Enter the birth date
Use the complete day, month and four-digit year. The calculator treats it as a calendar date, not a time of day, and never puts it in the page URL.
Exact calendar age
Age Calculator
Enter a date of birth to see an age today, on a past date, or on a future date. You can also enter an age and get the possible birth-date range.
Age calculator
Calculate an age or possible birth date
Use calendar dates only. Nothing you enter is sent or saved.AnswerExact age26y 8m 12d
The exact age is 26 years, 8 months and 12 days.
- Whole months
- 320
- Total weeks
- 1,393 weeks, 1 days
- Total days
- 9,752
Method
checking date - birth date = age- Count full birthdays for the years.
- Count full calendar months after the last birthday.
- Show the days left over and the total days separately.
How it works
How to use the age calculator
Enter the dates, choose any needed option, and read the result with the method shown.
Choose the reference date
Leave today selected for current age, or enter a past or future date to answer how old someone was or will be on that date.
Read the result
The main answer shows years, months and days. Extra details show whole months, weeks and total days.
Completed years
Start with birthdays that have already happened
Subtract the birth year from the year you are checking. Then ask one simple question: has the birthday happened yet in that year? If not, subtract one.
That birthday check is the part people often miss. Someone born on 20 December 1990 is still 35 on 11 September 2026, even though 2026 minus 1990 equals 36.
full years = checking year - birth year2026 - 1990 = 36, then subtract 1 because the birthday is still ahead.
Remaining months and days
Then count from the last birthday
Once you have the years, start at the last birthday and count full calendar months. Stop before you pass the date you are checking. The days left over are the remaining days.
This keeps February, leap years and short months honest. It avoids pretending every month has 30 days or every year has 365 days.
exact age = full years + full months + remaining days35 years + 8 months + 22 days = 35 years, 8 months, 22 days.
Reverse mode
A whole age gives a possible date range
If someone is 30 on 11 September 2026, their 30th birthday happened sometime from 12 September 2025 to 11 September 2026. That means their birth date could be 12 September 1995 through 11 September 1996.
The calculator shows the whole possible range. It does not guess one exact birthday, because a whole age is not enough information.
possible birth dates = reference date - age through reference date - (age + 1 year) + 1 dayAge 30 on 11 September 2026 = 12 September 1995 through 11 September 1996.
Keep this handy
Which age result answers your question?
Use the reference date and output that match the information you actually need.
| Question | Input | Result |
|---|---|---|
| How old am I today? | Birth date + today | Completed years, months and days |
| How old was I on a date? | Birth date + past reference date | Age on that past date |
| How old will I be? | Birth date + future reference date | Age on that future date |
| When could someone aged 30 have been born? | Whole age + reference date | Possible birth-date range |
| How many days old? | Birth date + reference date | Total calendar days |
Follow the calculation
Worked age calculator examples
Each example uses the same calendar rules as the calculator.
1
Birthday today
11 September 2000 to 11 September 2026
26 years, 0 months, 0 days- Count 26 birthdays.
- There are no extra months after the birthday.
- There are no extra days either.
When the checking date is the birthday, the new age has been reached.
2
Birthday still ahead
20 December 1990 to 11 September 2026
35 years, 8 months, 22 days- The December birthday has not happened in 2026, so count 35 years.
- Move from 20 December 2025 through eight complete months to 20 August 2026.
- Count 22 remaining days to 11 September.
Simple year subtraction would be one year too high.
3
Reverse a known age
Age 30 on 11 September 2026
Born from 12 September 1995 through 11 September 1996- The latest possible birthday is 11 September 1996.
- The earliest possible birthday is 12 September 1995.
- Keep both dates because the exact birthday is unknown.
This is a date range, not a guessed birthday.
Calendar details
Edge cases the calculator handles
These are the small details where quick shortcuts often get the wrong date.
29 February births
In a non-leap year, 29 February is missing. Choose 28 February or 1 March instead of assuming one answer works everywhere.
Month-end dates
Some months are shorter than others. If a target month has no 29th, 30th or 31st, the calculator uses the last real date in that month.
Future dates
You can check a future age. A date before the birth date is not allowed because the person had not been born yet.
Dates without times
This uses dates only. It does not claim exact hours since birth because it does not ask for birth time or time zone.
Avoid mistakes
Common age calculator mistakes
A few quick checks make the answer easier to trust.
Subtracting years and stopping
Always check whether the birthday has happened. Before the birthday, year subtraction is one too high.
Treating every year as 365 days
Leap days add up. Multiplying age by 365 will not give the exact total days.
Calling a range an exact birthday
A whole age usually covers many possible birth dates. Show the range, not one made-up date.
Mixing dates and clock times
Date-only inputs can answer calendar-day questions. Exact seconds or hours need a birth time and time zone.
Choose the right page
More age and birthday calculators
Use the page that matches the question you actually have.
Prefer the method in prose? Read how to calculate age. See the manual calendar method, worked examples and common mistakes.
Related guides
Read the calendar method behind the result
These guides explain the rules that most often change an age, birthday or day-count answer.
References
Sources and calendar conventions
These references support the calendar facts and definitions used on this page. Calculator-specific choices are disclosed separately.
- U.S. Naval Observatory: Introduction to CalendarsClear background on calendar months and leap years.
- U.S. Naval Observatory: Leap YearsOfficial explanation of the leap-year rule, including century years.
FAQ
Age Calculator questions
Short answers to the questions that usually come up after using the calculator.
How do I calculate my exact age?
Count full birthdays first. Then count full calendar months from the last birthday. Then count the days left over.
Can I calculate my age on a past or future date?
Yes. Replace today with the relevant reference date. The date must be on or after the date of birth.
Why is my age not the current year minus my birth year?
That subtraction is correct only after your birthday has occurred in the current year. Before your birthday, subtract one more year.
Can a whole age reveal an exact date of birth?
No. It gives a possible range of birth dates. You need more information to know the exact date.
How are leap-day birthdays handled?
For non-leap years, choose either 28 February or 1 March. The calculator exposes the policy because official and personal conventions can differ.
Does this calculate biological or corrected age?
No. It calculates chronological calendar age only and does not assess health, development, prematurity or eligibility.