FREE TOOL · READ-ONLY
Polymarket Slippage & Trading Cost Calculator
Load a BTC 5-minute market snapshot or enter your own book. Compare budgets, estimate costs and share the result.
No account · Read-only snapshots · No orders or wallet connection
MODELED RESULT · NOT AN EXECUTION QUOTE
Load a snapshot or use manual inputs to begin.
Saved inputs stay on this device. Sharing a link includes its inputs and snapshot. Shared results are historical, not verified live quotes.
Compare budgets on the same book
How the calculation works
- Sort asks from lowest price to highest.
- At each level, spend the smaller of the remaining budget and price × available shares.
- Divide that spend by the level price to obtain shares.
- Stop at the budget limit or the last supplied level.
Average price = purchase cost excluding fees / total shares.
Slippage (%) = (average price / best supplied ask − 1) × 100.
Slippage is relative to the best supplied ask, not a prediction or the bid–ask spread.
Estimated taker fee per level = shares × rate × [p × (1 − p)]^exponent, rounded to 5 USD decimals. Total-budget mode includes these fees; target-shares mode estimates the cost of the requested quantity. A price cap excludes more expensive levels. Fee parameters come from market metadata or your explicit assumption; unknown is never zero.
Official fee method · Actual per-match rounding, minimum size and order constraints are not simulated.
Worked example: $100 across two levels
The default book supplies 100 shares at $0.50 and 80 shares at $0.625.
- Level 1
- 100 × $0.50 = $50
- Level 2
- 80 × $0.625 = $50
- Total
- 180 shares · $100
Average price: $0.555555…; slippage: 11.1111…%. With a $120 budget, the same book leaves $20 unspent.
Read the full deep-versus-thin comparison →What this estimate includes
Calculations use a fixed ask snapshot and fractional shares, not a guaranteed execution. Fees are estimated per level when parameters are known. Real fees, tick sizes, minimum orders, rounding rules, cancellations and quote changes can alter execution. An incomplete book produces an incomplete estimate. This tool neither connects a wallet nor submits orders.
Polymarket’s official order-book documentation explains asks and displayed prices. Calculation and examples are PolyCerno analysis. Source checked 2026-09-15.
Slippage, fees and unfilled budget
How many shares can $100 buy?
It depends on the complete supplied ask ladder, not only the first price. The worked example gives 180 shares before fees; another book will produce another result. Select total budget to include known estimated fees.
Is slippage the same as a fee?
No. Slippage compares average purchase price with the best supplied ask. Estimated fees are shown separately. Unknown fees never become a zero-cost assumption.
What if the visible book is too small?
The calculator leaves the unsupported budget unspent. It does not invent deeper prices or guarantee an order will fill. Compare $10, $50, $100 and $200 on exactly the same snapshot.