十进制日（英语：Decimal Day）是指在1971年2月15日时，英国和爱尔兰政府决定将自己的货币改采十进制。

• The Royal Mint, All Change: 25th Anniversary of Decimal Currency in Britain (pamphlet distributed with 1996 Royal Mint silver proof sets)

On 15 February 1971, known as Decimal Day, the United Kingdom and Ireland decimalised their currencies.

Under the old currency of pounds, shillings and pence, the pound was made up of 240 pence (denoted by the letter d for Latin denarius and now referred to as "old pence"), with 12 pence in a shilling and 20 shillings (denoted by s for Latin solidus) in a pound.