What decides a BTC up or down round?

One public Binance BTCUSDT five-minute candle. The candle's open is the price to beat and its close decides the round. Up wins when the close is above the open. An exact tie refunds every bet.

When does betting close?

Ten seconds before the candle does. The last ten seconds of a round are settled, not traded.

How is the price of a side set?

From the chance that side wins, estimated from how far the price already sits from the price to beat, how long is left in the round, and recent volatility. A side costing 53 cents pays 1.00, so it returns about 1.89 times the stake.

What happens if Binance data cannot be read?

The round refunds everyone. There is no fallback price source, so a round whose candle cannot be read is not settled on anything else.

How a 5-minute BTC up or down round works

There is no random number generator here, and no result the house produces. A round is a public Binance candle. Everything below is a description of that candle and of what a side of it costs.

The round is a candle

Every five minutes Binance closes a BTCUSDT candle and opens the next one. That candle is the round. Its open is the price to beat; its close decides the round.

Up wins when the candle closes above its open.
Down wins when it closes below.
An exact tie — close equal to open, which does happen on a quiet five minutes — refunds every bet.

Neither number is ours to set. Both are published by the exchange, they are the same numbers every chart in the world is drawing, and you can pull them yourself: see verifying a round.

Betting closes early

Bets stop ten seconds before the candle closes. Those last ten seconds are what makes the result a settlement rather than a race against the clock, and they are the same ten seconds for everybody.

What a side costs

A side is priced like a share that pays exactly 1.00 if it wins and nothing if it does not. So its price is its chance — plus the house's spread.

At the default spread of 3¢, a coin-flip round has both sides at 53¢. Each pays 1.00, so each returns 1.8867× the stake. Buying both costs 1.06 to win 1.00, which is where the house's margin lives: about 5.7% of what is staked on a near-even round. It is a margin on turnover, not a win rate — the arithmetic is on its own page.

As a round runs the two prices move apart. Three minutes in, with BTC already $40 above the price to beat, Up is most of the way to winning and costs accordingly; Down gets cheap and pays a lot. The market is not guessing — it is reading how far the price has to travel in the time that is left.

How the chance is worked out

How likely the price is to end above where it started, given where it sits now, how long is left, and how violently BTC has been moving:

d      = ln(price / price to beat) / (σ · √seconds left)
chance = Φ(d) for Up, Φ(−d) for Down
share  = chance + spread
pays   = 1.00 / share

σ is recent volatility per √second, estimated from the exchange's own candle ranges and then kept current from live trades. When a side is priced, σ is moved 20% against that side — so a bad volatility estimate cannot be picked off for free by whoever notices it first.

The edges

A side is not sold above 99¢. Near the end of a round one side is usually all but decided, and there is no market in selling near-certainties for a cent.
Nothing pays more than 10×.
A bet is priced when it reaches the server, not on the screen it was clicked on. The client sends the worst multiplier it will accept, and a bet that would land worse is refused rather than filled.
A round whose candle cannot be read refunds everyone. There is no second price source to fall back on.

Every round is verifiable, and that is the whole point. You are not trusting a result — you are reading one off a public exchange. Here is how to check any round yourself.

Open the live market