Birthday Calculator

Find your exact age, next birthday, zodiac sign, Chinese zodiac, and fun birthday facts in one click.

Calculate your birthday facts

Use your real birthday or test any date.

Default is today. Change to see your age on any date.

What this birthday calculator shows

This birthday calculator goes far beyond a simple age counter. It uses your date of birth and an optional reference date to compute:

  • Your exact age in years, months and days
  • Your age in total days, hours and minutes
  • The day of the week you were born
  • The date and weekday of your next birthday
  • How many days are left until your next birthday
  • Your Western zodiac sign and Chinese zodiac animal
  • How many birthdays you have already celebrated

How age is calculated

Age is the difference between the reference date and your date of birth. The calculator uses calendar arithmetic, which is how age is normally counted in real life.

1. Age in years, months and days

To get the familiar years–months–days format, we:

  1. Subtract the birth year from the reference year.
  2. Subtract the birth month from the reference month.
  3. Subtract the birth day from the reference day.

If the day or month difference is negative, we “borrow” from the next higher unit:

  • If days < 0, subtract 1 month and add the number of days in the previous month.
  • If months < 0, subtract 1 year and add 12 months.

This method respects different month lengths (28–31 days) and leap years.

2. Age in days, hours and minutes

For total days, we take the difference in milliseconds between the two dates and divide:

\(\text{days} = \left\lfloor \dfrac{\text{refDate} - \text{birthDate}}{1000 \times 60 \times 60 \times 24} \right\rfloor\)

Then:

  • hours = days × 24
  • minutes = hours × 60

How the next birthday is found

The next birthday is the first occurrence of your birth month and day that is on or after the reference year.

  1. Start with the reference year and your birth month/day.
  2. If that date is earlier than the reference date, move to the next year.
  3. The difference in days between the reference date and that future date is “days until next birthday”.

For people born on 29 February, the calculator treats 28 February as the birthday in non‑leap years so that you still get a meaningful “next birthday” every year.

Western zodiac sign ranges

The calculator assigns your Western zodiac sign based on your birth month and day using the standard ranges:

  • Aries: March 21 – April 19
  • Taurus: April 20 – May 20
  • Gemini: May 21 – June 20
  • Cancer: June 21 – July 22
  • Leo: July 23 – August 22
  • Virgo: August 23 – September 22
  • Libra: September 23 – October 22
  • Scorpio: October 23 – November 21
  • Sagittarius: November 22 – December 21
  • Capricorn: December 22 – January 19
  • Aquarius: January 20 – February 18
  • Pisces: February 19 – March 20

Chinese zodiac cycle

The Chinese zodiac repeats every 12 years. This calculator uses your birth year to assign one of the following animals:

  • Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog, Pig

Internally, we map your birth year into this cycle using modular arithmetic:

\(\text{index} = (\text{year} - 1900) \bmod 12\)

Common questions

Can I see my age on a specific date?

Yes. Set the reference date to any past or future date. The calculator will show how old you were or will be on that day, plus how many birthdays you had by then.

Does time of day matter?

This tool works with calendar dates only, not exact times. If you need sub‑day precision (to the hour or minute), you can approximate by assuming midnight on both dates.

Is my data stored?

No personal data is stored on the server. All calculations run in your browser, and you can clear everything with the Reset button.

Birthday calculator FAQ

What does this birthday calculator do?

It instantly shows your age in multiple formats, your next birthday, the weekday you were born, your zodiac signs and several fun statistics like total days, hours and minutes lived.

Can I use it for someone else’s birthday?

Absolutely. Enter any date of birth and, if needed, a custom reference date (for example, “How old will my child be on 1 September 2030?”).

Why is my age in years slightly different from days ÷ 365?

Because calendar years are not all 365 days long. Leap years add an extra day, and months have different lengths. The calculator uses exact calendar math, not a simple 365‑day approximation.

How accurate are the zodiac signs?

The Western zodiac ranges are the standard ones used in most references. The Chinese zodiac is based on the Gregorian year only; if you were born near Chinese New Year and need the traditional lunar‑calendar assignment, consult a dedicated Chinese astrology resource.

Can I embed this birthday calculator on my website?

You can link to this page from your site or share it with others. If you need a custom‑branded version, you’d typically have a developer adapt similar logic to your own design and stack.