Orders & simulated fills

## How a fill is priced

A perp order walks the live order book, the way a real order would. A buy takes the cheapest ask first, then the next level up, until your whole size is filled. A sell does the same down the bids. You pay the average price across the levels you took.

Buy $10,000, book asks:  $5,000 @ 100.00
                         $5,000 @ 100.20
Your fill                $10,000 @ 100.10 (average)

A small perp order fills at the top of the book. A large one moves further down the ladder and pays more, exactly as it would on the venue. If the book can’t fill your whole size, the order is refused rather than filled at a price that doesn’t exist.

Prediction markets fill at the top of the book instead, at one price for the whole order. Prices come from the YES book, and 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

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

A perp walks by direction:

Open long   = walk the asks       Close long   = walk the bids
Open short  = walk the bids       Close short  = walk the asks

An open perp is marked where it would close: a long at the bid, a short at the 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 order panel 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.