Polymarket fees explained: the complete cost breakdown

The one-sentence fee summary

Polymarket trading is structurally free — the only real costs are spread and gas. Onramp and offramp via fiat partners are the friction points where meaningful fees appear.

Compared to:

Sportsbooks: 4–5% vig per bet (implicit)
Kalshi: a few cents per contract (explicit)
Traditional options broker: $0.65 per contract + broker fees

Polymarket is the cheapest among these for executing a trade. It's more expensive on the fiat onramp than Kalshi's ACH.

Every fee, itemized

1. Platform trading fee: 0%

Polymarket charges nothing on trades. This is the design of the exchange — users trade directly against each other, Polymarket operates the order-matching infrastructure, and fees go to oracle security and operations via minimal on-chain cost.

2. The spread

The spread is the difference between the best bid (highest buy offer) and best ask (lowest sell offer) on a contract.

Example:

Best bid: $0.48 (someone wanting to buy YES at 48¢)
Best ask: $0.51 (someone wanting to sell YES at 51¢)
Spread: $0.03

If you buy at market (take the ask), you pay $0.51. If you later sell at market (take the bid), you receive $0.48. Round-trip cost: $0.03 per contract.

Typical spreads:

Flagship markets (major elections, Super Bowl): 1–2¢
Second-tier liquid markets (primaries, sports during season): 2–4¢
Thin markets (obscure political, niche sports): 5–15¢

On $1,000 of YES at $0.50, you have 2,000 contracts. A 2¢ round-trip spread costs $40 — 4% of notional. Liquidity matters.

3. Polygon gas

Every trade requires a Polygon transaction. Typical gas cost: ~$0.005–0.02 per trade. Imperceptible at normal trade sizes.

If you use Polymarket's email signup, some gas costs are absorbed by Polymarket. If you self-custody via MetaMask, gas comes from your MATIC balance.

4. Fiat onramp (depositing)

Three onramp paths with different costs:

MoonPay card onramp (in-app): 3–5% fee on the fiat amount. Instant, KYC required once.

Exchange withdrawal (Coinbase, Kraken, Binance): Usually free or very low. Requires existing exchange account. Takes 5–30 min.

Cross-chain bridge from Ethereum USDC: Free on Polymarket/Polygon side. Costs $3–15 in Ethereum gas. For users with existing Ethereum USDC.

Direct wallet transfer from another Polygon wallet: Free aside from Polygon gas (pennies). For crypto-native users.

5. Fiat offramp (withdrawing to bank)

Onramper fiat offramp: Typically 1–3% fee. KYC required. Takes 1–3 business days.

Withdrawal to your own Polygon wallet: Free (pay ~$0.01 in Polygon gas). Then bridge/swap/cash out at your preferred venue.

6. The oracle security fee (tiny)

When a market resolves, a small portion of trade proceeds goes to UMA's oracle security pool. This is how the decentralized oracle is funded. Typical impact: a fraction of a cent per contract.

Real-world examples

Example A: Small casual trade

You buy $100 of YES on a liquid political market at $0.60.

Contracts: 166 YES
Platform fee: $0
Spread (if market order, ask was at $0.60, bid at $0.58): $0 on buy, $0.33 estimated sell
Gas: ~$0.01
Total round-trip cost (market orders): ~$0.34 out of $100

If market resolves YES: you receive $166, gross profit $66. Net $65.66 after costs. That's 0.5% friction — trivial.

Example B: Large trade on a thin market

You buy $10,000 of YES on a thin market at $0.30 with 10¢ spread (best bid $0.28, best ask $0.30).

Contracts: 33,333
Platform fee: $0
Spread: you could potentially eat through the order book for larger orders. Assume 2¢ average fill vs best ask.
Market-impact slippage: significant on thin books. Could cost 3–5% of notional.
Gas: ~$0.01

Total cost could be $300–500 out of $10,000. That's 3–5% friction — material. Use limit orders on thin markets.

Example C: First-timer funding via MoonPay card

You want to fund $500 via Polymarket's in-app card onramp.

MoonPay fee: ~$20 (4%)
You receive: $480 in USDC
Polymarket fees to trade: as above

Over $500, the $20 onramp fee dominates. For $100 deposits, it's $4. For $50, it's $2.

Example D: Crypto-native exchange funding

You have $500 USDC on Coinbase. Withdraw to Polymarket via Polygon:

Coinbase fee: $0 (as of current Coinbase terms)
Gas: ~$0.02 on Polygon
Total: $0.02

Then trade with a minimal per-trade fee, thin spread, pennies in gas. Total friction: a few dollars to deploy $500.

How Polymarket fees compare

vs Kalshi

Kalshi charges per-contract fees (a few cents per contract). On a $1,000 position with 2,000 contracts at $0.02/contract, you pay $40 round-trip. Similar order of magnitude to Polymarket's spread costs on liquid markets.

For small, infrequent trades: Kalshi's fee is modest. For large, frequent trades: Polymarket can be cheaper (smaller spread percentage).

vs sportsbooks

Traditional sportsbooks (DraftKings, FanDuel, Bet365) bake 4–5% vig into their odds. A $100 bet on NFL moneyline with standard juice is a ~4.5% implicit cost.

Polymarket's round-trip cost on the same event would typically be 0.5–2%. Polymarket is substantially cheaper on a per-bet basis.

vs options brokers

Trading options on Robinhood or Interactive Brokers: typically $0.65 per contract plus broker fees. On deep-ITM contracts, this is a small percentage; on cheap OTM contracts it's a big percentage.

Polymarket's 0% + spread is competitive for similar volume. For very small trades, Polymarket's spread can dominate.

Strategies to minimize fees

Use limit orders, not market orders

Market orders take the spread. Limit orders post your own price and avoid spread cost (though may not fill).

Onramp via exchange, not card

MoonPay's 3–5% is much more expensive than Coinbase's free withdrawal.

Don't over-trade

Each trade has some friction. A strategy that requires 100 round-trips per week is paying more friction than one with 10.

Size appropriately for liquidity

On thin markets, large orders hit increasingly worse prices as you eat the book. Either use limits patient enough to fill at good prices, or size smaller.

Leave fiat on fiat rails until final

If you're cycling in and out of fiat frequently, you're paying onramp + offramp fees repeatedly. Consider keeping your trading bankroll in USDC on Polygon between strategies to avoid unnecessary fiat conversion.

Fee-adjusted returns

For a serious trader, real edge is compared to round-trip cost:

If you trade in and out frequently and round-trip fiat each time, onramp/offramp fees alone can exceed 8–10% of your bankroll per year.
Keeping funds in USDC between trades reduces this to near-zero.
At the spread-and-gas level, frequent trading might cost 1–3% per year in friction on a reasonable trade cadence.

Your strategy needs to beat this friction to be profitable. Friction-aware traders always pay attention to how they're moving in and out of fiat.

FAQ

Frequently asked questions

Is Polymarket really free to trade?+

Platform fee is 0%. But you pay spread and tiny gas on every trade, plus onramp/offramp fees on fiat conversions. Call it "essentially free" rather than "literally free".

What's the spread on Polymarket?+

Typically 1–3¢ on liquid markets, up to 10–15¢ on thin ones.

How much does gas cost?+

~$0.01 per trade on Polygon. Negligible.

What's the cheapest way to fund Polymarket?+

Withdraw USDC from a major exchange (Coinbase, Kraken) to your Polymarket address on Polygon. Usually free or near-free.

What does MoonPay charge for Polymarket deposits?+

Typically 3–5% of the deposit amount. Check the exact fee on the deposit confirmation screen.

Is there a withdrawal fee on Polymarket?+

Free to your own Polygon wallet. 1–3% via Onramper fiat offramp.

Does Polymarket charge to cancel orders?+

No. Limit orders can be placed and cancelled without fee.

Are there hidden fees?+

A tiny oracle security fee (fraction of a cent) is deducted from resolution proceeds. Otherwise, no hidden fees — everything is on-chain and auditable.