The transition from Julian to Gregorian Calendar.
Erling Poulsen    
October 15th 1582
Italy, Spain, Portugal and Catholic parts of Poland. Friday, October 15th came after Thursday, October 4th.
December 20th 1582
France and Lorraine. Monday, December 20th came after Sunday, December 9th.
January 1st 1583
Holland (Brabant, Flanders, Hennegan and some provinces to the south). Saturday, January 1st came after Friday, December 21st.
October 16th 1583
Catholic parts of Germany. At first Monday, February 21st 1583 should succeed Sunday, February 10th, but this did not work. Later it was decided that Sunday, October 16th should succeed Saturday, October 5th.
1583 and 1584
Austria
During October to December 1583.
Tyrol
Sunday, October 16th came after Saturday, October 5th.
Carinthia (Kärnten) and Styria (Steiermark)
Sunday, December 25th came after Saturday, December 14th.
Bohemia, Moravia (Mähren) and Lusatia (Lausitz)
Tuesday, January 17th 1584 came after Monday, January 6th.
Silesia (Schlesien)
Monday, January 23rd came after Sunday, January 12th.
Catholic parts of Switzerland
Sunday, January 22nd came after Saturday, January 11th.
November 1st 1587
Hungary. Sunday, November 1st came after Saturday, October 21st.
December 25th 1590
Transylvania (Siebenbürgen). Tuesday, December 25th came after Monday, December 14th.
September 2nd 1610
The duchy of Prussia. Thursday, September 2nd came after Wednesday, August 22nd.
March 1st 1700
Protestant Germany, Denmark and Norway. Monday, March 1st came after Sunday, February 18th.
1700
Holland
Gelderland
Monday, July 12th came after Sunday, June 30th.
Utrecht and Overijssel
Sunday, December 12th came after Saturday, November 30th.
Friesland and Groningen
Wednesday, January 12th 1701 came after Tuesday, December 31st.
January 12th 1701
Switzerland (Zurich, Bern, Basel, Schaffhausen, Gent, Mühlhausen and Biel). Wednesday, January 12th 1701 came after Tuesday, December 31st.
September 14th 1752
England and Scotland with colonies. Thursday, September 14th came after Wednesday, September 2nd.
March 1st 1753
Sweden. In the year 1700, it was decided to cancel the intercalary days for forty years, which was done that year, but not in 1704 and 1708, I don't know why. So until 1712, they had neither the Julian nor the Gregorian Calendar. Later, it was decided to return to the Julian Calendar by having an extra intercalary day (February 30th) in 1712. Finally, in 1753 Thursday, March 1st came after Wednesday, February 17th.
1873
Japan. Before Japan had a non-Julian calendar.
1912
China. Before China had a non-Julian calendar.
January 1st 1914
Turkey. Before, Turkey had an Islamic calendar.
February 14th 1918
Russia. Thursday, February 14th came after Wednesday, January 31st.
April 14th 1919
Romania. Monday, April 14th came after Sunday, March 31st.
March 1st 1923
Greece. Thursday, March 1st came after Wednesday, February 15th.
Number of days the Julian date is behind the Gregorian date:
1582 - 1699
10 days
1700 - 1799
11 days
1800 - 1899
12 days
1900 - 2099
13 days
2100 - 2199
14 days