Heads or tails

Settle a debate, pick a movie, or just watch a coin spin. Fair odds every time.

Tap the coin or press Space
Ready

Tap the coin, press Space, or hit the button.

Your tally
0 flips
0
Heads
0
Tails
50% heads50% tails
Last 20 flips
Use it to decide something

What is this tool?

A coin flip is the oldest tie-breaker we have, and this one lives in your browser. Each toss comes from your device's cryptographic random generator, so there's no weighted coin, no secret favorite, and no memory of what came up last time. Use it to make quick decisions, teach a probability lesson, or settle who gets the last slice.

Call it
Turn on Call it first in settings to pick a side before the flip and keep score. Or leave it off and just flip.
Flip it
Tap the coin, press Space, or use the button. The toss, the spin and the landing are all real-time.
Watch the tally
Heads, tails, streaks and a running split show up on the right. Great for seeing odds play out.

The odds, in plain English

A fair coin is simple: two sides, equal chances. The surprising part is how streaks and long runs behave. Here are the ideas worth keeping in your pocket.

One flip
Heads 50%
Tails 50%

One chance in two for each side. Whatever happened before doesn't enter the maths.

"And" means multiply. Two heads in a row: ½ × ½ = ¼.
"At least one" means subtract. One or more heads in 3 flips: 1 − (½)³ = 87.5%.
How likely is a streak?
Chance of getting the same side every time, from a standing start.
1 in a row
1 in 2
2 in a row
1 in 4
3 in a row
1 in 8
4 in a row
1 in 16
5 in a row
1 in 32
6 in a row
1 in 64
7 in a row
1 in 128
8 in a row
1 in 256
9 in a row
1 in 512
10 in a row
1 in 1,024

Any one streak is unlikely, but over a long session something has to give: in 100 flips, a run of 6 or 7 is typical.

Watch chaos turn into 50/50
The line tracks the share of heads as the flips pile up. Early on it swings wildly. By a few hundred flips it settles near 50%. That's the law of large numbers: the average steadies, not because the coin "makes up" for the past, but because new flips dilute it.
0%50%100%1 flip10 100 1,000
After 1,000 flips this run sits at …% heads. Notice the log scale: the first 10 flips get as much room as the last 900.
Flips are independent
Five heads don't make tails 'due'. The coin can't count, so every flip starts from zero. Believing otherwise is the gambler's fallacy.
Small samples are noisy
Ten flips can easily give you 7 heads. That isn't a broken coin, just a short run. Trust the pattern only when the sample is big.
Expect a spread, not a split
In 100 flips you'll land between 40 and 60 heads about 96% of the time. Exactly 50 happens only about 8% of the time.
Real coins aren't perfect
Researchers found that a coin caught in the hand lands on the side it started on about 51% of the time. A thick coin can even land on its edge, roughly 1 in 6,000 tosses for a nickel.

A short history of leaving it to chance

  1. Around 600 BCE
    Lydia mints some of the earliest coins. Once money has two faces, a two-outcome game is only a matter of time.
  2. Ancient Rome
    Romans flipped for "navia aut caput": ship or head, after the designs on their coins.
  3. Medieval England
    The call was "cross or pile", named for the cross stamped on one side of the coin.
  4. 1845
    Two settlers in Oregon tossed a copper penny to name their new town. Portland beat Boston.
  5. 1903
    Wilbur and Orville Wright flipped a coin at Kitty Hawk to decide who would try first. Wilbur won, and his attempt failed. Orville made history days later.
  6. 2007
    Mathematicians Persi Diaconis, Susan Holmes and Richard Montgomery showed a caught coin favors its starting side by about 51%.
The marathon flippers
Some people flipped coins for thousands of rounds just to check the maths. They all landed close to the middle line.
Count Buffon, 1700s2,048 heads in 4,040
50.69% heads
Karl Pearson, early 1900s12,012 heads in 24,000
50.05% heads
John Kerrich, 1940s (in an internment camp)5,067 heads in 10,000
50.67% heads

Sports, too: from football kickoffs to cricket innings, a coin decides who goes first because both sides get exactly the same chance.

Why your brain argues with the coin

Humans are pattern-hunters, and a coin is pure randomness. That mismatch produces some famous mistakes.

Which sequence looks more random?
Most people point at the first one.
HTHHTHTTHT
Chance: 1 in 1,024
HHHHHHHHHH
Chance: also 1 in 1,024

Every exact sequence is equally likely. We just notice the tidy ones. Genuinely random flips clump together more than our intuition expects, and we mistake that clumping for a "hot streak" or a rigged coin.

The gambler's fallacy
After a run of heads, tails feels overdue. It isn't. The coin has no memory and no sense of fairness over time.
The coin as a mirror
A big online study by economist Steven Levitt had people let a coin settle real dilemmas. Those who ended up making the change tended to be happier six months later. Often the flip's real job is to show you what you were hoping for.
Try this: flip, and before the coin lands, notice which side you're rooting for. If you're hoping for heads, you've already decided. The coin only delivered the news.