Zeller's Algorithm can be used to determine the day of the week for any date in the past, present or future. Actually, the algorithm works only for those dates starting with the use of the Gregorian Calendar in the year 1582. The Gregorian Calendar will be off one full day in the year 4902, so this algorithm works for any dates between 1582 and 4902.

To use this algorithm, input your date of birth as MM (for month) DD (for day) and YYYY (for year), press "OK" and the day of the week in which you were born appears.