Introduction
This Birth Date Calculator tells you your exact age from your date of birth. Type in the day you were born, and it shows your age in years, months, and days. It also shows your age in total months, weeks, days, hours, minutes, and seconds.
You can pick any "as of" date, not just today. That lets you find out how old you were on a past date, or how old you will be on a future one.
The tool also shows fun facts about your birth date, like the day of the week you were born, your star sign, your Chinese zodiac animal, your birthstone, your birth flower, and your generation. You get a countdown to your next birthday, a list of milestone birthdays with the dates they land on, and a step-by-step look at how the math works.
How to use our Birth Date Calculator
Enter your birth date and pick the date you want to measure from. The calculator then shows your exact age in years, months, and days, plus your total days, hours, and seconds, your birthday countdown, your zodiac signs, your generation, and fun birth date facts.
Date of Birth: Type or pick the day you were born, using MM/DD/YYYY. The year must be 1800 or later, and the date cannot be in the future.
Calculate Age As Of: This starts as today's date. Change it to any past or future date to see how old you were, or will be, on that day. It must come on or after your birth date.
Calculate: Click this button to update all results. You can also just press Enter after you change a date.
Reset: Click this to clear your dates and start over with the sample birth date and today's date.
What Your Birth Date Tells You
Your birth date is a fixed point in time. Everything else about your age is measured from it. Age is the gap between that day and another day, usually today. That gap can be shown in years, months, days, hours, or even seconds. They all describe the same span of time, just in different units.
How Age Is Counted
Most countries count age the same way. You are 0 the day you are born. You gain one year each time your birth month and day come back around. So a person born on May 22, 1990 turns 36 on May 22, 2026, not before.
To get an exact age, you subtract the day, month, and year separately. If the day or month comes out negative, you "borrow" from the next unit up, just like in regular subtraction. That is why an age can be written as something like 36 years, 2 months, and 30 days.
Why Leap Years Matter
A normal year has 365 days. A leap year has 366, because February gets a 29th day.1 Leap years happen in years divisible by 4, except century years that are not divisible by 400.2 That is why 2000 was a leap year and 1900 was not.2 Because of leap days, one calendar year averages about 365.2425 days.2 That average is used to turn total days into decimal years.
People born on February 29 have a birthday on that date only in leap years. Most calendars and laws treat February 28 (or March 1) as their birthday in other years.
Calendar Facts About Your Birthday
- Day of the week: The weekday you were born on. It shifts by one or two days each year.
- Day of the year: January 1 is day 1, December 31 is day 365 or 366. Astronomers use a related count shown by the Julian Date Calculator.
- Week number: The ISO 8601 standard splits the year into weeks 1–52 or 1–53, with each week starting Monday.3
- Quarter: The year is cut into four 3-month blocks, Q1 through Q4.
Generations
Your birth year places you in a generation, a group of people who grew up in the same era. Common labels are the Silent Generation, Baby Boomers, Generation X, Millennials, Generation Z, and Generation Alpha. These year ranges are not official. Different researchers set the edges a year or two apart.
Zodiac Signs, Birthstones, and Birth Flowers
The Western zodiac has 12 signs tied to date ranges, like Taurus from about April 20 to May 20. The Chinese Zodiac Calculator uses a 12-year animal cycle instead, so your animal comes from your birth year. Each month also has a traditional birthstone and birth flower. These are cultural traditions, not science, but they are a fun part of a birth date.
Milestone Birthdays
Some ages carry real meaning. Age 13 starts the teen years. Many places allow driving near 16 and treat 18 as adulthood. In the United States, citizens eighteen years of age or older have the right to vote.4 The national minimum drinking age is 21.5 Ages 30, 40, 50, and 65 are common markers for career, retirement, and health planning. Knowing how many days away a milestone is helps with planning parties, savings, and paperwork.
Where Age Really Matters
Exact age is needed for school enrollment, sports age groups, passports and visas, insurance quotes, medical dosing, retirement benefits, and legal forms. In these cases a rough guess is not enough. The count must be right down to the day.