Adoption of the Gregorian calendar the Empire (except Scotland, which had already done so from 1600) changed the start of the civil year from 5 April to 1 January. Consequently, the custom of dual dating (giving a date in both old and new styles) can refer to the Julian/Gregorian calendar change, or to the start of year change, or to both. The British tax year traditionally began on Lady Day (25 March) on the Julian calendar and thus became 5 April, which was the "Old Style" equivalent. A 12th skipped Julian leap day in 1800 changed its start to 6 April. It was not changed
Adoption of the Gregorian calendar old style calendar remains used in religious contexts. Today, the Gregorian calendar is the world's most widely used civil calendar. During and for some time after the change between systems, it has been common to use the terms "Old Style" and "New Style" when giving dates, to indicate which calendar was used to reckon them. The Gregorian calendar was decreed in 1582 by the papal bull "Inter gravissimas" by Pope Gregory XIII, to correct a divergence in the canonical date of the [northern] spring equinox from observed reality (due to an error in the Julian system) that affected the calculation