Date Calculator
Calculate day of year, week number, days between dates, and project future/past dates. Useful for date-based puzzles.
Day of Year
338
Week Number
49
Day of Week
Thursday
Day #
4
(0=Sun, 6=Sat)
Date Details
Days Between Dates
Add/Subtract Days
Puzzle Tips
- • Day of year can be coordinates (1-365/366)
- • Week numbers might be clues (1-52)
- • Historical dates often appear in puzzles
- • Julian dates are useful for astronomical caches
- • Days since an event might be significant
About Date Calculations
This tool provides various date calculations commonly needed for geocaching puzzles and general reference. Convert dates to day-of-year, calculate days between dates, and more.
Date Values Explained
Day of Year
The number from 1-365 (or 366 in leap years) indicating which day of the year it is. January 1 = Day 1, December 31 = Day 365/366.
Week Number (ISO)
The week number according to ISO 8601 standard. Weeks start on Monday, and Week 1 is the week containing the first Thursday of the year.
Julian Date
A continuous count of days since January 1, 4713 BC. Used in astronomy and some scientific applications. Allows easy calculation of time intervals.
Date Calculations in Geocaching
Dates are commonly used in puzzles:
- Historical events: "Day Apollo 11 landed" = Day 201 (July 20)
- Personal dates: Cache owner's birthday, founding dates
- Days between: "Days since cache was published"
- Projected dates: "100 days after event X"
- Day of week: Might indicate a digit (Sun=0 or 1)
Common Date Puzzles
- Coordinates from dates: Day of year as coordinate digits
- Checksum verification: Date-based calculations verify answers
- Julian date puzzles: Astronomy-themed caches
- Anniversary puzzles: Find the date, calculate values