It was similar, but there was an intercalary month that was used to properly adjust the calender so that spring would begin at approximately the same time each year. During the events of the civil war, proper use of the intercalary month had practically ceased and the calender was so far off that no one really bothered. Once Caesar won and came to power, he introduced reforms utilizing Greek methods (probably picked up while he was in Alexandreia) to realign the calender and develop the Caesarian calender.