By British tradition, April Fools’ pranks are considered acceptable until noon.
The custom means that a person who plays a prank after midday may be called the April fool instead. The rule is a traditional social convention rather than a law, and modern workplaces, schools and media outlets do not always follow it consistently.
Folklorists Iona and Peter Opie documented the practice in a study of British children’s traditions during the 1950s. Their research found that the noon cutoff was observed in the United Kingdom and in countries whose April Fools’ customs developed from British traditions.
April Fools’ Day itself takes place on April 1 and has no single universally accepted origin. The British noon rule should not be confused with customs elsewhere, where pranks may continue throughout the day or where a different local deadline is observed. In Scotland, related traditions historically included Huntigowk Day.