Rumi calendar

The Rumi calendar (Turkish: Rumi takvim, "Roman calendar"), a specific calendar based on the Julian calendar but starting with the year of Muhammad's emigration (Hijra) in 622 AD, was officially used by the Ottoman Empire after Tanzimat (1839) and by its successor, the Republic of Turkey until 1926. It was adopted for civic matters and is a solar based calendar, assigning a date to each solar day.

In the Islamic state of the Ottoman Empire, the religious Islamic calendar was in use, within which days are numbered within each lunar phase cycle. Because the length of the lunar month is not an even fraction of the length of the tropical year, a purely lunar calendar quickly drifts relative to the seasons.

In 1677, Head Treasurer (Turkish: Baş Defterdar) Hasan Pasha under Sultan Mehmed IV proposed the correction of financial records by dropping one year (an escape year) every 33 years, resulting from the difference between the lunar Islamic calendar and the solar Julian calendar.

In 1740 (1152 AH) during the reign of Sultan Mahmud I, March was adopted as the first month of the fiscal year for the payment of taxes and dealings with government officials instead of Muharram following Treasurer Atıf Efendi's proposal.

Proposed by Treasurer Moralı Osman Efendi during the reign of Sultan Abdul Hamid I, the range of the fiscal calendar applications was extended in 1794 to state expenditures and payments in order to prevent surplus cost arising from the time difference between the Islamic and Julian calendar.

...
Wikipedia