Where the price comes from

Up or Down on the same coins and the same windows also trades on the wider market. We take the live market price of each side and add our margin: 4% for both sides together, that is 2% on each side.

The price is shown in percent: "UP 43%" means a dollar of payout costs 43 cents.
The odds are 1 / price: 43% gives x2.33.
Payout = stake / price, rounded down to the cent. Your stake is included in it.

Example

The card shows UP 43% · x2.33. A $10 stake on UP pays $23.25 if UP wins (10 / 0.43): $13.25 of net profit. If DOWN wins, the $10 is lost.

The odds are fixed when you bet

Prices on the card move with the market while the window is open. Your bet keeps the price at which it was accepted: the payout you saw when confirming is the payout you get if you win, whatever happens to the price later.

Why a side can cost more

When many bets in a window are on one side, that side can get a little dearer.
A side that would cost more than 99% is not offered: the outcome is all but decided.

If the price moved while you were confirming, see why the odds changed.

Large stakes and the end of the window

The price comes from the market's order book: what that side costs to buy. A large stake is priced over the depth it needs, so its odds can be a little lower than the card shows; you see them before you confirm.
Over the last 30% of the betting time the margin grows, up to 2 times the usual one at the close.