Calendar Reasoning
Calendar Reasoning
Calendar reasoning involves finding the day of the week for any given date using the odd days method. It requires knowledge of leap year rules and systematic counting of remainder days.
Key Idea
Count the total number of odd days (remainder when total days are divided by 7) from a reference point. 0 = Sunday, 1 = Monday, ... 6 = Saturday.
Core Rules
Odd Days in a Year
Ordinary year = 1 odd day (365 = 52 weeks + 1 day). Leap year = 2 odd days (366 = 52 weeks + 2 days).
When calculating the day shift across one or more years.
Leap Year Rule
Divisible by 4 → leap. Century years: divisible by 400 → leap, else not. So 1900 is NOT a leap year, but 2000 IS.
When determining if a year has 365 or 366 days.
Century Odd Days
100 years = 5 odd days. 200 years = 3 odd days. 300 years = 1 odd day. 400 years = 0 odd days.
Shortcut for quickly computing odd days across centuries.
Month Odd Days
Jan=3, Feb=0(or 1 in leap), Mar=3, Apr=2, May=3, Jun=2, Jul=3, Aug=3, Sep=2, Oct=3, Nov=2, Dec=3
When computing the day for a specific date within a year.
Day Code
0=Sun, 1=Mon, 2=Tue, 3=Wed, 4=Thu, 5=Fri, 6=Sat
Final step — convert total odd days (mod 7) to the day name.
Relevant Exams
Calendar questions appear in 1-2 questions in SSC CGL and RRB NTPC. Once the odd days table is memorized, these are quick 30-second solves.