Dates look simple until you add leap years, months of different lengths and time zones. These tools do the counting for you and show the arithmetic, so you can check any result by hand.
Start with the age calculator for an exact age in years, months and days, use the date and days-between calculators for deadlines and planning, or count down to a holiday. The birthday and retirement age tools build on the same date math, and every page includes a formula and a worked example.
Age Calculator by Date of Birth
Exact age, total days lived, next birthday
🎉Birthday Calculator
Day you were born, zodiac, generation
📅Days Between Dates Calculator
Count days, weeks and weekdays
🗓️Date Calculator
Add or subtract days from a date
⏳Days Until Calculator
Countdown to holidays and dates
🎄Days Until Christmas
Days, sleeps and weeks to go
🌴Retirement Age Calculator
Full retirement age and date (US)
🌍Time Zone Converter
Convert times between cities
📖 GuidesAll guides
When Does Daylight Saving Time End? Dates for 2026 to 2030
The dates daylight saving time ends and starts in the US and Europe from 2026 to 2030, how the rules work, who skips it, and what changes for scheduling.
When Is Thanksgiving? Dates for 2026 to 2032 (US and Canada)
US Thanksgiving is the fourth Thursday of November. See the dates for 2026 to 2032, plus Black Friday and Canadian Thanksgiving, and how to count the days left.
How Many Days Until Halloween? Date, Weekday and Countdown
Halloween is always October 31. See which weekday it falls on from 2026 to 2031, where the holiday comes from, and how to count the days left.
How to Calculate Age From a Date of Birth (Step by Step)
Learn how to calculate exact age in years, months and days from a date of birth, with worked examples, leap year tips and the mistakes to avoid.
Leap Years Explained: Rules, Examples and Leap Day Birthdays
Why we have leap years, the exact rule for which years count, how leap day birthdays work and how a leap year changes date calculations.
Full Retirement Age Explained (US Social Security)
What full retirement age is, how it depends on your birth year, what claiming at 62 or 70 does to your benefit, and how it differs from Medicare eligibility.
How Old Am I? Age Chart by Birth Year
Find your age from your birth year with a simple chart that updates each year, plus how to get your exact age in years, months and days.
Chronological Age vs Biological Age: What's the Difference?
Chronological age counts the years since birth, while biological age tries to estimate how your body is aging. Learn how each works and what to trust.
Time Zones Explained: UTC, Offsets and Scheduling Mistakes
How time zones and UTC offsets work, why abbreviations like CST are ambiguous, how daylight saving changes offsets, and how to schedule across zones.