Where were you last Pluterday? is a serio-comic science fiction novel by Paul van Herck, originally released in Dutch in 1968 as Sam, of de Pluterdag by J.M. Meulenhoff (in their science fiction and fantasy range M=SF as the 14th book of the range) and released in English by DAW books in 1973.

The novel won the first prize at the European Science Fiction Convention (EuroCon)^[2] in Trieste, Italy.

The theme in the book is Pluterday, an extra day in the week which can be withdrawn if one saves enough time (e.g. by taking a plane instead of a train). Only the rich can save enough time and thus Pluterday is in practice reserved for the "happy few", resulting in a class society. The existence of Pluterdays is kept secret from non-privileged people.

• Spanish (Mexico: Novaro, 1975: translated by Manuel Campo as ¿Dónde Estabas el Pasado Pluterday?)
• Swedish (Stockholm/Bromma: Delta, 1976: translated by Gunnar Gällmo as Vi ses på plurdag, ISBN 91-7228-092-1)
• French (Paris: Librairie des Champs-Elysées, 1977: translated by Mary Rosenthal as Crésudi dernier ?, ISBN 2-7024-0602-5)
• German (München: Heyne Verlag, 1981: translated by Ronald M. Hahn as Framstag Sam, ISBN 3-453-30695-3)
• Hungarian (Budapest: Háttér Lap- és Könyvkiado, 1991: translated by Anikó Kocsis as Viszlát jövő plutónap!, ISBN 963-7455-17-5)

• Where were you last Pluterday? at Goodreads