The megila can be read on the 11^th, 12^th, 13^th, 14^th or 15^th of Adar. Cities that were walled in the times of Yehoshua read on the 15^th of Adar. Villages and big cities read on the 14^th of Adar. Sometimes the villages can read earlier on the 11^th 12^th 13^th of Adar.

Megila 1:2

If the 14^th came out on Monday, the cities and the villages read the megila on that day and the walled cities on the next day.

If the 14^th came out on Tuesday or Wednesday, the villages read on Monday when they come anyway into the cities. The cities read on the Tuesday or Wednesday and the walled cities the day after.

If the 14^th came out on Thursday, the cities and the villages read the megila on that day and the walled cities on the next day.

If the 14^th came out on Friday, the villages read on Thursday when they come anyway into the cities. The cities read on Friday together with the walled cities.

If the 14^th came out on Shabbos, the villages and cities read on Thursday when they come anyway into the cities. The walled cities on Sunday.

If the 14^th came out on Sunday, the villages read on Thursday when they come anyway into the cities. The cities read on Sunday and the walled cities the day after.