About the Birthday Calculator
Birthdays are the one date everyone keeps track of, but a few questions come up again and again. How many days until my next birthday? What day of the week will it fall on — is it worth planning a weekend party? What day was I born on? What is my star sign or birthstone? And what happens if I was born on 29 February?
This birthday calculator answers all of them. Enter your date of birth and it counts down the days to your next birthday, shows the date and weekday it falls on and the age you will turn, tells you the weekday you were born, lists the weekdays of the following five birthdays, and gives your star sign and birthstone. You can count from today or from any other date.
How to Use the Birthday Calculator
Enter your date of birth.
Optionally, enter a date to count from. Leave it blank to count from today.
The countdown and details appear below.
How the Countdown Works
next birthday = this year's birthday, or next year's if it has passed
days to go = next birthday − today
turning = year of next birthday − birth yearIf today is your birthday, the countdown shows zero and wishes you a happy birthday.
Step-by-Step Example
Born 15 May 1990, counting from 29 September 2026.
15 May 2026 has already passed → next birthday 15 May 2027
Days from 29 September 2026 to 15 May 2027 = 228
Turning: 2027 − 1990 = 37The next birthday is Saturday 15 May 2027, 228 days away. The person was born on a Tuesday, and the following birthdays fall on a Monday (2028), Tuesday (2029), Wednesday (2030), Thursday (2031) and Saturday (2032). Their star sign is Taurus and their birthstone the emerald.
Why Birthdays Move Through the Week
A common year has 365 days: 52 weeks and one day. So a birthday moves forward by one weekday each year — Saturday one year, Sunday the next. When 29 February falls between two birthdays, the year has 366 days and the birthday jumps forward two weekdays. In the example, the birthday moves from Saturday in 2027 to Monday in 2028, because 2028 is a leap year. Over a 28-year cycle each weekday comes round four times, though not at even intervals.
Leap-Day Birthdays
Someone born on 29 February has a true birthday only once every four years — though century years not divisible by 400, such as 2100, are not leap years, so the gap can be eight years. In common years this calculator counts down to 28 February, the most common choice for celebrating; others prefer 1 March, and some countries' laws use one or the other for legal age. The chance of being born on 29 February is about 1 in 1,461.
Star Signs
Western astrology divides the year into twelve signs by the Sun's position. The usual dates are:
Aries 21 Mar – 19 Apr Libra 23 Sep – 22 Oct
Taurus 20 Apr – 20 May Scorpio 23 Oct – 21 Nov
Gemini 21 May – 20 Jun Sagittarius 22 Nov – 21 Dec
Cancer 21 Jun – 22 Jul Capricorn 22 Dec – 19 Jan
Leo 23 Jul – 22 Aug Aquarius 20 Jan – 18 Feb
Virgo 23 Aug – 22 Sep Pisces 19 Feb – 20 MarBecause the exact moment the Sun enters each sign varies slightly from year to year, people born on a boundary date may see either sign listed in different sources.
Birthstones
Each month has a traditional gemstone. The modern list used by jewellers is garnet (January), amethyst (February), aquamarine (March), diamond (April), emerald (May), pearl (June), ruby (July), peridot (August), sapphire (September), opal (October), topaz (November) and turquoise (December). Some months have alternatives — citrine for November, tanzanite or zircon for December, alexandrite or moonstone for June.
The Birthday Paradox
In a group of just 23 people, there is a better than even chance that two share a birthday. It sounds unlikely, but with 23 people there are 253 possible pairs, and each pair has a 1 in 365 chance of matching. With 70 people the chance exceeds 99.9 percent. It is a favourite illustration of how intuition misjudges probabilities.
Planning Ahead
Knowing the weekday of future birthdays helps with planning. Milestone birthdays — 18, 21, 30, 40, 50 — often call for bigger celebrations booked months in advance, and venues fill up fastest on Fridays and Saturdays. If a milestone falls midweek, you can see at a glance whether the nearest weekend is before or after it. The countdown is also handy for children, who often want to know exactly how many sleeps are left, and for anyone arranging a surprise party who needs to work backwards from the date.
Understanding Your Result
The headline is the number of days until your next birthday.
The date line gives the next birthday and the age you will turn.
The weekdays line gives the day you were born and the weekday of the next birthday.
The following years line lists the weekdays of the next five birthdays.
The star sign and birthstone line gives your sign and gem.
When Should You Use This Calculator?
Use it to count down to a birthday or plan a celebration.
Use it to find which future birthdays fall on a weekend.
Use it to discover the weekday you were born.
Use it to look up a star sign or birthstone for a gift.
Common Mistakes
Forgetting that this year's birthday may have passed. The countdown moves to next year automatically.
Assuming the weekday moves by one every year. Leap years make it jump by two.
Mixing up day and month. Enter dates as year-month-day.
Treating star-sign boundaries as exact. They can vary by a day.
Counting from the wrong date. Leave the "count from" box blank to use today.