Why Did September 1752 Skip 11 Days? How Britain and the American Colonies Switched to the Gregorian Calendar

If you inspect parish birth registers, colonial newspapers, or legal ledgers printed in London, Boston, or Philadelphia in the autumn of 1752, you will encounter an eleven-day gap that looks like a printing error: Wednesday, September 2, 1752 is followed the very next morning by Thursday, September 14, 1752. Nobody lost eleven days of biological life, and Earth did not speed up in its orbit. Instead, Great Britain and its American colonies were executing the Calendar (New Style) Act 1750 (24 Geo. 2. c. 23), abandoning the 1,796-year-old Julian calendar to synchronize with the Gregorian calendar already used across continental Europe.

When you calculate exact historical intervals or biographical timelines in Timeli, understanding why different countries skipped 10, 11, 12, or 13 days—and why English dates between January 1 and March 24 before 1752 carry two different years—is essential for accurate date math.

The 11-Minute-Per-Year Julian Leap-Year Error (365.25 vs. 365.2425 Days)

Why did the Julian calendar drift ahead of the seasons in the first place, and why did the number of skipped days increase from 10 days in 1582 to 11 days in 1752 and 13 days in 1918?

• Julius Caesar’s 365.2500-Day Approximation (45 BCE): The Julian calendar inserted a leap day every fourth year without exception, giving an average civil year of exactly 365.2500 days (365 days, 6 hours). However, Earth’s mean tropical year (measured between vernal equinoxes) is approximately 365.24219 days (365 days, 5 hours, 48 minutes, 45 seconds).
• 1 Day of Drift Every 128 Years: That seemingly tiny discrepancy of 11 minutes and 14 seconds per year accumulates to 1 full extra day every 128 years (or roughly 3.1 days every 400 years). By 1582, the vernal equinox had drifted 10 days backward from March 21 (its date at the First Council of Nicaea in 325 CE) to March 11.
• The Gregorian Century-Leap Filter (365.2425 Days): Pope Gregory XIII’s papal bull Inter gravissimas (February 24, 1582) dropped 3 leap days every 400 years by decreeing that century years ending in 00 (1700, 1800, 1900) are not leap years unless divisible by 400 (1600, 2000). Because the Julian calendar still treated 1700, 1800, and 1900 as leap years while the Gregorian calendar skipped them, any country that waited past February 1700 had to drop 11 days instead of 10; waiting past 1800 required dropping 12 days; and waiting past 1900 required dropping 13 days.

Global Gregorian Transition Table: From 10 Skipped Days (1582) to 13 Skipped Days (1923)

Because Protestant, Eastern Orthodox, and East Asian states adopted the Gregorian reform across four different centuries, two historical documents written on the exact same physical day in London and Paris between 1582 and 1752 bear dates 10 or 11 days apart:

“Cervantes and William Shakespeare both died on the exact same calendar date—April 23, 1616—yet they died ten days apart: Catholic Spain was already on the New Style Gregorian calendar, while Protestant England was still ten days behind on the Old Style Julian calendar.”

Why George Washington Had Two Birthdays (Old Style vs. New Style Dual Dating)

The Calendar (New Style) Act 1750 actually enacted two separate reforms across the British Empire, explaining why Old Style (O.S.) and New Style (N.S.) dates between January 1 and March 24 change both their day and their year:

1. Moving New Year’s Day from March 25 (Lady Day) to January 1 (1752): From the twelfth century through 1751, England and its colonies started the legal civil year on March 25 (the Feast of the Annunciation, or Lady Day). Thus March 24, 1750 was followed the next day by March 25, 1751! Under the 1750 Act, 1751 was shortened to a 282-day year (running from March 25, 1751 to December 31, 1751), and January 1, 1752 became the first day of the new legal year.
2. Converting Washington’s Birthday (Feb 11, 1731/32 O.S. → Feb 22, 1732 N.S.): When George Washington was born in Virginia, his family Bible recorded his birth under the Julian calendar and Lady Day year-numbering as February 11, 1731/32. After September 1752, aligning his birth date with the January 1 New Year fixed the year as 1732, and adding the 11 skipped days shifted his anniversary to February 22, 1732.
3. Why the “1752 Tax and Rent Riots” Were a Myth: Opponents later claimed that angry crowds chanted “Give us our eleven days!” out of fear that landlords would charge a full month’s rent for a 19-day September. In reality, Section 6 of the Calendar Act 1750 explicitly delayed quarterly rent, loan maturity, and tax payment dates by 11 days so that every contract ran for the exact same number of physical 24-hour days.

Calculating exact day counts between historical dates, genealogical records, or multi-century anniversaries? Open Timeli to track timelines and date spans accurately, or explore our chronology and calendar guides.