Many traders compare their estimated probability directly to the market price and stop there. That is a useful first filter, but it is incomplete because the tradable break-even line usually sits above the displayed contract price once execution costs are included.

• Market price is only the starting probability reference.
• Break-even probability rises when fees and slippage rise.
• Flat costs matter most on smaller trades.
• A thin edge can disappear quickly after friction.

Start with the actual contract price you expect to pay and the size you are considering. Then add cost inputs that reflect the venue and workflow you really use, not the most flattering version of the trade.

1. Enter price, stake, and your estimated win probability.
2. Add fees, slippage, and flat cash costs.
3. Compare the break-even line with your estimated probability.
4. Check the maximum price your estimate can still justify.

Imagine a contract trades at $0.43 and you want to deploy $250. If you estimate the true win probability at 56%, the raw setup may look comfortably positive. But once fee rate, slippage, and fixed costs are included, the break-even probability moves upward.

• The buffer is more decision-useful than price alone.
• Maximum price helps with limit-order discipline.
• A trade can look good at one price and fail at a slightly worse fill.

The most common mistake is using your estimate but forgetting that execution has a cost. The second is feeding the tool a stake number that does not match the actual order you plan to send, which makes flat costs look smaller or larger than they really are.

• Comparing estimate to price but not to real break-even
• Ignoring fixed costs on small trades
• Using optimistic fee or slippage assumptions
• Treating a tiny buffer as if it were robust edge

Decision shortcut: If the probability buffer is small, assume your estimate is less precise than you want it to be. Thin buffers usually deserve smaller size or no trade at all.