Flip a Coin: Heads or Tails Coin Toss

To flip a coin online, press Flip: the coin spins and lands on heads or tails, each with probability 1/2 = 50%. Flips are independent, so 3 heads in a row has probability 1/2 × 1/2 × 1/2 = 1/8 = 12.5%, and 10 heads in a row has probability 1/1,024, about 0.098%.

How to use the coin flipper

1. Press Flip the coin (or the space bar on the button). The coin turns over and lands on heads or tails.
2. To settle a choice, type what heads and tails mean, for example Pizza and Tacos. The winner appears next to the result.
3. Choose 10, 100 or 1,000 coins to flip a batch at once and see the counts, percentages and longest run.
4. Watch Your flips so far: running totals, your current streak, your longest runs and a chart of the heads percentage as it settles toward 50%.
5. Use Best of for a fair match of 3, 5 or 7 flips. After each flip it shows each side’s exact chance of winning from the current score.
6. Open Coin odds to work out exact chances, such as 7 in a row in 100 flips or at least 60 heads in 100, with the steps shown.
7. For a class, press Big screen. The coin and result fill the screen and stay readable on a projector. Press Escape to go back.

Is a coin flip really 50/50?

For this coin, yes. Each flip uses your browser’s crypto.getRandomValues(), which returns cryptographically strong random numbers. It draws a whole number from 0 to 4,294,967,295 and keeps the remainder after dividing by 2. That range holds 2³² numbers, an even count, so exactly half are even and half are odd. Heads and tails are equally likely, with no rounding bias.

Real coins come very close to 50/50, but not exactly. In a 2025 study in the Journal of the American Statistical Association, Bartoš and colleagues recorded 350,757 hand-tossed flips. The coin landed on the same side it started on 50.8% of the time (95% credible interval 50.6% to 50.9%). Heads and tails themselves came up equally often: the estimated chance of heads was 0.500. The bias depends on the starting side, so if you toss a real coin for something that matters, hide which side is up before you flip.

Probability of getting heads in a row

Each flip has a 1/2 chance of heads, and one flip does not change the next. To get k heads in a row from now, multiply 1/2 by itself k times: P = (1/2)^k = 1 ÷ 2^k.

This table answers “starting now, what are the odds?” Once you have already flipped 5 heads, the 6th flip is still 50/50. The coin has no memory. Believing that tails is “due” after a run of heads is called the gambler’s fallacy.

Streaks are more common than you think

A different question is whether a long streak shows up somewhere in many flips. That is much more likely, because a streak can start at any point. The table gives the exact chance of a run of at least r flips of the same side (heads or tails) somewhere in 20 or 100 flips.

In 100 flips, a run of 6 or more happens about 4 times in 5. That surprises most people. Try it in class: ask students to write down 100 made-up flips, then compare their longest run with 100 real flips from the tool. To find these numbers, count the sequences with no long run and subtract from the total. A sequence without a run of r is a row of blocks of length 1 to r − 1, so the count follows a simple recurrence. The Coin odds tab shows the full working for any number of flips up to 10,000.

Exact chance of k heads in n flips (binomial formula)

The number of heads in n fair flips follows a binomial distribution:

P(exactly k heads) = C(n, k) ÷ 2ⁿ, where C(n, k) = n! ÷ (k! × (n − k)!)

• n is the number of flips, so there are 2ⁿ equally likely sequences.
• k is the number of heads you want.
• C(n, k) counts the sequences with exactly k heads: the ways to choose which k flips are heads.

Example 1: exactly 2 heads in 4 flips. There are 2⁴ = 16 sequences, and C(4, 2) = 6 of them have two heads (HHTT, HTHT, HTTH, THHT, THTH, TTHH). So P = 6/16 = 3/8 = 37.5%.

Example 2: exactly 5 heads in 10 flips. C(10, 5) = 252 and 2¹⁰ = 1,024, so P = 252/1,024 ≈ 24.61%. Even the single most likely result happens less than a quarter of the time.

Example 3: at least 60 heads in 100 flips. Add C(100, 60) + C(100, 61) + … + C(100, 100) and divide by 2¹⁰⁰. The answer is about 2.84%, or about 1 in 35. The Coin odds tab does this sum exactly.

The law of large numbers, with your own flips

The more you flip, the closer the heads percentage gets to 50%. The gap in the count of heads and tails usually grows, though, just more slowly than the number of flips. The table shows the range that holds the number of heads in at least 95% of runs, worked out exactly from the binomial distribution.

The chart in the tool draws this range as a yellow funnel. Flip 1,000 coins a few times and watch your green line settle inside it.

Best of 3, 5 or 7

A best-of match is still fair: each side has a 1/2 chance of winning the whole match. What changes is how you get there. In a best of 3, the side that wins the first flip needs 1 more win, and the other side needs 2. The trailing side must win both remaining flips, a 1/4 chance, so the leader wins 3/4 = 75% of the time. If the first two flips are split 1–1, it is back to 50/50. The Best of tab shows these chances after every flip.

Deciding by coin toss

A coin toss is a fair way to break a tie between options you rate equally, such as who goes first or which of two restaurants to try. People often resist it, though. In studies published in Judgment and Decision Making (2010), Keren and Teigen found that people judged coin tosses fair, yet considered them inappropriate for many decisions, especially life-and-death ones. Using a concrete coin felt worse to participants than the abstract idea of a random choice.

Common mistakes with coin probability

• Treating tails as “due”. After 5 heads, the next flip is still 1/2 heads.
• Mixing up two questions. “10 heads in a row from now” is 1/1,024, but “a run of 10 somewhere in 1,000 flips” is about 62%.
• Expecting exactly half. Exactly 50 heads in 100 flips happens only about 7.96% of the time.
• Calling unequal results unfair. 58 heads in 100 flips is inside the normal range. Use the 95% range to judge a coin, not a single exact count.

Coin flip probability practice quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

Is flipping a coin really 50/50?

A virtual coin that uses an unbiased random source, like this one, is exactly 50/50. A real hand-tossed coin is very close: in 350,757 recorded flips, coins landed on the side they started on 50.8% of the time.

What are the odds of flipping heads 10 times in a row?

(1/2)¹⁰ = 1/1,024, about 0.098%, if you start counting now. The chance of seeing a run of 10 of either side somewhere in 1,000 flips is much higher, about 62%.

If I get 5 heads in a row, is tails more likely next?

No. Each flip is independent, so the next flip is heads with probability 1/2 and tails with probability 1/2, no matter what came before.

How many heads should I get in 100 flips?

About 50 on average, but anywhere from 40 to 60 is normal. That range covers about 96.5% of runs. Exactly 50 heads happens only about 8% of the time.

Is heads or tails more likely?

Neither. On this tool both have probability 1/2. With a real coin, the small bias found in the 2025 study is toward the side that was facing up at the start, not toward heads or tails.

Sources

• Bartoš, F. et al. Fair coins tend to land on the same side they started: Evidence from 350,757 flips (Journal of the American Statistical Association, 2025; arXiv 2310.04153)
• Keren, G. and Teigen, K. H. Decisions by coin toss: Inappropriate but fair. Judgment and Decision Making, 5(2), 83–101 (2010)
• MDN Web Docs: Crypto.getRandomValues() method

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