It is difficult to pin point exactly how long the British Empire lasted for a number of reasons, the first being that, technically, it still exists, as Great Britain still has overseas territories (listed below).
However, it could be argued that many of these are "British" in name only, and not governed in the same way that the colonies were.
The British Empire's origins date back to the late 15th century, with the first settlements taking place almost a hundred years later under the guidance of Elizabeth I.
After hundreds of years of power and oppression, the Empire began to decline after the second world war. Britain as a nation were essentially bankrupt, and anti-colonial movements were gaining momentum.
Most people agree that the Empire as it was finally came to an end in 1997, when Hong Kong became a special administrative region of China.