Date Math: Days Between Dates, Age & Weekdays
Working with dates by hand is error-prone — months have different lengths and leap years shift things. Here’s how the common date calculations work.
Counting days between dates
The reliable way is to convert both dates to a day count and subtract. That automatically handles month lengths and leap years. The Date Difference Calculator does this and also shows the gap in weeks, months and years.
Working out an exact age
Age isn’t just “this year minus birth year” — it depends on whether your birthday has passed yet this year. The Age Calculator accounts for that and gives your age in years, months and days.
Which weekday is a date?
Every date falls on a fixed weekday, and you can find it without a calendar. The Day of the Week Calculator tells you instantly — handy for planning events or checking historical dates.
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Last updated: July 6, 2026