Calendar months have different lengths, so an exact age is found by counting whole years, then whole months, then the leftover days – the same way people normally state their age. Totals in weeks, days or seconds are simple multiples of the number of days. People born on 29 February celebrate on 28 February in non-leap years here.
How to use the Age Calculator
- Date of birth
- Age on this date
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter your date of birth and the date you want your age on (today by default).
Tips
- Check whether the end date should be included – event durations usually include it, elapsed time does not.
- Months have 28–31 days, so “one month” is counted by calendar date, not as 30 days.
- Use 24-hour time or set AM/PM carefully when entering clock times.
- Time zones and daylight-saving changes are not applied unless the calculator says so.
Common mistakes to avoid
- Counting a 30-day month when a calendar month is meant (or the reverse).
- Forgetting leap years when counting days across February.
- Mixing decimal hours (7.5 h) with clock time (7:30).
Inputs explained
| Field | What to enter |
|---|---|
| Date of birth | A date |
| Age on this date | A date |
What each result means
- Age = floor([Total full months]÷12)
- and months = [Total full months] – 12×floor([Total full months]÷12)
- and days = [Age on this date] – addmonths([Date of birth], [Total full months])
- Age in months = [Total full months]
- Age in weeks = floor(([Age on this date] – [Date of birth])÷7)
- Age in days = [Age on this date] – [Date of birth]
- Age in hours = ([Age on this date] – [Date of birth])×24
- Age in minutes = ([Age on this date] – [Date of birth])×1440
- Age in seconds = ([Age on this date] – [Date of birth])×86400
- You were born on a = weekday([Date of birth])
- Days until next birthday = addmonths([Date of birth], (floor([Total full months]÷12) + 1)×12) – [Age on this date]
Formula
Age = whole years, then whole months, then remaining days from your date of birth to the chosen dateAge in days = date − date of birth; hours = days × 24; minutes = hours × 60Worked example
Inputs — Date of birth: 1995-06-15; Age on this date: 2026-10-25.
Results — Age = 31 years; and months = 4; and days = 10; Age in months = 376; Age in weeks = 1,636; Age in days = 11,455; Age in hours = 274,920; Age in minutes = 16,495,200; Age in seconds = 989,712,000; You were born on a = Thursday; Days until next birthday = 233; Star sign = Gemini ♊; Chinese zodiac = Pig 🐖.
Frequently asked questions
How do I calculate my exact age?
Count the full years since your birthday, then the full months since your last birthday, then the days since the last monthly anniversary.
How many days old am I?
Subtract your date of birth from today's date – the result above does it for you.
How is age counted for 29 February birthdays?
Legally most countries treat 28 February (or 1 March) as the birthday in non-leap years; this calculator uses 28 February.
What formula does the Age Calculator use?
Age = whole years, then whole months, then remaining days from your date of birth to the chosen date.