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Ledger · Probability

Coin Flipper

A fair coin, a weighted coin, or a ledger of every flip. The bias slider lets you ask “what if the coin weren’t actually fair?”

How to use Coin Flipper

  1. Press Flip the coin. The coin spins for about two-thirds of a second and lands showing the result.
  2. Read the stats panel: Total flips, Heads and Tails with their percentages, and your Current streak.
  3. Want a weighted coin? Drag the Coin bias · P(heads) slider. 50% is fair; 70% means heads comes up 70% of the time on average.
  4. Scroll to The ledger to see every flip, newest first. Hover over a mark to see its flip number.
  5. Press Reset ledger to clear the count and start a new run.
01 · Real-world fits

Common use cases

  • Deciding who kicks off or picks sides when nobody has a coin in their pocket
  • Breaking a tie between two restaurants, two names, or any two options you can't choose between
  • Showing a class that 10 flips can easily go 7 to 3 while 200 flips settle close to 50%
  • Testing the gambler's fallacy by watching what follows a streak of five heads
  • Simulating a loaded coin at 60% heads to see how many flips it takes for the bias to show in the tally
  • Making a quick call on a video call or stream where everyone can see the result
02 · The honest pitch

Why Coin Flipper?

The coin always lands on the face that was actually drawn. The spin is calculated to finish on the real result, so the animation never contradicts the tally. The bias slider runs from 0% to 100% heads in 1% steps, which turns a coin toss into a quick probability experiment. Every flip stays in the ledger until you reset or leave the page, so you can scroll back to a streak instead of taking it on faith.

03 · Edge cases

Frequently asked questions

At the default 50% setting, each flip compares your browser's Math.random() to 0.5: below is heads, anything else is tails. Math.random() is a pseudorandom generator, not a physical process, but it is statistically even and has no lean toward either side. Each flip is independent of the one before. It is not cryptographically secure, which has no bearing on deciding who buys lunch.