FEE / MARGIN MODEL

Option C — pass-through fee model

Player order routes into Polymarket's book. Polymarket charges its own taker fee (embedded, not visible as a separate line to the player). Your platform fee is charged on top of trade value. Formula: polymarketFee = tradeValue × feeRate × (1 − price)

HOW POLYMARKET'S FEE ACTUALLY WORKS

Only takers pay (orders that fill immediately). Resting limit orders (makers) are never charged.
Each category has a fixed fee rate constant — but this constant is not the percentage actually charged. Crypto's "7%" is a rate used inside a formula, not 7% of every bet.
The real formula: effective % of bet = feeRate × (1 − price). This means the percentage you actually pay depends entirely on where the price sits:
— Near 50¢ (coin-flip): effective fee is about half the rate constant (e.g. crypto → ~3.5%)
— Near 1¢: effective fee approaches the full rate constant (e.g. crypto → ~7%)
— Near 99¢: effective fee approaches zero
Your platform fee stacks on top of this, so "2% + Polymarket's fee" is never a flat combined number — it moves with price. The bar chart below shows exactly what that looks like on a real bet.

FEE / MARGIN BY CATEGORY — drag the price slider

Your flat platform fee (%)

Enable small-bet surcharge tier

Bet size (trade value, USD)

Price (implied probability): 0.50

price 0.50 · bet size $100.00

PM = Polymarket's fee (bottom segment)

YOU = your platform fee (top segment)

Rates per Polymarket's published fee schedule (docs.polymarket.com/trading/fees) — Crypto 7%, Finance/Politics/ Mentions/Tech 4%, Economics/Culture/Weather/Other 5%, Geopolitics fee-free. Formula simplifies to tradeValue × feeRate × (1−price) since shares = tradeValue / price. This models the Polymarket-side fee only — does not include any vendor pass-through fee your SOW may add on top.