In connection with the Carolingian renewal of education Charlemagne also cared for a homogeneous reckoning of time. He organized the Carolingian reform of the calender with the help of Alkuin of York, an Anglo‐Saxon scholar. Having heard of Alkuin's learning and teaching abilities, the Frankish King invited him to lead his Palace school at Aachen. Moving to Francia 782, Alkuin became the key counselour of Charlemagne for science, education and church matters.Among other subjects Alkuin taught the King especially calendrical reckoning (...) (computus) and astronomy, in which he took a special personal interest. Charlemagne discussed these subjects often with Alkuin, sometimes even in letters, still preserved today. For this correspondence on astronomy and calendrical reckoning it was assumed that Alkuin was the author of four short anonymous writings on computus. Moreover, Charlemagne comissioned Alkuin to write a standard work on computus, which is lost today. But three Carolingian manuals on computus survived.Which of the four anonymous writings really stem from Alkuin himself? What influence he had upon the manuals? These two questions are investigated here on the basis of the most important matter of computus: the calculation of the age of the moon in the 19‐year lunar cycle, necessary for dating the movable feast of Easter (on the first Sunday after the first full moon in spring). These facts were discussed in detail, even vehemently, in the correspondence between Alkuin and Charlemagne. (shrink)