St Patrick's Day, on which Ireland ’s patron saint is celebrated around the world, is always held on March 17, which has fallen on a Monday this year. It's not a bank holiday in the UK or a federal holiday in the US but it is a public holiday in Northern Ireland and the Republic of Ireland.

Pi Day itself dates to 1988, when physicist Larry Shaw began celebrations at the Exploratorium science museum in San Francisco. The holiday didn’t really gain national recogniti