The aim of the article is to study the rules of counting the seven-day week cycles during the period of Ancient Rus (XI–XVI centuries.) and the analysis of Easter elements used in the Novgorod chronicle (based on database „Chronology of the Novgorod Сhronicles IX–XV centuries“). The authors come to the following conclusions. First, Russian chronicles are full of Easter chronological elements which allow conducting reconstruction of the weeks counting systems used in Ancient Rus. Second, it was possible to reconstruct two such systems. Third, the initial reference point for calculation of the seven- day week cycles was to determine the date of Orthodox Easter. From it calculation was carried out in different directions: 1) from the start of the new church year to Easter; 2) the calculation of the week cycles from Easter to Troitsa. As an initial point of reference different reference points of the church year could be used — Troitsa, Peter’s fast, Christmas fast, Phillipp’s fast, etc., which allowed conducting a relative counting of time. Finally, the presence of Easter elements allows not only reconstructing the old dates of the modern system of counting time, but also the old Russian time counting systems.