The Old Assyrian private archives witness two different ways of measuring the time. The Old Assyrian calendar, based on a solar year and lunar months is already well-known, but it is quite recently that the beginning of the year has been fixed. In Aššur, years were name after eponyms (limum). Over the last fifteen years, seven tablets containing lists of Aššur eponyms have been identified and published as Kültepe Eponym Lists (KEL). They give the succession of the eponyms – except for a gap –, covering the end of the 20th, the 19th and 18th centuries BC. An intercalary month (Zibibirum) was added in some years to adjust the calendar to the agricultural cycle, or the last month of the year was sometimes doubled without changing its name. A recent publication suggests a possible reconstruction of the years which have contained an additional month. The Old Assyrian calendar has the peculiarity of using the word hamuštum, which is usually translated as «week». However, the number of days included in a hamuštum is still debated. In Anatolia, loan contracts are not always dated according to the Old Assyrian calendar but can use as dates important events linked to the local ruler or his family, religious festivals or agricultural activities. This contribution gives an up to date synthesis of both system of computing time attested in the Old Assyrian sources.