Every venue, with its real cost
The number that matters at every venue is what it quietly charges you. Prediction markets publish explicit fee schedules; sportsbooks hide their cost inside the odds as overround (“vig”). We measure both — the fee schedules below come from the venues' published docs, and every sportsbook margin is computed from the live lines our scanner ingests, averaged over the last 7 days.
Prediction markets: published fee schedules
Both venues charge on trades, not deposits, and both price fees against p × (1 − p) — cheapest at extreme prices, most expensive at 50¢.
Kalshi
| Price | Position | Fee | Of stake |
|---|---|---|---|
| 50¢ | $500 | $17.50 | 3.5% |
| 10¢ | $100 | $6.30 | 6.3% |
The fee per contract peaks at 50¢ — but relative to money at risk, cheap contracts cost the most.
Polymarket
Sportsbooks: measured overround (vig)
Overround is the sum of a market's implied probabilities minus 100% — the venue's built-in cost on every two-way market. Lower is better pricing. Measured from 3,379,396 live two-way lines across 20 books over the last 7 days; pre-game US lines only.
| Sportsbook | Avg margin | Moneyline | Spreads | Totals | Lines sampled |
|---|---|---|---|---|---|
| LowViglowest margin | 3.80% | 3.04% | 3.68% | 4.30% | 108,867 |
| BetAnySports | 4.30% | 3.78% | 4.35% | 4.63% | 61,164 |
| Bovada | 4.44% | 4.17% | 4.47% | 4.64% | 155,331 |
| ESPN BET | 4.54% | 4.10% | 4.86% | 4.66% | 166,559 |
| BetOnline | 4.55% | 3.04% | 4.90% | 5.03% | 108,860 |
| DraftKings | 4.56% | 4.31% | 4.67% | 4.70% | 712,802 |
| Hard Rock Bet (FL) | 4.56% | 4.20% | 4.75% | 4.73% | 31,623 |
| FanDuel | 4.61% | 4.09% | 4.85% | 4.89% | 125,512 |
| BetUS | 4.66% | 3.31% | 4.71% | 4.83% | 246,805 |
| Fanatics Sportsbook | 4.73% | 4.52% | 4.89% | 4.78% | 91,967 |
| Hard Rock Bet (OH) | 4.78% | 4.87% | 4.73% | 4.74% | 47,442 |
| Hard Rock Bet | 4.88% | 4.45% | 5.32% | 4.85% | 94,874 |
| BetMGM | 4.94% | 4.49% | 4.61% | 5.55% | 145,166 |
| Betparx | 5.32% | 4.75% | 5.10% | 5.77% | 112,465 |
| Bally Bet | 5.37% | 4.80% | 5.16% | 5.81% | 112,410 |
| BetRivers | 5.53% | 5.03% | 5.37% | 5.91% | 112,428 |
| Caesars | 5.87% | 5.16% | 6.21% | 6.25% | 607,604 |
| MyBookie | 6.06% | 5.18% | 6.17% | 6.41% | 93,953 |
| Fliff | 6.30% | 5.64% | 6.57% | 6.60% | 61,249 |
| ReBet | 6.78% | 5.93% | 7.37% | 7.03% | 182,315 |
Methodology
Every 15 minutes our scanner pulls pre-game moneyline, spread, and totals prices for the sports we track. For each two-way market at each book we compute 1/odds₁ + 1/odds₂ − 1, drop frozen or malformed quotes, and store the average per book per cycle. The table shows the sample-weighted average of those measurements. Three-way markets and stale in-play lines are excluded. Prediction-market fee schedules are taken from the venues' published documentation and re-verified when venues announce changes.
These figures describe pricing, not quality: a low-margin book may limit winners, a high-margin book may have markets nobody else lists. Venue availability varies by state; you must be of legal age in your jurisdiction to use any of them. This page is reference data, not an endorsement or advice of any kind.
Why this matters for arbitrage
A cross-venue price difference only pays if it survives both venues' costs. That is exactly what our scanner checks, continuously, across every venue on this page — walking live order books, applying these fee schedules, and surfacing only differences with money left over. See it running on the live dashboard, or read how it works.