In 1752 the American Colonies switched from the Julian Calendar to the Gregorian Calendar which required an 11-day elimination in the date. Therefore, Wednesday, September 2, 1752 was immediately followed by Thursday, September 14, 1752. Many people used both the Julian date and the new Gregorian date on documents to avoid confusion until everyone was adjusted to the change. While their consideration makes it easier for the genealogist to adjust dates on documents, it raises a question about calculated birth dates from newspaper death notices and tombstones.

Tombstones and newspapers often give the date of the death and the age of the individual rather than a birth date. Traditionally we can calculate the birth date by subtracting the given age from the death date. However, when doing this calculation for someone born before 1752 and dying after 1752 it gets more complicated. Does the age on the tombstone reflect the actual days lived or is there an 11-day error caused by the tombstone cutter subtracting the birth date from the death date to get the age? If the stone cutter or obit writer did not adjust his figures to accommodate the Gregorian Calendar introduction in 1752, the age given is wrong. Sadly, there is no way for the genealogist to know if the figures were adjusted or not.

In most cases the error is not important since the individual's name and birth date are unique to his birth place. However, if you are trying to sort out 6 Henry Neff's, all born in the same county about the same time, the 11-day error can become important.

The original calendar had 365 days in every year, in spite of the fact that a year is actually 365.24 days long. After a few centuries of using this calendar the winter holidays were falling in the summer. In 46 BC Julius Caesar developed his own calendar which corrected much of this error. He added an extra day to every fourth year to account for the previously overlooked 0.24 day per year. This adjustment still was not good enough since the Julian Calendar made the year 365.25 days which was slightly longer than the actual 365.24 days.

Further improvement to the Julian Calendar was made in 1583 by Pope Gregory XIII who declared that only millennial years that are evenly divisible by 400 would have a leap day added. Thus 1900 was not a leap year, but 2000 is and the new Gregorian Calendar was extremely accurate (but still not perfect, it is off by 26 seconds per year).

There was great opposition to using to the Gregorian Calendar because it required the date advancement. Since most people were tenants rather than land owners, they believed they would be cheated out of their rent because the next due date came 11 days earlier the following month. European countries slowly changed from the Julian Calendar to the Gregorian Calendar over the following centuries with England and the American Colonies finally changing in 1752.