From the U.S. Holocaust Memorial Museum:
The internationally recognized date for Holocaust Remembrance Day corresponds to the 27th day of Nisan on the Hebrew calendar. It marks the anniversary of the Warsaw Ghetto Uprising. In Hebrew, Holocaust Remembrance Day is called Yom Hashoah. When the actual date of Yom Hashoah falls on a Friday, the state of Israel observes Yom Hashoah on the preceding Thursday. When it falls on a Sunday, Yom Hashoah is observed on the following Monday.
It falls on Monday, April 24th in 2017.
You might be interested in The Best Sites For Learning About The Holocaust.