

However, from 2010 onwards you have a choice.
For example, 2012 can be either “two thousand and twelve” or “twenty twelve“.