An attractive price is not an executable net return

A screen can show a favorable price while the trade available to you is unfavorable. The difference may be spread, insufficient depth, a stale quote, a fee or a contract rule. Analysis should describe a specific transaction at a specific size, not just a displayed percentage.

Price the cash flows of the contract you actually hold

Consider a hypothetical binary prediction contract that pays $1 for a winning outcome and $0 for a losing outcome. Buying 100 contracts at $0.48 costs $48 before fees. If your independent probability estimate is 52%, the expected settlement value is 100 × 0.52 × $1 = $52, giving $4 of expected net profit before costs. A quoted $0.48 price is a market-implied reference, not evidence that your 52% estimate is correct.

Suppose the entry fee for this hypothetical transaction is $1 and there are no other fees. Expected net profit falls to $52 − $48 − $1 = $3. The break-even probability rises from 48% to ($48 + $1) / $100 = 49%. These fee numbers are illustrative assumptions, not a current fee schedule for any venue.

If you intend to sell before resolution, the $1-or-$0 settlement calculation is not your trading return. Your exit price and exit fee matter. Buying 100 at $0.48 and immediately selling into a $0.46 bid loses $2 before fees, even if a mid-price or recent trade still displays $0.48.

The best ask is not the average fill

The expected settlement value remains $52 under your 52% assumption. With the same hypothetical $1 entry fee, expected net profit is now $52 − $51 − $1 = $0. A four-cent gross edge at the best ask disappeared when sized to the available depth. Calculate fees on the actual fills under the venue's rules; a flat fee assumption may not be valid.

A limit order can cap the price you accept, but cannot guarantee a fill. A marketable order may trade through several levels. A partial fill changes your exposure, and a resting order can be filled precisely when new information makes its price unattractive. Do not treat unfilled orders as completed positions in a backtest or ledger.

Fees are a rule, not a universal percentage

Venues can distinguish makers from takers, charge different markets differently, use price-dependent formulas, round fees, or change schedules. Some also have deposit, withdrawal, network or intermediary costs. A rebate is not earned merely because you submitted a limit order; its eligibility and realized amount need evidence.

Polymarket's official fee documentation explains market-specific taker fees and how to obtain fee parameters. Use the current rules for the exact market and order, rather than assuming every prediction market is fee-free or hard-coding one venue's schedule into another. This source is a rules reference, not a claim that Stakesift can execute trades or connect your account there.

Read resolution terms before comparing markets

• Definition: two titles can sound equivalent while using different cutoffs, data sources or definitions of the outcome.
• Timing: distinguish trading close, event completion, official determination and when funds become available.
• Exceptional cases: postponement, cancellation, disputed results or contract-specific invalidation may not behave like a normal win or loss.
• Collateral: capital tied up while waiting for resolution cannot fund another position. Borrowing or currency conversion adds separate costs if applicable.
• Access: jurisdiction, identity checks, limits and venue availability can make a displayed quote unavailable to you.

Complementary positions across venues are not automatically an arbitrage. You must verify that all outcomes and settlement rules truly align, both legs can be filled at the required sizes, and all costs are covered. Executing one leg before the other creates price and exposure risk. Even a fully matched economic payoff retains venue, operational and resolution risks; it is not a guarantee.

Keep quote, estimate and fill separate

Record the source and quote time, intended size, fee assumptions, allowed price, actual filled quantity and weighted average fill. Separate estimated EV at decision time from realized net result after settlement. A later price should not overwrite the price you actually paid.

Open the analysis workspace (signup required) for calculations using your inputs; Stakesift does not place wagers on your behalf. Read the probability and EV example for the estimate behind a gross edge, and bankroll reconciliation for keeping actual cash movements distinct from hypothetical returns. No calculation eliminates the possibility of losing your stake.