April
April.Jan: 1- 31Feb: 31-59 or 60March: 90 or 91April: 121 or 122
In regular years, the 100th day of the year is the 10th of April. In leap years, it's the 9th of April.
The 100th day of the year varies depending on whether it is a leap year or a non-leap year. In a non-leap year, the 100th day is April 10, while in a leap year, it falls on April 9. This calculation is based on the cumulative days in each month leading up to that point in the year.
December Some regions begin school in early to mid August (this gives them extra days to buffer against days off for heavy snow fall), for them day 100 may be in late November. However for most schools starting in late August or early September, the 100th day of the school year will fall somewhere in December.
Pope Valentine (Valentinus) was the 100th pope and ruled for one month in the year 827.
In the year 2016, the month of Abib fell in the month of April.
In the year 2016, the month of Nisan fell in the month of April.
Centenary means the 100th anniversay, which would be the 100th year.
September
During a year that is not a leap year it is April 10. For leap years it is April 9.
The 100th day of the calendar year, starting from January 1, is April 10. In a standard year, January has 31 days, February has 28 days, March has 31 days, and the first 10 days of April total to 100 days. In a leap year, the 100th day would still fall on April 10.
During a year that is not a leap year it is April 10. For leap years it is April 9.