There is no exact date specified in Quran so all the Islamic countries try to find it in 21st, 23rd, 25th, 27th and 29th. This date depends on the moon. You never know when is it going to be every year :) until the day comes and Islamic Scholars tell people that the Night of Qadr is today.
However, many Shia Muslims celebrate it in 23th every year as many Sunni Muslims celebrate it during 27th.
I go by google :)