Skip to main content
Calibri’s trading cost is deliberately simple: one fee, charged once, when your order fills. There is no settlement fee, no redemption fee, and makers pay nothing.
  • One fee, at the trade — A single taker fee is charged the moment your order fills. Nothing is taken again at settlement — winners redeem the full 1.00 USDC per share.
  • Makers pay nothing — Only the taker (the side that crosses the book to fill a resting order) pays. If your resting order gets filled, you pay no fee — and you may even earn a maker rebate.

​
How the taker fee is calculated

The fee is not a flat percentage of what you spend. It scales with how uncertain the market is, peaking at price 0.50 and falling to zero at the extremes:
where P is the trade price (0–1), volume is the number of contracts, and rate is the taker rate for that market’s category. The P × (1 − P) term is a bell curve. It is 0 at the edges, rises to its maximum of 0.25 at a coin flip, and is symmetric about 0.50 — so:
  • You pay the most on coin-flip prices (near 0.50).
  • You pay very little on lopsided prices (near 0.05 or 0.95) — a near-certain outcome is cheap to trade.
  • The fee scales with your fill size.
This is the same formula Polymarket publishes.

​
Relative fee across prices

Holding rate and size fixed, the fee at each price relative to its maximum (at P = 0.50):
The curve is symmetric: P and 1 − P give the same value, so a trade at 0.30 and a trade at 0.70 carry the same fee.

​
Worked example

Buying 100 contracts of YES at 0.60 in a Crypto market (taker rate 7.00%):
Your stake is 0.60 × 100 = 60.00 USDC, so the fee works out to 2.80% of what you put in — below the headline rate, because the curve tops out at 0.25 and 0.60 is off the midpoint.

​
The fee is set aside when you place the order

The maximum fee your order could incur is reserved alongside your collateral the moment you place, so a fee is never taken out of the stake backing a contract. Anything left over is released when the order fills, rests, or is cancelled.
  • A limit order reserves the fee at its own limit price.
  • A post-only order reserves nothing — it can only ever be a maker, and makers pay no fee.
Practically: an order needs stake + maximum fee available, not just the stake. On the example above that is 60.00 + 1.68 = 61.68 USDC.

​
Taker rates by category

The rate is resolved per market: an event-specific override if one is set, otherwise the market category’s rate. A market whose category carries a 0.00% rate is free to take — no fee is charged and no rebate or referral reward is generated from it. The resolved rate is also carried in the market data the app reads, so the figure shown in the order ticket is always the one that will be applied.
Read the rate as the input to the formula above, not as a flat percentage of your stake. Because it is multiplied by P × (1 − P) — at most 0.25 — the effective cost is always a fraction of the headline rate, and smaller still away from the middle.

​
Where the fee goes

The taker fee is the only money the platform takes from a trade, and it also funds both reward programmes: The maker’s share is set per category — 20% in Crypto, 15% in Sports, 25% everywhere else. See Maker rebates for the full table. The referral share is likewise set per category and published in the rewards schedule — see the referral program. Both rewards are a percentage of the taker fee, not of your stake — so on the 1.68 USDC Crypto example above, the maker earns 0.20 × 1.68 = 0.336 USDC. Neither is paid at the moment of the trade: each fill records a reward, and a daily payout settles them. Markets in a 0.00% category generate no fee, and therefore no rewards.

​
Currency and rounding

  • All fees are denominated in USDC (6 decimals — one base unit is 0.000001 USDC).
  • The fee is computed from the formula, then converted to base units and rounded up. A fee smaller than one base unit rounds up to the minimum unit (or is skipped entirely when the rate is zero).

​
How the fee is collected

The fee is pulled on-chain from your Safe to the operator at settlement. Your Safe pre-approved this during setup, so you only ever sign — the operator pays the gas. See Self-custody for the full model.

​
What you are not charged

​
Deposits from other networks

Depositing USDC on Polygon is free, with no minimum. USDC you send to your Safe address on Ethereum, Base, Arbitrum or Optimism is bridged to your Safe on Polygon, and that bridge carries one fee. It is not a trading fee and is not shared with makers or referrers:
  • It covers network gas — the bridge transaction on the network you sent from, the delivery on Polygon, and, on your first bridge from a network, creating your Safe there.
  • At most 10 USDC, and at most 20% of the amount bridged. Both caps are fixed in the bridge contract; Calibri cannot raise them.
  • Above the cap only with your acceptance. When gas — mostly on Ethereum — costs more than the caps allow, the deposit waits and the Wallet page shows the fee it would cost now. You can accept it and bridge now, or wait: we bridge automatically at the standard fee once it covers the cost. A fee you accept is taken from that deposit and is non-refundable once the bridge is sent. See When Ethereum gas is high.
  • One fee per bridge. Below the network’s minimum — 20 USDC on Ethereum, 5 USDC on Base, Arbitrum and Optimism — deposits wait and are combined, then bridged together for one fee.
  • Taken before the bridge, in USDC, on the network you sent from. The rest is what arrives in your Safe on Polygon.
  • Circle charges nothing for its Standard transfers today. If that changes, Circle’s own fee comes out of the amount it mints on Polygon.
The Wallet page shows the current estimate for each network before you send. If anyone bridges your USDC before Calibri does — including you, which you can do at any time — no fee is charged on what they move. See Deposits from other networks.
Deposit on Polygon to avoid this fee. USDC sent on Polygon is credited directly, with no bridge, no fee and no minimum.

​
Withdrawals to other networks

Withdrawing USDC on Polygon is free, with no minimum. A withdrawal from your Safe to an address on Ethereum, Base, Arbitrum or Optimism goes through Circle’s bridge and carries one fee. It is not a trading fee and is not shared with makers or referrers:
  • It covers the cost — the transaction on Polygon and the delivery on the destination network — plus a margin.
  • At least 3 USDC to Ethereum, and at least 0.50 USDC to Base, Arbitrum and Optimism. There is no maximum: the fee follows gas on the destination network.
  • Shown before you sign. The withdraw form shows the fee and what you receive, and the fee is part of the transaction you sign. You are never charged more than that — if gas rises after you send it, we complete the delivery at our own cost.
  • Taken before the transfer, in USDC on Polygon. The rest is what arrives at your address.
  • Minimum withdrawals are 20 USDC to Ethereum and 5 USDC to Base, Arbitrum and Optimism.
  • Non-refundable once the withdrawal is sent.
See Withdrawals to other networks.
Withdraw on Polygon to avoid this fee. A withdrawal on Polygon has no fee and no minimum, and many exchanges accept USDC on Polygon.

​
In short

You pay a single taker fee when your order fills — never again at settlement. Makers pay nothing and earn a rebate. The fee is highest around 50/50 prices, near-zero on lopsided prices, and scales with your fill size. The rate depends on the market’s category (0%–7%).

Maker rebates

The share of this fee paid back to the maker, on the same curve.

Core concepts

Prices as probabilities and how settlement pays out.

Account fees endpoint

Read resolved fees programmatically in the API Reference.

Deposits from other networks

The bridge fee, minimums and timing for USDC sent on another network.

Withdrawals to other networks

The withdrawal fee, minimums and timing for USDC sent to another network.