Polymarket and Kalshi fees: maker vs taker.

The short version

Order-book exchanges (Polymarket, Kalshi, Betfair) charge fees on fills, not on the displayed price. The price you see on the order book is what some other trader is willing to fill at. By construction, YES + NO sum to 1.000. There is no overround baked into that price. The fee is a separate, explicit charge that comes off the trade according to the venue's current fee schedule. Maker and taker treatment can differ by venue, contract, and date, so confirm the published schedule before using a worked example for a live decision.

That's the whole story. The implications run through your edge math.

What maker and taker mean (order book primer)

An order book is a list of bids (buyers willing to buy at price X) and asks (sellers willing to sell at price X). When you place an order, you're either:

• Taking liquidity (taker), your order matches an existing resting order on the book and fills immediately. The venue's taker terms apply.
• Posting liquidity (maker), your order goes onto the book at a price the current book doesn't cross yet. It sits there until someone else's market order matches it. The venue's maker fee or incentive terms apply.

This is the same structure as crypto exchanges. Polymarket adopted it because Polymarket is a crypto-native exchange running on Polygon.

Use the current contract-specific fee schedule

Venue fees have changed over time and may differ by contract, order type, liquidity program, and jurisdiction. Check the venue's own current disclosure before sizing a position and enter that rate or formula in the calculator. Do not infer a fee from the displayed probability or reuse an old article's percentage as if it were a durable schedule.

Why this matters for your edge

On a sportsbook, the vig is baked into the displayed odds. When you bet −110 on both sides of a market, the implied probabilities sum to 104.76%. That 4.76% is the bookmaker's fee, embedded. When you devig the line to find fair, you've already accounted for the cost.

On Polymarket, the displayed price has no fee in it. The mid of the order book is the fair value some other trader is willing to fill at. Fees come off your fill separately. So your edge math runs in two stages:

Step 1: gross edge = (sharp_fair − polymarket_price) / polymarket_price
Step 2: net edge   = gross edge − taker_fee

In a hypothetical example, if your gross edge is +3% and the applicable fee is 2%, your net is +1%, still positive, still tradeable. If your gross edge is +1.5% and the fee is 2%, your net is negative. Don't take the trade.

The CLV.gg edge calculator ships this exact two-step math.

Worked example with explicit assumptions

You see Lakers championship YES priced at 0.28 on Polymarket. The CLV.gg sharp consensus says fair is 0.32. Your bankroll is $5,000 and you're considering a $500 fill. The 2% taker and 0% maker rates below are illustrative inputs, not a statement of current venue fees.

As a TAKER:
  Gross edge = (0.32 − 0.28) / 0.28 = +14.3%
  Taker fee  = 2.0%
  Net edge   = +12.3%
  Expected EV on $500 = $500 × 12.3% = +$61.50

As a MAKER (posted limit at 0.28, got filled):
  Gross edge = +14.3%
  Maker fee  = 0%
  Net edge   = +14.3%
  Expected EV on $500 = $500 × 14.3% = +$71.50

Posting as a maker captures another $10 of EV per $500 fill. Across hundreds of bets, that adds up to real money.

When to be a maker vs taker

Take when:

• The edge is large enough that you don't want to risk the price moving against you while your limit sits.
• The market is thin enough that posting an aggressive limit will sit unfilled for hours.
• You need the position now (event is imminent and you're sure).

Make when:

• The edge is marginal and the fee differential matters to your final EV.
• The market has decent volume so your limit will get hit reasonably soon.
• You're patient. A few hours of “did it fill?” is fine.

Optimal strategy for most users is a mix: make on marginal trades where the fee saved is meaningful, take on high-conviction bets where waiting risks the edge evaporating.

How an assumed exchange fee compares to sportsbook vig

In the illustrative 2% example, the assumed fee is smaller than the 4.76% overround in a two-sided −110/−110 sportsbook market. That does not prove an exchange fill is cheaper: the bid-ask spread, slippage, actual fee formula, and available price all affect the comparison.

The math is clean. The reason to keep retail sportsbook accounts open at all is line-shopping for a specific market that the exchanges don't cover yet, or because a sportsbook has the better executable price for that event (and the CLV.gg detector points you at supported offers).

What about Kalshi?

Kalshi uses its own published fee formulas, which should be checked for the specific contract and order. Convert the applicable fee to the same dollar or percentage basis as the estimated gross edge, then apply the same gross − costs = net pattern.

The takeaway

Exchange fees are not one durable universal percentage. Start with gross edge, subtract the venue's current disclosed fee, spread, and expected slippage, then decide. The edge calculator does this for one trade at a time. The live app does it for every edge it surfaces.