Spread

Also called bid-ask spread

The distance between the best bid and the best ask — the immediate cost of entering and exiting a position.

Because contracts pay a fixed dollar, spread is quoted in cents of probability and behaves as a direct tax on edge. Two cents wide on a 40¢ contract is a five percent round trip, which is larger than most edges anyone can honestly claim to have.

Prediction-market books run wider than equity books, and the reason is structural rather than a defect: most markets are small, short-lived, and quoted by a handful of participants who need compensation for the risk of quoting to someone who knows more than they do. Wide spreads cluster in exactly the places screens make look attractive — freshly listed markets, longshots priced under a nickel, and anything with no resting size behind the top level.

This is also why the cost model here never treats the sticker price as the price. Polymarket charges no trading fee, but the site still books roughly two tenths of a cent per share against every Polymarket leg, covering on-chain gas and an allowance for crossing a real spread. If a claimed edge does not survive an honest spread allowance, it was never an edge — it was a screenshot.

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Definitions describe how Polymarket and Kalshi behave and how WhaleTracks models them; venue rules and fee schedules can change, so confirm anything you size a position on with the venue itself. WhaleTracks is informational analytics, not financial advice. Past performance does not guarantee future results.