The Calendar (New Style) Act 1750 (24 Geo. II c.23), also known as Chesterfield's Act or (in American usage) the British Calendar Act of 1751, is an Act of the Parliament of Great Britain. Its purpose was for Great Britain and the British Empire to adopt the Gregorian calendar (in effect). The Act also rectified other dating anomalies, such as changing the start of the legal year from 25 March to 1 January.