Age Calculator

• Related: Quarter & Half Birthday Calculator

When people ask, “How old am I today?” the answer they usually expect is the number of birthdays they’ve celebrated; the number adds up every year. But if you want to know more than your completed years, our age calculator has you covered. You can useit to find the years, months, and days between two dates using your birthdate, and even calculate the length of time between the two dates.

Enter the date of birth and “Calculate Age On” to find age at any given date (i.e., today, a date in the past, or in the future) to see your age in years, months, and days. Beyond that, the calculator will also give you the total number of days you have lived, total weeks, and even how many hours, minutes, or seconds have passed since you (or a person) was born.

What is My Age or How Old Am I?

On the surface, the age is the number of birthdays you’ve celebrated, or in general, the age for anything is the total time to date since it came into the world. If you were born on July 10, 2000, then the result on July 10, 2025, is 25 years old. Simple enough. But what about July 2, 2025? Are you 24, almost 25, or 24 years and 11 months?

That’s where a chronological age calculator comes into play beyond casual count. Rather than subtracting the birth year from the current year, it traces the exact passage of time. So on July 2, 2025, you’ll get the answer as 24 years, 11 months, and 22 days. With age presented in different formats, the calculator provides a clear whole picture.

How Old is My Child?

For parents, age is never measured in whole years, especially in the first few years of a child’s life. Doctors ask for a baby’s age in weeks or months, and parents also think in these terms. A 9-week-old newborn is easy to mention as “over 2 months” rather than “0 years old”. This calculator makes that process automatic.

Enter your child’s date of birth, today’s date, and click “Calculate.” The calculator will tell their exact age in weeks, days, and months when possible. It’s especially useful to track developmental milestones, vaccination schedules, or when someone asks, “How old is your baby now?” Instead of mentally converting weeks to months or guessing, you can give the exact answer right away.

The same applies to slightly older children. Parents normally want to know how old their child will be when school starts, when they become eligible for a particular activity, or on a certain future date. Enter that specific day in the “Calculate Age On” field (the default date is set to today), and the tool will provide all age calculation details for it. It will tell you not only if your child will be “5 years old” next September but also how many years, months, and days they’ll have been alive by then.

• Related: Dog Age Calculator

How Age is Calculated

In technical terms, age is a time gap between two calendar dates: your birth date and the date you’re about to measure against. But due to the uneven calendar, such as months with different lengths, leap years, and partial months, it becomes hard to manually subtract years. But you don’t have to worry about it because our age finder is built to handle these complications automatically.

Calendar-based calculation (years, months, and days)

The calculator first finds the difference in years, then checks whether the birth month and day have already happened in the given calculation year. If they haven’t, it subtracts a year and adds the leftover months back into the count. Finally, it calculates the number of days by checking how many days were in the months being compared.

For example, someone born on February 28, 2000, would be exactly 21 years old on February 28, 2021. But if you want to know how old on March 31, 2021, it becomes a little complex. Do we say they are “21 years and 1 month old,” or “21 years, 1 month, 3 days”? The tool reports it as 21 years, 1 month, and 3 days old. This method is accurate and respects the irregular structure of the calendar, including uneven months, leap years, and all.

Total time calculation (days, weeks, hours, minutes, seconds)

In most cases, you don’t ask for calendar years but want to know the raw time length. To figure it out, the calculator uses the exact timestamps of both dates and measures the difference in milliseconds. From there, it converts the timespan into days, then into larger or smaller units like weeks, hours, minutes, or seconds.

For situations where you care less about birthdays and more about raw time lived, the tool works like a stopwatch. It measures the exact span in milliseconds, then converts that into days, and from there into weeks, hours, minutes, or even seconds. This way, you get a true picture of total time passed, not only calendar years.

Running Age vs. Completed Age

Completed age is the age you have fully lived since your birth. For example, if you were born on July 10, 2010, and today is September 2, 2025, you have completed 15 years. That’s the most common way people tell age in daily life when someone asks, “How old are you?” The direct answer is “I am 15 years old.”

Running age, on the other hand, considers the year of life you are currently living in. Take the same example, after your 15th birthday on July 10, 2025, you are in the 16th year. So your running age will be 16, even though you’ve only completed 15 full years. In daily life conversation, we don’t usually say this, but it often appears in forms or eligibility rules that say “must not have completed 16 years as of…” or “under 16 years.”

The calculator shows your completed age by default. In some cultures, like in parts of India and Korea, people use running age instead of completed age. There is no wrong answer; it depends on how you prefer to say it. Many places mention what age to enter when the birthdate is required.

Cultural Differences in Age Systems

Although the whole world uses the same Western system of counting age, where a person starts from 0 years old at birth and grows one year older with each birthday, not all cultures follow the same. Age, after all, is a social concept as much as it’s a mathematical one, and history shows that different societies have developed their own ways to measure it.

For example, in traditional East Asian systems, including the Korean and Chinese, a newborn is considered already one year old at birth, and instead of waiting for their birthday anniversary, every baby grows one year old on the Lunar New Year. This means that a baby born a few days before the new year turns two years old within days, even though he/she only arrived in the world some days ago.

Even in the Western system, there can be differences. Some cultures describe a person’s age not as the number of years completed, but as the year of life they are currently living. Someone who has lived for 20 full years and is partway through their 21st year is told as “in their twenty-first year” instead of “20 years old.”

It’s tough to calculate ages due to these variations in cultures. So, our age calculator uses the most widely accepted global standard: start at zero and add a year for every birthday.

Manual Age Calculation

1. Subtract the birth year from the current year to get the base age in years.
2. If the current month is earlier in the calendar than the birth month, subtract one year from total and adjust the month.
3. If the current day is earlier than the birth day, borrow days from the previous month. The number of days borrowed is based on how many days the month has (28, 29, 30, or 31).
4. Combine results. Once months and days are adjusted, the final age will be completed years, alongside months and days since the last birthday.

Example Age Calculation

Suppose someone was born on August 25, 1998, and you want to know their age on January 12, 2024.

Set up the dates like subtraction:

2024 1 12 − 1998 8 25 =

Subtract days, 25 from 12. Since 12 is smaller than 25, borrow 1 month from January (month 1). That shifts you back into December 2023, which has 31 days. Add the days to 12:

12 + 31 = 43
43 – 25 = 18 days

Now it looks like this:

2023 12 43 − 1998 8 25 = 18 days

Next, subtract months, 8 from 12:

12 – 8 = 4 months
2023 12 43 − 1998 8 25 = 4 months 18 days

Finally, subtract the years, 1998 from 2023:

2023 – 1998 = 25 years

So the age is:

2023 12 43 − 1998 8 25 = 25 years 4 months 18 days

On January 12, 2024, the person is 25 years, 4 months, and 18 days old. In total units, that’s about 9,272 days, or 1,324 weeks and 4 days, or roughly 25.38 years when expressed in decimals.

How Old Will I Be in a Given Year?

How old will I be in 2030, 2040, 2045, or 2050? Calculating the age at a specific time in the future works the same way as finding the past years. You can select any future date in the “Age at the date of” field and click Calculate to get future age results. For the manual process, take the year you’re curious about and subtract your birth year.

For example, if you were born in 1999, you’ll be:

• 31 years old in 2030 (2030 – 1999 = 31)
• 46 years old in 2045 (2045 – 1999 = 46)
• 50 years old in 2049 (2049 – 1999 = 50)

If you were born in 2000, then:

• 30 years old in 2030
• 45 years old in 2045
• 50 years old in 2050

Now, if your birthday hasn’t taken place yet in that year, subtract one. So if you were born in October 1998 and want to know how old in June 2035, you will be 36 years old, not 37 yet. If you ever need a fast mind estimate, the only thing to remember is: future year – birth year = your age that year.

How Old Will I Be on Given Date?

Want to satisfy simple curiosity like, “How old will I be on New Year’s Eve in 2050?” The calculation process is the same as finding your current age: compare the birth date to the target date. The only difference is that instead of today’s date as the reference point, you substitute the date you’re interested in.

For example, suppose someone was born on March 4, 2005, and they want to know their age on January 1, 2050. The result would be 44 years, 9 months, and 28 days.

The same principle works in reverse. If you came across an old photo or diary entry and are wondering how old you were on that day, you can enter that past date instead of today’s. The tool will instantly show you the exact age you had then, and even tell you the total days.

How to Calculate Age from Birthdate in Excel

You can calculate or track age in Excel for data analysis, research projects, or to keep personal records. Excel offers built-in formulas that can replicate what a calculator does.

Here are the most useful formulas:

1. Age in Years: Use the DATEDIF function to calculate years between a birthdate and today.
   =DATEDIF(A1, TODAY(), “Y”)
   If the birthdate is in cell A1, this formula returns the completed years since that date.
2. Age in Months: To calculate the number of months since the last birthday:
   =DATEDIF(A1, TODAY(), “YM”)
3. Age in Days: To find the remaining days other than the full months:
   =DATEDIF(A1, TODAY(), “MD”)
4. Combine Years, Months, and Days: You can join the three results into a single readable output:
   =DATEDIF(A1, TODAY(), “Y”) & ” years, ” & DATEDIF(A1, TODAY(), “YM”) & ” months, ” & DATEDIF(A1, TODAY(), “MD”) & ” days”
   The result will be like: “25 years, 3 months, 12 days.”
5. Future or Past Age: Replace TODAY() with another date to calculate the age at that time. Let’s say you like to see how old someone will be on January 1, 2050. Enter:
   =DATEDIF(A1, DATE(2050,1,1), “Y”)

Excel gives you control over large datasets, so when you manage student records, employee data, or historical timelines, these formulas can be a great help for you.

Frequently Asked Questions

Can age calculator tell me the exact time I was born?

No. The calculator assumes your age starts from midnight on your date of birth. To include hours and minutes, you would need to know the exact time you were born and adjust the calculation manually.

Why does my age in months sometimes is different than I expect?

Months vary in length, like some have 28, 29, 30, or 31 days. When the calculator measures months, it counts from a specific day in one month to the same day in the next. If that date doesn’t exist (for example, February 30), the calculator adjusts based on actual month lengths.

Can this tool be used for legal age verification?

The age finder provides accurate results, but for legal purposes (such as ID checks, passports, or age restrictions), official documents like birth certificates should be used.

Does the calculator consider leap years?

Yes. Leap years are automatically included in the calculation, so the total number of days lived is completely right.

Can I calculate the difference between two random dates that aren’t birthdays?

Yes, you can enter any two dates, the start and end of the project, and the tool will show the difference in years, months, days, or whichever unit you choose.

Is there a quick way to estimate someone’s age without an age calculator?

You can always do a quick mental math by subtracting the birth year from the current year. It’s fast but only approximate, as the exact result depends on whether the birthday has already happened that year. For precise answers down to months or days, the calculator is the safe option.