Friday the 13th is considered an unlucky day in Western superstition. It occurs when the 13th day of the month in the Gregorian calendar falls on a Friday, which happens at least once every year but can occur up to three times in the same year, for example in 2015, on 13 Feb, 13 March and 13 October. In 2017, it occurred twice, on 13 January and 13 October. In 2018, it also occurred twice, on 13 April and 13 July. There will be two Friday the 13ths every year until 2020; 2021 and 2022 will have just one occurrence each.