Calendar Reasoning
Calendar Reasoning
SSC CGL and RRB NTPC include 1-2 calendar questions that ask you to find the day of the week for a given date. You solve them by counting odd days — the remainder when total days divide by 7 — from a known reference point. Memorizing the leap year rules and century odd-day shortcuts turns these into 30-second solves. The odd days method works for any date in history or the future.
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).
Apply this to calculate how many days the weekday shifts when you move across one or more full 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.
Check this rule first to decide whether a year contributes 1 or 2 odd days to your count.
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.