How do I calculate my age from my date of birth?

Subtract your birth year from the current year. If your birthday has not happened yet this year, subtract one more year from that total. Then count the months and days separately using the same subtract-and-borrow method. This tool does all of that automatically. You just get the finished answer.

Can I calculate my age on a specific date?

Yes. Instead of leaving the calculate-as-of field on today, pick any date, past or future, and the tool works out your age as of that day. Use this for school enrollment cutoffs, immigration age requirements, or figuring out how old you will be on a future date like a wedding or retirement.

How does this handle leap years?

Leap years are built into the calendar math, not added as an afterthought. If someone's birthday is February 29, this tool treats it as February 28 in non-leap years for counting elapsed years, the same convention most legal and administrative systems use, while still calculating the exact day count correctly underneath.

What is chronological age?

Chronological age is the time that has passed since birth, measured in the calendar: years, months, and days. It is different from biological age, which estimates how old a body seems rather than how long a person has actually been alive. When a form or a doctor asks for your age, chronological age is what they mean.

How is Korean age different from international age?

Korean age starts at one, not zero, on the day someone is born, and everyone's age increases together on New Year's Day instead of on individual birthdays. Depending on birth month, that can put Korean age one or two years ahead of the international age most of the world uses. Toggle Also show Korean age to see both numbers at once.

How do I calculate age difference between two people?

Switch to the Age Difference tab, enter both birth dates, and the calculator returns the gap as years, months, and days, plus a flat day count if you need one number instead of three. It works the same way whether the gap is a few months or several decades.

How accurate is this online tool?

It is accurate to the day, using real calendar date math rather than a simplified days-divided-by-365 estimate. Leap years, varying month lengths, and the borrow-a-month logic are all handled correctly. The one thing it cannot account for is a wrong birth date typed in.

How do I calculate age in Excel?

Put the birth date in a cell, then wrap it in Excel's DATEDIF function with "Y", "YM", and "MD" as the unit arguments to pull out years, months, and days separately. The full formula is in the Excel section above. It is the same calendar-based approach this tool uses, just typed out manually.

Yes. Everything runs in your browser using JavaScript. Your birth date never leaves your device. There are no servers processing your information and no account required. You can disconnect from the internet after loading the page and the calculator still works.

Can I use this for my pet?

Yes. Click the Pet Age tab, choose dog or cat, and enter how many years old your pet is. The tool converts to human-equivalent age using the standard veterinary formula, not the old seven dog years equals one human year shortcut.

How Old Is Someone Born on September 29, 2021?

Current age

4 years, 11 months, 13 days

Total days: 1,808
Total weeks: 258
Completed months: 59
Total hours: 43,392
Total minutes: 2,603,520
Total seconds (live): 156,211,200

Next birthday: September 29, 2026 (18 days, turning 5)

Your date of birth

Date of birth

Calculate age as of

Also show Korean age

Results

Total days: 1,808
Total weeks: 258
Total months: 59
Total hours: 43,392
Seconds lived: 0

Elapsed time

Unit	As of September 11, 2026
Years, months, days	4 years, 11 months, 13 days
Total days	1,808
Total weeks (days ÷ 7)	258
Total hours	43,392
Total minutes	2,603,520
Total seconds (at page load)	156,211,200

Age milestones

Age	Date reached	Day of week
1	September 29, 2022	Thursday
5	September 29, 2026	Tuesday
10	September 29, 2031	Monday
13	September 29, 2034	Friday
16	September 29, 2037	Tuesday
18	September 29, 2039	Thursday
21	September 29, 2042	Monday
25	September 29, 2046	Saturday
30	September 29, 2051	Friday
40	September 29, 2061	Thursday
50	September 29, 2071	Tuesday
60	September 29, 2081	Monday
65	September 29, 2086	Sunday
70	September 29, 2091	Saturday
80	September 29, 2101	Thursday
90	September 29, 2111	Tuesday
100	September 29, 2121	Monday

Reference dates

Date	Exact age
Birth date (Wednesday)	0 years, 0 months, 0 days
September 11, 2026	4 years, 11 months, 13 days
September 29, 2026	Turning 5
+1 mo → October 29, 2026	5 years, 1 month
+3 mo → December 29, 2026	5 years, 3 months
+6 mo → March 29, 2027	5 years, 6 months
+9 mo → June 29, 2027	5 years, 9 months
+12 mo → September 29, 2027	6 years

Week milestones from birth

Weeks after birth	Date
1	October 6, 2021
4	October 27, 2021
8	November 24, 2021
13	December 29, 2021
26	March 30, 2022
52	September 28, 2022

Related birth dates

50 related calculations
Birth date	Age today	Page
2021-09-28	4	View
2021-09-30	4	View
2021-09-27	4	View
2021-10-01	4	View
2021-09-26	4	View
2021-10-02	4	View
2021-09-22	4	View
2021-10-06	4	View
2021-09-15	4	View
2021-10-13	4	View
2021-08-30	5	View
2021-10-29	4	View
2021-07-31	5	View
2021-11-28	4	View
2021-07-01	5	View
2021-12-28	4	View
2011-09-29	14	View
2012-09-29	13	View
2013-09-29	12	View
2014-09-29	11	View
2015-09-29	10	View
2016-09-29	9	View
2017-09-29	8	View
2018-09-29	7	View
2019-09-29	6	View
2020-09-29	5	View
2022-09-29	3	View
2023-09-29	2	View
2024-09-29	1	View
2025-09-29	0	View
2026-09-29	—	View
2021-09-01	5	View
2021-09-02	5	View
2021-09-03	5	View
2021-09-04	5	View
2021-09-05	5	View
2021-09-06	5	View
2021-09-07	5	View
2021-09-08	5	View
2021-09-09	5	View
2021-09-10	5	View
2021-09-11	5	View
2021-09-12	4	View
2021-09-13	4	View
2021-09-14	4	View
2021-09-16	4	View
2021-09-17	4	View
2021-09-18	4	View
2021-09-19	4	View
2021-09-20	4	View

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How this is calculated

Exact age counts completed calendar years, months, and days between the birth date and the reference date.
Total days is the count of calendar days elapsed between those dates (including leap days).

Age = Reference date − Birth date

Weeks ≈ total days ÷ 7. Hours = total days × 24. Minutes = total hours × 60 (exact for whole-day spans).