Simple Day Finding problems require determining the day of the week for a given date. You may be given a reference date with its weekday, or you may need to calculate directly using calendar formulas. These problems test your understanding of the 7-day weekly cycle and date arithmetic.

Day After/Before problems ask: 'What day will it be N days after a given day?' or 'What day was it N days ago?' These problems test your understanding of the weekly cycle and modular arithmetic.

Leap Year Check problems ask whether a given year is a leap year. A leap year has 366 days, with February having 29 days. These problems test your knowledge of the Gregorian calendar rules for leap years.

Days in Month problems ask for the number of days in a specific month of a given year. These problems test your knowledge of month lengths and leap year adjustments for February.

Odd/Even Dates problems ask you to count the number of odd-numbered dates (1, 3, 5, etc.) or even-numbered dates (2, 4, 6, etc.) in a given month or year. These problems test your understanding of number patterns in calendar dates.

Calendar Patterns problems ask when a calendar for a given year will repeat. The same calendar repeats when January 1 falls on the same day of week AND the year has the same leap status (leap or non-leap). These problems test your understanding of calendar cycles.

Birthday Weekday problems ask for the day of the week on which a person's birthday falls in a given year, often compared to another year. These problems test your ability to calculate day shifts across years considering leap years.

Weekday Count problems ask how many times a specific weekday (e.g., Monday, Sunday) occurs in a given month or year. These problems test your understanding of how weekdays distribute across months and the pattern of 4 or 5 occurrences.

Date Difference problems ask for the exact number of days between two given dates. These problems test your ability to count days across months and years, accounting for leap years.

Age Calculation problems ask for a person's age on a given date based on their date of birth. These problems test your ability to calculate differences in years, months, and days, accounting for leap years and month lengths.

Century Problems involve identifying which century a year belongs to, or the first and last years of a century. These problems test your understanding of how centuries are numbered and the special rules for century leap years.

Recurring Patterns problems ask when a particular date (e.g., December 25) will fall on the same day of the week as it does in a given year. These problems test your understanding of the 28-year cycle and how dates shift across years.

Week Number Calculation problems ask for the ISO week number of a given date. The ISO week date system defines weeks starting on Monday, with week 1 being the week containing the first Thursday of the year. These problems test understanding of the ISO week numbering system.

Festival and Holiday Date problems ask for the date of a specific festival or holiday in a given year. Some festivals have fixed dates (Christmas, New Year), while others are movable (Easter, Thanksgiving). These problems test knowledge of how festival dates are determined.

Calendar Coding/Decoding problems present days of the week represented by codes (numbers, symbols, or other words). You must decode the code or find the day for a given code. These problems test your ability to apply coding rules to calendar concepts.

Xth Weekday Finder problems ask for the date of the 1st, 2nd, 3rd, 4th, or 5th occurrence of a specific weekday in a given month. These problems test your ability to calculate weekday positions within a month.

Classic Odd Days problems ask for the number of 'odd days' between two dates. An odd day is the remainder when total days are divided by 7. This concept is fundamental to calendar reasoning, especially for finding weekdays without reference dates.

Visual Calendar Reasoning problems present a calendar grid (month view) and ask questions about dates, weekdays, or patterns within that grid. These problems test your ability to interpret visual calendar data and identify patterns.

Total Weekends in a Year problems ask for the number of Saturdays and Sundays (or combined weekend days) in a given year. These problems test your understanding of how 365/366 days distribute across weekdays.

Multi-Calendar and Fiscal Year problems involve different calendar systems (e.g., Gregorian calendar, fiscal year) and require converting dates or determining fiscal year periods. These problems test understanding of non-standard calendar periods.

Same Calendar Year problems ask for a year that has the exact same calendar as a given year (same start day and same leap status). These problems test understanding of calendar cycles and the conditions for calendar repetition.

Day Without Reference problems ask for the day of week of a date without providing a reference date. You must use formulas like Zeller's congruence or the odd days method with a known anchor (e.g., Jan 1, 0001 was Monday) to calculate directly.

Specific Weekday Occurrence problems ask for the date of a particular occurrence of a weekday in a month (e.g., 'the 3rd Tuesday of May' or 'the last Friday of December'). These problems test your ability to navigate calendar positions.

Century End Day problems ask for the day of the week on December 31 of a century year (e.g., Dec 31, 1900, 2000, 2100). These problems test understanding of odd days accumulation over centuries.

Day Between Dates problems give the weekday of one date and ask for the weekday of another date, with a specified number of days between them. These problems test your ability to calculate weekday shifts.

Odd Days Calculation problems ask for the total number of odd days over a period of years, centuries, or between two dates. This is a more advanced version of odd days concept, often used to find the day of week without a reference date.