Let's answer this question slowly: Did the Eastern Orthodox Church and the Byzantine Empire ever use the same calendar?

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Eastern Orthodox Church used the Byzantine calendar from c. 691 to 1728. The Byzantine Empire used the Byzantine calendar from c. 988 to 1453. So the answer is yes.