The date of Henry IV's birth has proved problematic for two key reasons. The failure of any contemporary chronicler to note the date is one. Another is the assumption that medieval people assigned their birthdays to a specific calendar date. This note argues that Henry IV was born on a moveable feast – Maundy Thursday 1367 – and celebrated his birthday accordingly. In addition, it suggests that the origin of the custom of the sovereign's age-related donations, on Maundy Thursday, lies in Henry's own attempt to draw attention to the fact that he, like Richard II, was born on a religious feast day.