Understand the dates behind the numbers.
Short, worked explanations of the calendar rules that change a result.
How to calculate age in years, months and days
A clear method for counting completed years, calendar months and the remaining days.
Why month-end age calculations go wrong
Understand short months, leap days and the convention used in our calculations.
Count down to your birthday and save the date
Set a reference date, choose a leap-day rule and download a calendar event.
How to compare two birth dates
Find the calendar gap between birthdays and understand why the total days matter.
Inclusive or elapsed days: which count do you need?
Choose between elapsed date intervals and a count that includes both endpoints.
What happens when you add a month to 31 January?
Learn the difference between adding calendar months and adding a fixed number of days.
Traditional Korean age and international age explained
Compare traditional age, year age and completed international years for the same birthday.
What a pet age in human years actually tells you
Read the cat and medium-dog age chart alongside its source and assumptions.
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Count a draft, calculate a percentage, convert a measurement or create a password. Explore the main MultipleTools collection.
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