Calendar Reasoning Cheat Sheet
31 Oct 2026
Quick answer
A quick revision cheat sheet on calendar problems for SSC, Banking, Railway and state exams. It explains the odd-days method, the leap-year rule, the odd days in ordinary and leap years and in 100, 200, 300 and 400 years, and how to find the day of the week for any date, with a worked example.
Calendar Reasoning Cheat Sheet
Quick Revision
Calendar questions ask for the day of the week on some date. The tool for this is the odd day — the number of days left over after counting complete weeks.
1. Odd Days
Odd days = days remaining after taking out complete weeks.
Odd days = (total days) mod 7| Period | Odd days |
|---|---|
| Ordinary year (365 days) | 1 |
| Leap year (366 days) | 2 |
2. The Leap Year Rule
- A year divisible by 4 is a leap year…
- …except a century year, which must be divisible by 400.
So 2000 and 2400 are leap years; 1900 and 2100 are not.
3. Odd Days in Centuries
| Years | Odd days |
|---|---|
| 100 | 5 |
| 200 | 3 |
| 300 | 1 |
| 400 | 0 |
The pattern repeats every 400 years. (For example, 100 years hold 76 ordinary + 24 leap years → 76 + 48 = 124 days → 124 mod 7 = 5 odd days.)
4. Day from Odd Days
Count total odd days from a known reference, then map:
| Odd days | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|---|
| Day (from Sunday) | Sun | Mon | Tue | Wed | Thu | Fri | Sat |
5. Worked Example
The same date one year later moves on by the year's odd days — by 1 day after an ordinary year, or 2 days after a leap year.
If 1 January 2023 was a Sunday, then 1 January 2024 is one day later (2023 is an ordinary year):
Sunday + 1 odd day = Monday6. Exam Quick Tips
- Ordinary year = 1 odd day, leap year = 2 odd days.
- A century year is a leap year only if divisible by 400.
- Centuries: 100 → 5, 200 → 3, 300 → 1, 400 → 0 odd days.
- Convert total odd days with mod 7, then read the day off the table.
Keep revising with the rest of the Reasoning section:
How this was made: Drafted with AI assistance; spot-checked by the editor on 31 October 2026.