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 21, 1947?

Current age

78 years, 11 months, 21 days

Total days: 28,845
Total weeks: 4,120
Completed months: 947
Total hours: 692,280
Total minutes: 41,536,800
Total seconds (live): 2,492,208,000

Next birthday: September 21, 2026 (10 days, turning 79)

Your date of birth

Date of birth

Calculate age as of

Also show Korean age

Results

Total days: 28,845
Total weeks: 4,120
Total months: 947
Total hours: 692,280
Seconds lived: 0

Elapsed time

Unit	As of September 11, 2026
Years, months, days	78 years, 11 months, 21 days
Total days	28,845
Total weeks (days ÷ 7)	4,120
Total hours	692,280
Total minutes	41,536,800
Total seconds (at page load)	2,492,208,000

Age milestones

Age	Date reached	Day of week
1	September 21, 1948	Tuesday
5	September 21, 1952	Sunday
10	September 21, 1957	Saturday
13	September 21, 1960	Wednesday
16	September 21, 1963	Saturday
18	September 21, 1965	Tuesday
21	September 21, 1968	Saturday
25	September 21, 1972	Thursday
30	September 21, 1977	Wednesday
40	September 21, 1987	Monday
50	September 21, 1997	Sunday
60	September 21, 2007	Friday
65	September 21, 2012	Friday
70	September 21, 2017	Thursday
80	September 21, 2027	Tuesday
90	September 21, 2037	Monday
100	September 21, 2047	Saturday

Reference dates

Date	Exact age
Birth date (Sunday)	0 years, 0 months, 0 days
September 11, 2026	78 years, 11 months, 21 days
September 21, 2026	Turning 79
+1 mo → October 21, 2026	79 years, 1 month
+3 mo → December 21, 2026	79 years, 3 months
+6 mo → March 21, 2027	79 years, 6 months
+9 mo → June 21, 2027	79 years, 9 months
+12 mo → September 21, 2027	80 years

Week milestones from birth

Weeks after birth	Date
1	September 28, 1947
4	October 19, 1947
8	November 16, 1947
13	December 21, 1947
26	March 21, 1948
52	September 19, 1948

Related birth dates

50 related calculations
Birth date	Age today	Page
1947-09-20	78	View
1947-09-22	78	View
1947-09-19	78	View
1947-09-23	78	View
1947-09-18	78	View
1947-09-24	78	View
1947-09-14	78	View
1947-09-28	78	View
1947-09-07	79	View
1947-10-05	78	View
1947-08-22	79	View
1947-10-21	78	View
1947-07-23	79	View
1947-11-20	78	View
1947-06-23	79	View
1947-12-20	78	View
1937-09-21	88	View
1938-09-21	87	View
1939-09-21	86	View
1940-09-21	85	View
1941-09-21	84	View
1942-09-21	83	View
1943-09-21	82	View
1944-09-21	81	View
1945-09-21	80	View
1946-09-21	79	View
1948-09-21	77	View
1949-09-21	76	View
1950-09-21	75	View
1951-09-21	74	View
1952-09-21	73	View
1953-09-21	72	View
1954-09-21	71	View
1955-09-21	70	View
1956-09-21	69	View
1957-09-21	68	View
1947-09-01	79	View
1947-09-02	79	View
1947-09-03	79	View
1947-09-04	79	View
1947-09-05	79	View
1947-09-06	79	View
1947-09-08	79	View
1947-09-09	79	View
1947-09-10	79	View
1947-09-11	79	View
1947-09-12	78	View
1947-09-13	78	View
1947-09-15	78	View
1947-09-16	78	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).