Summer exams have a booking deadline (usually) in January or February.  Winter exams have deadlines around September – October.   Usually, February/March is for the summer exam series, although it will change each year slightly. Your exam centres have their deadline for accepting entries. Typically Centre’s deadline is December or early January. If you miss the deadline, boards accept late entries, all boards accept late entries – but there are late entry fees. It is still up to the exam centre whether to accept your entries. You can try another centre.