The British decimal fifty pence coin (often shortened to 50p in writing and speech) is a denomination of sterling coinage worth 1⁄2 of one pound.

In 1967 the Deputy Master of the Royal Mint approached the Decimal Currency Board to ask for their advice on the introduction of a new coin.

[3] The Mint could not find a suitable metal which was sufficiently different in colour to the existing coins and which would not tarnish.

[4] A designer, Colin Lewis, suggested a much simpler shape which in its basic form is an equilateral triangle with a small circle centred on each apex and with a larger circular arc centred on each apex but tangential to each of the two opposite small circles.

(The small radius was not strictly necessary to the geometry, but made the shape more practical by removing inconvenient sharp points and reducing the rate of wear, and therefore change of size, in handling.)

The shape was drawn out by David Brown and samples made from stainless steel by the Model Shop, together with a section of perspex channel with a bend to demonstrate that the "coin" would roll around corners and drop through gauging slots.

[6] When the Decimal Currency Board met, none of the other members had any suggestion to make, so when the samples were produced the idea was accepted without opposition.

[3][4] However, there was some confusion and resistance to the new shape after its release on 14 October 1969, where the coins were mistaken for the decimal 10p and half crowns, which were both round.

Between 1985 and 1997 the portrait by Raphael Maklouf was used,[12] in which the Queen wears the George IV State Diadem.

On 3 October 2022, a commemorative 50p coin was released that was the first to carry the portrait of King Charles III following the death of Elizabeth II.

[13] The reverse of the coin, designed by Christopher Ironside, and used from 1969 to 2008, is a seated Britannia alongside a lion, holding an olive branch in her left hand and a trident in her right, accompanied by either NEW PENCE (1969–1981) or FIFTY PENCE (1982–2008) above Britannia, with the numeral 50 underneath the seated figure.

[14] The winner, announced in April 2008, was Matthew Dent, whose designs were gradually introduced into the circulating British coinage from mid-2008.