Quoting: ''Bottom line: The second of two July 2015 full moons falls today, on July 31, 2015. By popular acclaim, the second full moon to occur in a single calendar month is known as a blue moon. Thanks to what is called the Metonic cycle, 19 years from now, in 2034, we’ll again have another Blue Moon in July. And 19 years after that, there will be another one, in July, 2053.''
Not sure where you live, but in China it's the 31st!