Hello @ashlea,
Georgia kindly has you covered - Yule is indeed on December 21st this year in the Northern Hemisphere. It will occur at 4:21 am EST (source). That is the moment of the Winter Solstice, when the sun reaches it’s lowest point and after which the days will begin to get longer again 
That being said, while the winter solstice itself is one brief moment in time, people tend to celebrate the occasion over many days. Have you heard of the 12 Days of Yule? Or even the 21 Days of Yule? Depending on your tradition, there are many fun ways to celebrate the days surrounding the solstice 
Whichever days you pick to add to your planner and however you choose to celebrate them, I’m wishing you a happy and blessed Yuletide. Enjoy! 