There is no particular day for it. It just falls on whichever day is April 1st for that year.
the 1st of April
You can do something funny, just don't destroy any property, break the rules/law, or be mean/rude. It is okay if you choose to not do anything special that day.
it was made by geremany
April Fools' Day in 2011 is on Friday, April 1.