How the Same Birthday Unlocks Different Things
The same date of birth can meet school, work, driving, voting and pension thresholds at different times. Learn how attained age, cut-off dates and cohorts change the answer.
Calculator Guides
Seven Mistakes People Make Doing Date Maths by Hand
Seven date-maths mistakes produce plausible answers: thirty-day months, month-end overflow, leap days, century rules, daylight saving, endpoint counting and Excel’s 1900 bug.
Days Between Dates: Why Two Correct Answers Exist
From 1 March to 3 March is two days exclusive or three inclusive. Learn which convention applies to deadlines, invoices, contracts and working-day calculations.
Why Multiplying Dog Years by Seven Doesn't Work
The seven-year rule ignores how quickly dogs mature and how strongly size affects lifespan. Compare the rule with veterinary charts and the evidence behind modern estimates.
Gestational Age vs Fetal Age: The Two-Week Gap Nobody Explains
Gestational age starts at the last menstrual period, while fetal age starts at conception. See why the figures differ by about two weeks and what Naegele’s rule assumes.
Where Generations Begin and End, and Why Nobody Agrees
Baby Boomer dates are unusually consistent. Later generations vary by source, so this guide compares Pew ranges, competing boundaries and why the labels keep moving.
How Age Is Counted Around the World
Most countries count age from completed years. This guide compares international age reckoning, traditional Korean age and the rules used on official forms.
Born on 29 February: The Two Conventions Nobody Agrees On
Leap-day birthdays fall on 29 February in leap years. This guide explains the 28 February and 1 March conventions, the 2100 exception and why legal age thresholds can differ.
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