Online Age Calculator – Calculate Exact Age

How Old Am I? — How This Calculator Works

Our age calculator computes the precise difference between your date of birth and a target date (defaulting to today). It accounts for varying month lengths (28, 29, 30, or 31 days) and correctly handles leap years, giving you accurate results in years, months, and days. Beyond basic age, it also shows your total age in days, weeks, and months — and tells you exactly how many days remain until your next birthday.

The calculation uses the international (Western) age system where you are age 0 at birth and your age increments on each birthday. If you enter a target date in the future, the calculator shows what your age will be on that date — useful for eligibility checks, milestone planning, and event countdowns.

How to Calculate Age by Hand

There are two reliable methods for calculating age manually. Both give accurate results; the first is more intuitive for everyday use, while the second is useful for spreadsheet-based calculations.

Method 1: Long Subtraction (Borrowing)

This method works like subtraction with carrying, using the date format YYYY MM DD. Place the more recent date on top and the older date on the bottom, then subtract right to left:

1. Subtract days. If the result is negative, borrow 1 from the months column. The number of days you borrow equals the number of days in the previous month.
2. Subtract months. If the result is negative, borrow 1 from the years column (add 12 months).
3. Subtract years.

Worked Example: Calculate the age of someone born November 15, 1995 as of April 4, 2026.

• Set up: 2026 04 04 (top) minus 1995 11 15 (bottom)
• Days: 4 − 15 = negative → borrow 1 month. March has 31 days, so: 4 + 31 = 35. Then 35 − 15 = 20 days
• Months: 4 − 1 (borrowed) = 3. Then 3 − 11 = negative → borrow 1 year (add 12): 3 + 12 = 15. Then 15 − 11 = 4 months
• Years: 2026 − 1 (borrowed) = 2025. Then 2025 − 1995 = 30 years

Method 2: Total Days Division

Count the total number of days between the two dates, then divide by 365.2425 (the average length of a Gregorian calendar year, accounting for leap years):

• Total days between Nov 15, 1995 and Apr 4, 2026 = 11,098 days
• 11,098 ÷ 365.2425 = 30.38 years ≈ 30 years and ~4.6 months

This method gives an approximate result. For exact years/months/days, the long subtraction method or our calculator is more precise.

Age in Different Units — Conversion Chart

How old are you in days? In weeks? In hours? This reference chart converts common ages into different time units. Approximate values assume 365.25 days per year (accounting for leap years).

Age (Years)	Days	Weeks	Months	Hours
1	365	52	12	8,766
5	1,826	261	60	43,830
10	3,652	522	120	87,660
16	5,844	835	192	140,256
18	6,574	939	216	157,766
21	7,670	1,096	252	184,082
25	9,131	1,304	300	219,145
30	10,957	1,565	360	262,974
40	14,610	2,087	480	350,640
50	18,262	2,609	600	438,300
62	22,645	3,235	744	543,490
65	23,741	3,392	780	569,790
67	24,472	3,496	804	587,322
80	29,220	4,174	960	701,280

Leap years add 1 day for every 4 years. A person who turns 40 has experienced approximately 10 leap days.

Age Systems Around the World

Age is not counted the same way in every culture. Our calculator uses the international (Western) system, which is the legal standard in the United States and most countries. Here's how systems differ:

International (Western) Age System

You are age 0 at birth, and your age increases by 1 on each birthday. A person born on March 15, 2000 turns 26 on March 15, 2026. This is the system used in the United States, all of Europe, and most of the modern world. It is the basis for all legal age calculations — voting eligibility, drinking age, Social Security benefits, etc.

Korean Age System

In the traditional Korean system, you are age 1 at birth, and everyone's age increments by 1 on January 1 (not on their birthday). A baby born on December 31 would be "1" at birth and turn "2" the very next day on January 1 — making them "2 years old" when only 1 day old.

Important update: South Korea officially switched to the international age system in June 2023 for all legal and administrative purposes. Korean age is still used informally in social contexts.

Chinese Lunar Age System

Similar to Korean age, the traditional Chinese system counts you as 1 at birth, with age incrementing on Lunar New Year (late January or February). This system is used in some traditional Chinese contexts and is sometimes referenced in Chinese astrology.

Comparison Example

System	Born Dec 20, 2000	Age on Jan 5, 2026
International (Western)	Age 0 at birth	25 years old
Korean (traditional)	Age 1 at birth	27 years old
Chinese Lunar	Age 1 at birth	27 years old (if after Lunar New Year)

What If You Were Born on a Leap Day? (February 29)

Approximately 4.1 million Americans have a February 29 birthday — roughly a 1-in-1,461 chance. Leap Day babies (sometimes called "leaplings") face a unique question: what is your birthday in non-leap years?

• Most U.S. states legally recognize March 1 as the birthday in non-leap years for age-related milestones (driver's license, voting, drinking age).
• Some states and agencies use February 28 instead.
• The Social Security Administration uses March 1 for benefit calculations in non-leap years.
• International practice varies — in New Zealand, the legal birthday in non-leap years is February 28; in Hong Kong and Taiwan, it is March 1.

Our calculator handles leap year birthdays correctly — it counts your exact chronological age regardless of whether the current year is a leap year.

How to Calculate Age in Excel or Google Sheets

You can calculate exact age in Microsoft Excel or Google Sheets using the DATEDIF function. Although this function is undocumented in Excel's official help, it works reliably in all versions.

Step-by-Step Formulas

Assume your date of birth is in cell A1 (e.g., 11/15/1995):

What to Calculate	Formula	Result Example
Years	=DATEDIF(A1, TODAY(), "Y")	30
Remaining Months	=DATEDIF(A1, TODAY(), "YM")	4
Remaining Days	=DATEDIF(A1, TODAY(), "MD")	20

Combine into One Cell

To display the full age as a single readable string:

=DATEDIF(A1,TODAY(),"Y") & " years, " & DATEDIF(A1,TODAY(),"YM") & " months, " & DATEDIF(A1,TODAY(),"MD") & " days"

This outputs: 30 years, 4 months, 20 days. The same formulas work identically in Google Sheets.

How Old Is My Baby?

Pediatricians in the United States use age-specific milestones that require precise age tracking in different units:

• First 6 months: Baby age is measured in weeks (e.g., "my baby is 12 weeks old")
• 6 months to 2 years: Age is measured in months (e.g., "she is 14 months old")
• After 2 years: Age is measured in years and months (e.g., "he is 3 years and 2 months")

Our calculator automatically shows total weeks in the results, which is exactly what you need for well-baby checkup scheduling. The CDC recommended immunization schedule uses weeks and months for all pediatric appointments.

Standard Pediatric Checkup Schedule

Checkup	Baby Age	Key Milestone
Newborn	3–5 days	Weight check, jaundice screening
1 month	4 weeks	Feeding assessment, Hep B vaccine
2 months	8 weeks	DTaP, IPV, Hib, PCV13, Rotavirus vaccines
4 months	16 weeks	Second round of infant vaccines
6 months	26 weeks	Flu vaccine (first eligible age)
9 months	39 weeks	Developmental screening
12 months	52 weeks	MMR, Varicella, Hep A vaccines

Days Per Month Reference

Month	Days	Note
January	31
February	28 / 29	29 in leap years
March	31
April	30
May	31
June	30
July	31
August	31
September	30
October	31
November	30
December	31

Mnemonic: "Thirty days hath September, April, June, and November. All the rest have thirty-one, except February alone."

Leap year rule: A year is a leap year if divisible by 4, except for century years — unless they're also divisible by 400. So 2000 was a leap year (divisible by 400), but 1900 was not (divisible by 100 but not 400). The next century leap year is 2400.

U.S. Legal Age Milestones

Many rights and responsibilities in the United States are tied to specific age thresholds. Use this calculator to check eligibility:

Milestone	Minimum Age	Notes
Driver's Learner Permit	14–16	Varies by state (14 in South Dakota, 15 in many states, 16 in some)
Driver's License	16–17	16 in most states with restrictions; full license at 18 in many
Voting	18	26th Amendment (1971); must register before Election Day
Military Enlistment	17–18	17 with parental consent; 18 without
Legal Drinking Age	21	National Minimum Drinking Age Act (1984) — all 50 states
Car Rental (most companies)	25	Can rent at 21 with surcharge; 25 with no surcharge at most agencies
Running for U.S. House	25	U.S. Constitution, Article I, Section 2
Running for U.S. Senate	30	U.S. Constitution, Article I, Section 3
Running for President	35	U.S. Constitution, Article II, Section 1
Social Security (early)	62	Reduced benefits; benefit reduced ~6.7%/yr before full retirement age
Medicare Eligibility	65	Parts A & B; enrollment window is 7 months around 65th birthday
Social Security (full)	66–67	Full retirement age depends on birth year (1960+: age 67)

How Many Days Until My Birthday?

Our calculator automatically shows the number of days remaining until your next birthday at the top of the results. This countdown is recalculated each time you use the tool.

For countdowns to other events — vacations, deadlines, holidays, or milestones — use our Days Until Calculator or Birthday Countdown Timer.