Calendar

Calendar is a topic where questions are asked about finding the day of a particular date, finding the day after a certain number of days, or identifying odd days. It is a logical topic that uses a few simple rules and formulas.

Basic Concepts:

Ordinary Year:

• An ordinary year has 365 days
• 365 = 52 weeks + 1 day
• So an ordinary year has 1 odd day

Leap Year:

• A leap year has 366 days
• 366 = 52 weeks + 2 days
• So a leap year has 2 odd days

How to identify a Leap Year:

• A year divisible by 4 is a leap year (e.g. 2024)
• But a century year (100, 200, 300...) must be divisible by 400 to be a leap year
• 2000 = leap year (divisible by 400)
• 1900 = not a leap year (divisible by 100 but not 400)
• 2100 = not a leap year

Odd Days Concept:

Odd days are the days remaining after complete weeks.

Day Coding:

Types of Calendar Questions in SSC CGL:

Type 1 - Finding Day After Certain Number of Days

Example: If today is Monday, what day will it be after 100 days?

Solution: 

100 ÷ 7 = 14 weeks + 2 odd days 

Monday + 2 days = Wednesday

Answer: Wednesday

Type 2 - Same Calendar Year Which year will have the same calendar as a given year?

Rules:

• After an ordinary year, the next same calendar comes after 6 or 11 years
• After a leap year, the next same calendar comes after 28 years

Example: 

Year 2001 (ordinary) - same calendar in 2007 (after 6 years)

Type 3 - Finding Day of a Given Date A specific date is given and you have to find what day it was.

Method - Zeller's Rule (simplified for SSC):

Step 1 - Find the number of odd days from a reference point 

Step 2 - Reference: 1 January 0001 was Monday (Day code = 1) 

Step 3 - Calculate odd days for years, months and days 

Step 4 - Add all and divide by 7 - remainder gives the day

Quick Method for SSC:

If a date and its day is given, find another date:

• Count the number of days between the two dates
• Divide by 7 to get weeks and odd days
• Add odd days to the known day

Example: 

15 August 1947 was Friday. 

What day was 26 January 1950?

Days from 15 Aug 1947 to 26 Jan 1950:

• 15 Aug to 31 Dec 1947 = 138 days
• Full year 1948 (leap) = 366 days
• Full year 1949 = 365 days
• 1 Jan to 26 Jan 1950 = 26 days
• Total = 138 + 366 + 365 + 26 = 895 days
• 895 ÷ 7 = 127 weeks + 6 odd days
• Friday + 6 = Thursday

Answer: Thursday (26 January 1950 was Thursday)

Type 4 - Repeating Day and Date On which date in the same month will the same day repeat?

Simple Rule: Same day repeats every 7 days. 

If 5th is Monday, then 12th, 19th, 26th are also Monday.

How to Solve Calendar Questions:

Step 1 - Identify what is given - a date, a day or a year. 

Step 2 - Count the total days between reference point and target date. 

Step 3 - Divide by 7 and find the remainder (odd days). 

Step 4 - Add odd days to the known day. 

Step 5 - If total exceeds 7, subtract 7 (wrap around the week).

Important Facts to Remember:

• January 1, 2000 was Saturday
• January 1, 2001 was Monday
• A non-leap century year has 5 odd days
• 400 years has exactly 0 odd days (perfect cycle)
• The calendar repeats every 400 years

Quick Tricks:

Trick 1 - For "day after n days" questions: divide n by 7, remainder = extra days to add.

Trick 2 - If today is day X and you add 7 days - you get the same day again.

Trick 3 - Leap year check: if year ends in 00, check if divisible by 400. Otherwise check if divisible by 4.

Trick 4 - Remember odd days for each month - January=3, February=0 (ordinary) or 1 (leap).

Important Tips:

• Memorize the day codes (Sunday=0 to Saturday=6)
• Memorize odd days for each month
• Practice leap year identification daily
• 1 to 2 questions come from this topic in SSC CGL every year
• These questions are solved in under 30 seconds with practice