How long was World War I?

World War I lasted 4 years (1914 – 1918) across 5 major phases.

Duration Overview

Duration

4 years

Start

1914 AD

End

1918 AD

Outbreak & Movement (1914) 155 days

1914 AD – 1914 AD

Assassination of Franz Ferdinand. Mobilization. Race to the Sea.

Trench Warfare Begins (1915) 1 years

1915 AD – 1915 AD

Western Front stalemates. Gallipoli. Poison gas introduced.

Attrition (1916) 1 years

1916 AD – 1916 AD

Verdun (303 days). Somme (141 days). Jutland. Millions die for miles.

Crisis & Collapse (1917) 1 years

1917 AD – 1917 AD

Russian Revolution. US enters war. French mutinies. Passchendaele.

Final Offensives (1918) 317 days

1918 AD – 1918 AD

Spring Offensive fails. Hundred Days. Armistice at 11am, November 11.

That's 4 years — about 1461 days. Short enough that people alive at the start could remember the end.

How long was World War I?

4 years, 3 months, 14 days (July 28, 1914 – November 11, 1918). 20 million dead, 21 million wounded. The war that ended empires.

When did World War I start and end?

World War I began in 1914 and ended in 1918, spanning 4 years.