Orders & simulated fills

## How a fill is priced

Prices come from the YES book. NO is its complement.

Buy YES   = YES best ask
Sell YES  = YES best bid
Buy NO    = 1 − YES best bid
Sell NO   = 1 − YES best ask

Your whole order fills at that one price, however large it is, so there is no price impact. You still cross the spread, as on any exchange, and the liquidity checks below keep it at 3¢ or less.

Open positions are valued at the price you could sell at, so your equity, drawdown and target track what you could actually exit for.

Perps fill at the same BBO, by direction:

Open long   = best ask       Close long   = best bid
Open short  = best bid       Close short  = best ask

An open perp is marked where it would close: a long at the best bid, a short at the best ask. A new position therefore starts down by the spread it crossed. Leverage is each market’s venue maximum, and a leveraged position is liquidated when a move against it wipes out the amount you put in.

## Liquidity checks

We only enable trading on markets with sufficient liquidity, to maintain the integrity of the results. Every entry, add and exit on Polymarket must pass two checks.

• The event holds at least $20,000 in liquidity. Bitcoin, Ethereum and Solana up-or-down markets are exempt.
• The order book has a spread of 3¢ or less, and at least $500 resting on each side within 5¢ of the midpoint.

Perps have their own checks on every open and close: a spread of 1% of the mid or less, and enough resting size within 0.5% of the mid to fill the whole position on both sides.

If a check fails, the trade is blocked until liquidity comes back.

## Your call and your size

On a prediction market you name your own probability. Your edge is that probability minus the price you pay. The ticket suggests a size at quarter Kelly from that edge and your bankroll, capped so that losing it can’t take you past your drawdown floor. You can type your own size instead.