Enter a date of birth and any second date, past or future, and this calculator gives the exact age on that date in years, months and days. It also shows the total days, weeks and hours, the next birthday counted from the date you picked, the weekday of both dates, zodiac signs and a table of milestone dates such as your 10,000th day. People use it for school cut-off dates, eligibility checks, retirement planning and family history, anywhere a form asks how old someone was, or will be, on one specific date.
A sample birth date is prefilled so you can see how the result looks. Replace it with your own dates. Everything runs in your browser; nothing is sent or stored.
Age Certificate, AgoCalc
Enter a date of birth to see the exact age.
- Decimal age
- Next birthday (from your chosen date)
- Born on a
- Your chosen date is a
- Western zodiac
- Chinese zodiac
Milestone dates
| Milestone | Date | Measured from your chosen date |
|---|
Uses the date of birth above. Handy for licences, pensions and eligibility dates.
How to Use This Calculator
Step 1: Enter the date of birth
Use the calendar picker, or type the day, month and year into the three boxes. The picker and the boxes stay in step with each other, so use whichever suits your device. If you know the time of birth, adding it sharpens the live totals when the second date is today.
Step 2: Enter the second date
The field labelled Age on this date starts on today. Change it to any date you like, past or future. The preset buttons jump to common choices in one tap: today, a school cut-off on September 1, January 1 next year, or one year from today.
Step 3: Read the result
The answer updates the moment either date changes, with no calculate button to press. If the dates end up the wrong way round, the tool says so and offers a one-click swap. From the result panel you can copy the answer as text, print a simple age certificate, or copy a share link that carries the two dates.
Quick answer: age on a date equals the whole years up to the last birthday on or before that date, plus the whole months since that birthday, plus the remaining days. The sections below explain every figure the panel shows and the counting rules behind them.
What Your Result Shows
The headline figure is the exact age in years, months and days. Underneath it sit the same span expressed two other ways: total months with the leftover days, and total weeks with the leftover days. Forms ask for age in different formats, and a pension office, a school and a sports league rarely want the same one, so the panel gives all three readings from the same count.
The totals grid counts the whole span in single units: days, weeks, hours, minutes and seconds. The decimal age beside it divides the total days by 365.25, which produces the fractional figure that HR departments and insurers often use, such as 36.18 years. When the second date is today, the hours, minutes and seconds are measured from the actual time of birth or from midnight, and the seconds count up live.
The next birthday line is counted from your chosen date, and it gives the birthday's calendar date, weekday and distance in days, plus the age being turned. The panel also shows the weekday of the birth date, the weekday of the chosen date, the Western zodiac sign taken from the birth date and the Chinese zodiac animal taken from the birth year. For a child under two, a highlighted line leads with weeks and days, the way parents and health visitors usually describe a young child's age. Chinese zodiac years turn at the Lunar New Year, so a birth in January or early February may belong to the previous year's animal.
How Age Between Two Dates Is Calculated
The calculator walks the calendar the way a person counts on paper. It starts at the birth date and steps forward in whole years until it reaches the most recent birthday on or before the second date. From that birthday it steps forward in whole months, using the real length of each month, until one more month would pass the second date. The days left over after the last whole month complete the answer.
A short example shows the walk. For a birth date of 15 May 1990 and a second date of 20 October 2026, the most recent birthday is 15 May 2026, which makes 36 whole years. Five whole months run from 15 May to 15 October, and five days remain, so the exact age is 36 years, 5 months and 5 days. Every figure in the totals grid comes from that same span of 13,307 days.
Two calendar details decide whether the count is right. Months run from 28 to 31 days, and a whole month only counts once the same numbered day arrives again. When the starting day does not exist in a shorter month, the monthly anniversary falls on that month's last day, so a span starting on 31 January reaches its one-month mark on 28 February in a common year. February 29 is counted whenever it falls inside the span, which is why two four-year spans can differ by a day.
Shortcuts based on averages drift away from the calendar. Dividing the day count by 365.25 gives a fair estimate of the years, and this page shows that figure as the decimal age, but it can land a day out around birthdays and month ends because real months refuse to average out. The calendar walk avoids that drift by construction, and it agrees with the way registrars, schools and exam boards count age on their forms.
One convention is worth stating plainly: a person is 0 days old on the day of birth, and the total day count measures the full days that have elapsed since. Age in years turns at the start of the birthday itself, so someone born on 15 May turns 36 at the beginning of 15 May, in the time zone where they are.
Worked Examples
Every row in this table is calculated by the same engine as the tool above when the page loads, so the figures always agree with what the calculator will tell you. Press Load on any row to put those dates into the tool and explore from there.
| Date of birth | Second date | Exact age | What it shows | |
|---|---|---|---|---|
| 15 May 1990 | 14 May 2026 | Calculating... | One day short of a birthday. The age stays at 35 until the birthday itself arrives. | |
| 29 February 2000 | 28 February 2023 | Calculating... | A leap day birthday under the February 28 rule. With the March 1 rule the same dates read 22 years, 11 months and 27 days. | |
| 31 January 2023 | 1 March 2023 | Calculating... | A month-end start. February has no 31st, so the one-month mark lands on 28 February and one day remains. | |
| 8 June 2024 | 8 June 2024 | Calculating... | The same day twice. A baby on the day of birth is 0 years, 0 months and 0 days old. | |
| 14 March 1879 | 18 April 1955 | Calculating... | Age at death. Albert Einstein was born on 14 March 1879 and died on 18 April 1955. | |
| 3 November 2020 | 1 September 2026 | Calculating... | A school cut-off check. This child is still 5 on 1 September and turns 6 in November, which decides the school year in districts that apply a September 1 rule. | |
| 28 February 1900 | 28 February 2000 | Calculating... | A full century. The span holds 36,524 days because 1900 was not a leap year, while 2000 was. |
The February 29 row deserves a second look. On 28 February 2023 the February 28 rule says the person has just turned 23, while the March 1 rule says they are still 22, with a day to go. Neither answer is a mistake; they follow different rules, and the section below explains how to pick between them.
Leap Years and February 29 Birthdays
A year is a leap year when it divides by four, with one refinement for century years: a century year is a leap year only when it divides by 400. That is why 1900 had no February 29 and 2000 did. Roughly one person in every 1,461 is born on February 29, and their birthdays raise a question the rest of us never face: in a year with no February 29, which day completes another year of life?
Two answers are in wide use. Under the February 28 rule, the birthday completes on February 28 in common years, which matches the convention this site uses across its age tools. Under the March 1 rule, the birthday completes on March 1, on the thinking that the day after February 28 is where February 29 would have sat. Some legal systems treat March 1 as the legal birthday in common years, while many registries and software systems work with February 28.
The toggle above the result exists because the choice changes real answers. For one day each common year, the two rules disagree about whether a leap day baby has turned a year older, and that day can decide a licence application, an insurance start date or a school place. Set the toggle to the rule your form uses, and the panel shows the matching age, the matching next birthday and the matching milestone dates.
Age on a Specific Date: The Jobs People Use It For
School cut-off dates
Many school districts require a child to turn five by a fixed date, often September 1, to start kindergarten that year. The preset button above jumps the second date to the next September 1 so you can check a child against the cut-off in seconds. A child who turns five on September 2 waits a full year, which is why this single day matters so much to parents.
Exams, sports and eligibility
Exam boards set age limits that apply on one named date, and youth sports leagues group players by their age on a cut-off day rather than on the day of the match. Entering the official date as the second date gives the exact age the organisers will record, months and days included, which is the figure that settles borderline cases.
Retirement and pensions
Pension ages are reached on a date, and planning works better with the date than with a rough year. Use the second date to test any future year, then use the small tool under the result to work backwards: enter the age you want, such as 60, 65 or 67, and it gives the calendar date you reach it.
Weddings and big events
Couples check their ages on the wedding day, parents check a child's age on a moving date, and families check ages against visa and travel rules that apply on the day of travel. Setting the second date to the event date answers all of these in one step, weekday included.
Age at death and family history
For memorials, obituaries and family trees, enter the date of death as the second date and the result reads as an exact age at death in years, months and days. Genealogists use the same method to test whether two records can describe the same person, since a record that implies an impossible age usually points to a wrong date somewhere.
Which Calculator Do You Need?
Three questions sound alike and call for three different tools. If the question is simply how old you are right now, the age calculator answers it with one date of birth and no second date, because today is built in. This page exists for the second question: how old someone was, or will be, on one named date in the past or future, which is why its second date field carries equal weight.
Comparing two people is a different job. The age difference calculator takes two birth dates and returns the gap between the two people, with the older one named. And when no person is involved at all, the date difference calculator measures the span between any two dates for contracts, notice periods and project timelines, where the answer is a duration rather than an age.
Calculate Age Between Two Dates in Excel and Google Sheets
Spreadsheets carry a hidden function for this job called DATEDIF. Put the birth date in cell A1 and the second date in cell B1, and the three formulas below return the years, the months after the years and the days after the months, ready to sit side by side as an exact age. The function survives from early spreadsheet versions and works in both Excel and Google Sheets, even though it rarely appears in the formula menus.
=DATEDIF(A1,B1,"Y") whole years =DATEDIF(A1,B1,"YM") months after the years =DATEDIF(A1,B1,"MD") days after the months =B1-A1 total days
One caution from practice: the MD unit can return a wrong day count in a few month-end cases in older Excel versions, so cross-check any spreadsheet figure that decides something important against the calculator above. The totals row also shows why many people skip the formulas for quick checks, since total days needs nothing more than subtracting one date from the other.
Milestones and Fun Numbers
The milestone table in your result turns your two dates into a set of calendar landmarks. It lists the day you turn 1,000, 5,000, 10,000, 15,000 and 20,000 days old, the day you complete 1,000 weeks, the moment you pass 500,000 hours and the moment you pass one billion seconds. Ten thousand days works out to about 27.4 years, and a billion seconds to about 31.7 years, which is why so many people discover their billionth second has either just passed or is close.
Read the third column against your second date. Milestones on or before that date are marked as reached, with the date they happened, and later ones show the date they will arrive. Set the second date to a birthday or an anniversary and the table becomes a planner: it can tell a family that a child's 1,000th day falls three weeks before a holiday, in time to make something of it.
Frequently Asked Questions
Related Calculators
For your age at this moment, use the age calculator. To measure the gap between two people, use the age difference calculator. For the length of any span between two dates, with business days and inclusive counting options, use the date difference calculator.
Last updated: October 20, 2026. Reviewed by the AgoCalc editorial team. All ages are computed live in your browser with calendar-accurate month lengths and leap years.