It's Aug 12-13 this year. It culminates a 3 week period of mourning and prayer but the 9 days prior from the 1st of Av to the end of the 9th of Av get really serious. Tomorrow and the next day in other words, thru to the sundown on the 13th.Tisha B'av is this month where bad things tend to happen to Israel on this feast.
Let's pray that nothing happens in terms of Israel's enemies doing anything crazy on this date