Leap year checker

Because century years must be divisible by 400 to be leap years, and 2100 ÷ 400 = 5.25. February 2100 will have 28 days, and there will be no leap year between 2096 and 2104. The same rule made 1700, 1800 and 1900 common years, while 1600 and 2000 were leap years. The next century leap year is 2400.

The year of the seasons, the tropical year, is about 365.2422 days, so a 365-day calendar would slip by almost a day every 4 years and about 24 days a century. The Julian calendar's leap day every fourth year overcorrected by about 11 minutes a year; by 1582 the March equinox had drifted 10 days, which the Gregorian reform removed and the century rule prevents from recurring.

Pope Gregory XIII decreed it in the bull Inter gravissimas of 24 February 1582. Italy, Spain, Portugal and Poland switched that October, when 4 October was followed by 15 October. Britain and its colonies changed in September 1752, dropping 11 days; Russia in February 1918, dropping 13; and Greece in 1923, also dropping 13.

2028. The leap years after it are 2032 and 2036, and 29 February falls on a Tuesday in 2028, a Sunday in 2032 and a Friday in 2036. Every year divisible by 4 up to 2096 is a leap year, because the first century year in that run that fails the 400 test is 2100.

A precisão depende dos dados inseridos e das hipóteses do método. O cálculo decimal usa 50 algarismos significativos, mas estimativas, métodos numéricos e dados de origem podem ter menor precisão; o arredondamento exibido não elimina essas limitações. Exemplos resolvidos verificados com fontes independentes: 5. Por exemplo, “2024” é verificado com Python calendar.isleap(2024) = True.

Pope Gregory XIII, Inter gravissimas (1582) — the Gregorian leap-year rule; US Naval Observatory — Leap years.