Guides
The calculators on AskTheDate give you an instant answer; these guides explain the rules behind the answer — how working days are counted, why week numbers disagree, what an earnings estimate actually is. Written by hand, kept short, and linked to the tool that does the arithmetic for you.
Dates & calendars
How Working Days Are Counted
What counts as a business day, how weekends and public holidays differ by country, and why two calculators can give different answers.
ISO Week Numbers Explained
Why January 1st is not always in week 1, how ISO 8601 defines weeks, and where US and European week numbering disagree.
Leap Year Rules, and Why 1900 Was Not One
The divisible-by-4 rule is only a third of the story. The full Gregorian rules, the astronomy behind them, and what happens to February 29 birthdays.
How Age Is Calculated Around the World
Completed years vs counting years, East Asian age reckoning, and the legal fate of people born on February 29.
Counting Days Between Dates: The Off-by-One Trap
Inclusive vs exclusive counting, why "days until" and "days between" can differ by one, and conventions used by banks, lawyers, and calculators.
Time & time zones
Daylight Saving Time and Date Math
Twice a year a day is not 24 hours long. How DST transitions produce 23- and 25-hour days and quietly break naive date calculations.
Time Zones and the IANA Database
What "America/New_York" actually means, why abbreviations like CST are ambiguous, and how the tz database keeps historical time honest.
Markets & earnings
How to Read an Earnings Calendar
What BMO and AMC mean, why report dates shift, how fiscal quarters map to calendar dates, and what to check before trading around a report.
EPS and Earnings Estimates, Explained
What earnings per share measures, where analyst estimates come from, what a "beat" or "miss" means, and why estimates are not promises.