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Quick Answer

The prediction market with the lowest headline fee is not always the one with the lowest trading cost. Compare the exact market, your maker or taker status, the displayed fee, spread and expected average fill at your order size. Minimum fees matter most on small orders, while price impact can dominate larger orders. Because schedules change by platform, category and contract, there is no permanent “cheapest” venue. Use the live preview and current official fee pages for the trade you are considering.

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Key Takeaways

  • Headline coefficients are not the same as the fee shown on a trade.
  • Maker and taker orders can have different costs.
  • Spread and price impact can exceed the platform fee.
  • Minimum fees and rounding rules distort small-order comparisons.
  • A fair comparison uses the same event, rules, order size and execution type.
  • Opinion’s official fee facts are maintained on Opinion Fees Explained.

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The Cost Formula That Matters

Use this framework:
Funding-provider, bridge, network and withdrawal charges should be tracked separately because they may not appear in the trading-fee schedule.

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Five Inputs for a Fair Comparison

If any input differs, the comparison is directional rather than like-for-like.

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Maker vs Taker

A maker places an order that rests in the order book and adds liquidity. A taker executes immediately against available liquidity. A limit order is not automatically a maker order: if it crosses the book, the executed part can be treated as taker flow. Current policies differ by venue and market. The live order preview should determine which fee applies.

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Why Spread Can Matter More Than the Fee

Suppose the best bid is 0.48 and the best ask is 0.52. The four-cent spread is an immediate cost if you buy at the ask and sell at the bid. A platform with a low fee but a wide spread can therefore be more expensive than one with a higher fee and deeper liquidity. For larger orders, inspect several order-book levels. The top quote may cover only a small portion of the intended size. Read Order Books, Spreads and Liquidity for the mechanics.

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Why Minimums Distort Small Trades

A fixed minimum fee represents a larger percentage of a small order. For example, the same $0.50 floor is 10% of a $5 order but 0.1% of a $500 order before considering the rest of the formula. Do not extrapolate a small test order’s effective percentage to larger trades without recalculating.

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Current Official Sources

Use one official source of truth per platform: Our Polymarket vs Kalshi vs Opinion Fees page applies the same framework across the three commonly compared venues.

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A Repeatable Comparison Test

  1. Find equivalent contracts with equivalent resolution rules.
  2. Set the same intended order size.
  3. Record the best bid, best ask and depth.
  4. Enter the order without confirming and record the fee preview.
  5. Estimate the average fill across available levels.
  6. Repeat for the intended exit.
  7. Add external funding or withdrawal costs.
This produces a decision-quality comparison without relying on “lowest fees” marketing language.

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Where Opinion Fits

Opinion currently charges takers while makers are not charged under the published policy. Its exact fee depends on the market, price, discounts and minimum. Because these details can change, this page does not duplicate the full formula. Read the maintained Opinion Fees Explained page and verify the live order preview.

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What to Watch

  • Changes to category or contract-specific schedules.
  • Whether a limit order rests or executes immediately.
  • Minimum fee and rounding behavior.
  • Order-book depth at the intended size.
  • External network, bridge, funding and withdrawal charges.

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FAQ

There is no permanent winner. The answer depends on the exact contract, maker or taker status, price, size, minimums, spread and depth.
No. Maker policy varies by platform and sometimes by market. A limit order that executes immediately may also be charged as a taker.
No. Spread and price impact can be larger than the platform fee, especially in a thin order book.
Minimum fees and rounding rules represent a larger percentage of small orders.
Use Opinion Fees Explained, which links to the current official Docs and records the verification date.
Review it whenever a platform changes its schedule and before publishing any exact numeric comparison. The live order preview remains the final check.Educational information only. Prediction-market trading involves risk, and access varies by jurisdiction.

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Sources & References

  1. Polymarket — Trading fees — Current category-level fee structure and maker/taker treatment
  2. Kalshi Help Center — Fees — Current market-specific fee guidance
  3. Kalshi — Fee Schedule — Current formulas and contract-specific schedules
  4. OPINION Docs — Fees — Current maker/taker policy, range, formula and minimums
All sources verified 2026-08-13. Prediction-market terms change frequently — verify against each platform’s current documentation before treating these numbers as decision-quality data. Editorial content, not investment or gambling advice.