The Turnover Fee That Kills Most Prediction Market Strategies

A trading edge is the difference between your estimated probability and the price you pay, minus costs. Most traders spend their time trying to improve the first part and ignore the second. That is a mistake, because costs scale with turnover, and turnover is the one variable a trader fully controls.

The claim that a turnover fee "kills 90% of strategies" is a rule of thumb, not a measured statistic. But the arithmetic behind it is real: if your edge per trade is smaller than your all-in cost per trade, no amount of volume will make the strategy profitable.

What "turnover" means

Turnover is the total amount you trade relative to your capital. If you have a $1,000 bankroll and you buy and sell $1,000 of contracts ten times in a month, your monthly turnover is $10,000, or 10x.

A fee charged on turnover applies to each of those trades. A 1% fee on $10,000 is $100, or 10% of your bankroll. That is the number that matters, not the 1% headline.

On Polymarket, the explicit trading fee has historically been zero on many markets. That does not mean turnover is free. The costs are embedded in the spread, in slippage, in gas and in the difference between the midpoint and your fill. The fee documentation explains the current schedule.

The break-even math

Suppose a strategy wins 55% of the time on even-money contracts. The gross edge is 10% of stake per trade:

• Expected gross return = 0.55 × $1 - 0.45 × $1 = $0.10 per $1 staked.
• With a 1% cost per trade, the net edge is $0.09, or 9%.
• With a 2% cost per trade, the net edge is $0.08, or 8%.

That looks survivable. Now increase the frequency. If the strategy trades 20 times per month at full size, the annual turnover is 240x the bankroll. A 1% cost per trade becomes 240% of the bankroll per year. The gross edge of 10% per trade is applied to each trade, so the comparison is not 10% versus 240%; it is 10% per trade versus 1% per trade.

The key is the edge per trade, not the annualised edge. If the edge is 10% and the cost is 1%, the strategy survives. If the edge is 1.5% and the cost is 2%, it does not, no matter how many trades you make.

Why high-turnover strategies fail

Most short-term prediction-market strategies have a small edge. A momentum trade may capture 1-2 cents on a 50-cent contract. A mean-reversion trade may capture 1-3 cents. After the spread, the edge can be less than a cent.

A fee or spread of 1-2 cents per round trip can wipe out that edge entirely. The strategy looks profitable in a backtest that ignores costs and loses money in live trading.

This is why the "90%" claim feels true. A large share of retail strategies are high-frequency, small-edge strategies that cannot survive realistic costs. The exact percentage is unknown, but the direction is not.

The three costs that compound

Spread. The difference between the best bid and the best ask. If you buy at the ask and sell at the bid, you pay the spread twice.

Slippage. The difference between the midpoint and your actual fill. It grows with size and with thin liquidity. The liquidity guide explains how to measure it.

Explicit fees. Platform fees, copy-trading fees, gas and withdrawal costs. The copy-trading fee article shows how a 1% monthly fee can consume a 20% annual return.

Add them up and you get the all-in cost per round trip. That is the number to compare with your edge.

How to calculate your net edge

A simple formula:

• Estimate your probability of winning.
• Estimate the average payoff.
• Calculate gross expected value per trade.
• Subtract the spread, slippage and fees.
• Divide by the capital at risk.

If the result is less than 1-2%, the strategy is fragile. A small change in costs or market conditions can turn it negative.

A useful exercise is to compute the break-even win rate. For an even-money contract with a 2% cost, you need a win rate above 51% just to break even. With a 5% cost, you need above 52.5%. Small cost differences require large skill differences.

Which strategies survive

Low-turnover strategies with a large edge per trade survive best.

• Event-driven trades held for days or weeks, where the edge is a specific information advantage.
• Resolution mispricings, where the market misunderstands the rules.
• Niche markets with wide spreads, where a patient maker can capture the spread rather than pay it.
• Hedging and arbitrage, where the edge is structural and the costs are known.

High-turnover strategies can work, but they need a genuine speed or information advantage and institutional cost structures. A retail trader with a laptop is unlikely to have either.

The market-making article explains why speed matters in the high-turnover game.

A practical rule

Before you trade, write down three numbers:

1. Your estimated edge per trade.
2. Your all-in cost per round trip.
3. Your turnover per month.

If the edge is less than twice the cost, do not trade. If the turnover is high and the edge is small, reduce frequency or size. If you cannot estimate the edge, you do not have a strategy; you have a hope.

The trading journal guide helps you measure all three over time. The 2027 roadmap explains where durable edges come from.

The bottom line

Fees do not just reduce returns. They change which strategies are viable. A strategy that works in a zero-cost world can fail in a world with a 1% spread. Before you blame the market, check the cost line. It is often the difference between a good idea and a losing account.