Yom HaZikaron’s nominal Hebrew date is 4 Iyyar, the day before Yom HaAtzmaut. Israeli law moves the observed date when that pairing would conflict with Shabbat. There is no fixed Gregorian anniversary.
Yom HaAtzmaut’s nominal Hebrew date is 5 Iyyar, the anniversary of the 14 May 1948 declaration. Israeli law moves the observed date when 5 Iyyar falls on Friday, Saturday, or Monday. There is no fixed Gregorian anniversary.