Where in π is your birthday?
Pi has infinitely many digits and they never repeat. Your date of birth is in there somewhere: find it and share it.
Interactive lab
Simulators to understand science and engineering by playing with them.
Projectile motion
Launch a projectile on Earth, the Moon or Jupiter. Animated trajectory, velocity vectors, range and maximum height.
Open simulatorSimple pendulum
Real simulation versus the textbook formula, with energy and a θ(t) plot.
Open simulatorColor code
From color to value and from value to color, for 4- and 5-band resistors.
Open toolRC circuit
Capacitor charging, cutoff frequency and Bode plot.
Open simulatorIdeal gases
Molecules in a piston: temperature, pressure and volume with PV = nRT.
Open simulatorOhm’s law
Voltage, current, resistance and power, with an animated circuit and a voltage divider.
Open simulatorDoppler effect
Animated waves, the sound of a passing siren and the Mach cone when you break the sound barrier.
Open simulatorYour age on other planets
How old you are on Mars or Jupiter, how many days you have lived and your next birthday on each planet.
CalculateMoney and finance
Calculators for your money, with charts that explain what is going on.
Take-home pay
From gross to net pay in the US, the UK, Germany, France, Italy and Spain, with taxes, social contributions and effective rate.
Open calculatorCompound interest
How much your savings grow with monthly contributions, and how much inflation eats away.
Open calculatorMortgage
Monthly payment, total interest and how much you save by overpaying a little each month.
Open calculatorFIRE calculator
How many years until financial independence based on what you earn, spend and save, using the 4% rule.
Open calculatorInflation calculator
What money from any year since 1960 is worth today, with official data for six countries.
Open calculatorRent or buy
Net worth year by year for both options and the point at which buying starts to pay off.
Open calculatorHow does the π search work?
The number π (pi) is the ratio of a circle’s circumference to its diameter. It is an irrational number: its digits never end and never follow a repeating pattern. It is believed, although not yet proven, that π is a normal number, which means that any sequence of digits appears somewhere in its expansion with the same frequency as any other.
This site contains the first 10 million digits of π and first searches for your date in DDMMYY format (for example, 14/03/95 → 140395). A 6-digit sequence appears, on average, once every million digits, so almost every date is found. If you like, you can also search for the full DDMMYYYY format; with 8 digits only about 10% of dates appear in the first 10 million.
The position is the digit at which your sequence starts, counting from the first digit after the “3.”. Pi Day is celebrated on 14 March (3/14 in US date format).
Frequently asked questions
Does my birthday appear in pi?
In DDMMYY format, almost certainly. A given 6-digit sequence appears on average once every million digits, and this site searches 10 million, so the chance that your date is missing is less than 1 in 20,000. In DDMMYYYY format, with 8 digits, only about one date in ten shows up.
How many digits of pi are known?
Using supercomputers and the Chudnovsky brothers’ algorithm, more than 100 trillion digits have been calculated, and the record keeps growing. Almost any practical use needs very few: NASA uses 15 decimals to navigate its probes through the solar system, and 40 would be enough to compute the circumference of the observable universe to within less than an atom.
Why does pi have infinitely many digits?
Because it is an irrational number: it cannot be written as a ratio of two integers, so its digits never end and never fall into a repeating pattern. Johann Lambert proved this in 1761. In 1882 Ferdinand von Lindemann also proved it is transcendental, which settled a 2,000-year-old problem: squaring the circle with ruler and compass is impossible.
Is my date sent to a server?
No. The digits of pi are downloaded to your browser and the search runs on your own device, so the date you type never leaves it. There is no sign-up either: it is only shared if you choose to share the result.