Trading Fees
PolySimulator mirrors Polymarket’s V2 taker fee schedule exactly. Fees
are simulated money (this is paper trading), but the economics are real:
every taker fill is debited the same fee a live Polymarket fill would pay,
so a strategy that is fee-unprofitable here is fee-unprofitable there.
Fees are not zero. A bot that models zero trading costs will compute
wrong PnL on every non-geopolitics market. Always read the fee field
returned on fills (OrderResponse.fee, /v1/account/history).
fee = C × feeRate × p × (1 − p)
| Symbol | Meaning |
|---|
C | Number of shares filled |
feeRate | The market category’s taker rate (table below) |
p | Fill price (0–1) |
p × (1 − p) factor makes the fee symmetric around 0.50—itpeaksthereandshrinkstowardthepriceextremes,soafillat0.99 pays a tiny
fraction of what the same share count pays at $0.50. Fees are rounded to 5
decimal places; the smallest charged fee is 0.00001 USD (amounts below that
round to zero). The amount actually debited from your balance is settled at
cent precision.
Worked example — 10-share BUY at $0.65 on a crypto market:
fee = 10 × 0.07 × 0.65 × 0.35 = 0.15925 USD
Category Rates
The schedule mirrors Polymarket’s published fee
table:
| Category | Taker fee rate | fee_rate_bps |
|---|
| Crypto | 7% | 700 |
| Economics / Culture / Weather / Other | 5% | 500 |
| Finance / Politics / Mentions / Tech | 4% | 400 |
| Sports | 3% | 300 |
| Geopolitics | 0% | 0 |
| Unknown / missing category | 5% (conservative fallback) | 500 |
curl "https://api.polysimulator.com/v1/fee-rate?token_id=7132104567925221..."
# crypto market → {"base_fee": 1000, "fee_rate_bps": 700}
# geopolitics market → {"base_fee": 0, "fee_rate_bps": 0}
base_fee mirrors Polymarket’s legacy base-fee parameter (observed
live: 1000 on fee-charging markets — sports, politics and crypto alike —
and 0 on fee-free markets). It tells you whether fees are enabled, not
the rate. Ported bots that read the PM field see byte-compatible PM
behavior.fee_rate_bps is the PolySimulator extra field carrying the effective
per-category taker rate actually charged, in basis points (the table
above). Use this one for fee math.
token_id is required, and errors mirror Polymarket’s live responses
verbatim: a missing or malformed token_id returns
400 {"error": "Invalid token id"}; a well-formed token that resolves to
no synced market returns 404 {"error": "fee rate not found for market"}.
Makers Pay Zero — Classified by Marketability
Matching Polymarket V2, takers pay the fee and makers pay nothing:
- Market orders, FOK, FAK/IOC — always taker.
- GTC limit orders that are marketable at placement (a BUY at/above
the live ask, or a SELL at/below the live bid) — taker. The order
crosses the book the moment you place it; the ~1-second matching-loop
latency doesn’t make it a maker. Swapping FOK market orders for
marketable GTC limits does not dodge the fee.
- GTC limit orders that genuinely rest (placed away from the touch and
filled later when the market moves into them) — maker, zero fee.
In addition to the marketability check at placement, any GTC fill that
happens within ~3 seconds of the order’s creation is classified as a
taker fill (the window is operator-tunable). An order that fills that fast
was effectively marketable when you placed it — the matching loop simply
took a cycle or two to get to it — so the few-second latency cannot be used
to dodge the fee. Orders that rest longer than the window before filling
keep maker (zero-fee) treatment.
Partial fills follow Polymarket’s split treatment: the slice that crosses
the book when your marketable order arrives pays the taker fee, while later
fills of the resting remainder are maker (zero-fee).
fee_rate_bps on /v1/data/trades rows reports the rate actually applied
to each fill: the category rate in bps for taker fills, 0 for fee-free
fills (maker fills, geopolitics markets, emergency exits).
Fee-Free Fills
| Case | Why |
|---|
| Maker fills (genuinely resting GTC) | Matches Polymarket V2 — makers never pay |
| Geopolitics markets | 0% category rate on Polymarket’s schedule |
| Emergency-exit fills | Break-even safety-valve exits on stuck/expired markets — charging would turn the recovery into a loss |
Documented Divergences from Polymarket
| Polymarket | PolySimulator | Why |
|---|
| Maker rebate (25% of taker fees; 20% on crypto) redistributed to makers | No rebate — makers simply pay zero | The rebate is PM’s redistribution of real collected fees; the simulator has no fee pool to fund it from |
Per-market feesEnabled flag — fees only charged on fee-enabled markets | Category schedule applied to all markets | The simulator doesn’t sync PM’s per-market fee flags (yet); the per-category schedule is applied uniformly |
Next Steps
