Day of the week for any date — Mental Maths Mastery
Every 7 days the weekday comes back, so only the left-over days matter. Each month has a code (the days before it, minus whole weeks). Start from the weekday of 1 January, add the month code and the date, and throw away whole weeks.
Month code + date — “only the days left over after whole weeks move the weekday”
Month codes for 2026 and 2027: Jan 0, Feb 3, Mar 3, Apr 6, May 1, Jun 4, Jul 6, Aug 2, Sep 5, Oct 0, Nov 3, Dec 5. In a leap year like 2028, add 1 from March on.
1 January 2026 is a Thursday and 1 January 2027 is a Friday. Add the month code and (date − 1).
Take away 7s until less than 7 is left, and move that many days on from 1 January.
Use it for: Planning birthdays, holidays and exam dates, and calendar puzzles in Olympiads.
Worked example: 1 January 2027 is a Friday. What day is 26 March 2027? Friday
March code: 3. The date is 25 days after the 1st = 3 weeks and 4 days.
3 + 4 = 7, a whole week, so move 0 days.
Check: 1 January to 26 March is 31 + 28 + 25 = 84 days = exactly 12 weeks, so it is a Friday too ✓
Work it out in your head or on paper, then tap your answer — or type it and press Check. Stuck? Press “Show me how”.
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🏁 Lesson 28 test
20 questions. Check each answer, then go to the next one. Get 16 or more right to pass.
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