Sportsbook Vig vs Prediction Market Fees: The Real Math on What You Save
Everyone says exchanges are cheaper than sportsbooks. Almost nobody shows the arithmetic, including the part where the answer is "it depends on how you trade." Here it is in dollars, at three realistic yearly volumes, with the assumptions on the table.
Two claims float around this corner of the internet. Sportsbook loyalists say the fee difference is trivial. Exchange evangelists say books charge triple. Both camps are arguing without a spreadsheet, so let's just build the spreadsheet.
We'll compare what one year of the same trading costs at a sportsbook versus on the two big exchanges, using each venue's actual published pricing as of July 2026, and we'll do it honestly, which means one early admission: the lazy way to use an exchange saves you some money, and the patient way saves you almost all of it. The gap between those two sentences is the real story.
What a sportsbook actually charges
A sportsbook's fee never appears on a receipt, because it lives inside the odds. The standard line on an even matchup is -110 on both sides: risk $110 to win $100 either way. If the game is truly a coin flip, your expected loss on every such bet is about 4.5 cents per dollar you put at risk. That is the vig: a built-in toll on every wager, paid whether you win or lose, invisible by design.
And -110 straight bets are the book's best pricing. Parlays, props, and boosted-looking exotics carry margins several times higher, which is why the hold sportsbooks actually report on their total handle lands far above the theoretical 4.5%; hold in practice ran about ten percent in 2025, per industry revenue data. If your betting year includes the fun stuff, your real toll is closer to those numbers. For this comparison we'll be conservative and score the book at its best behavior: 4.5% on straight bets only.
What the exchanges actually charge
Both platforms price trades with the same uncertainty-scaled formula, fee = coefficient × price × (1 − price), which peaks at 50¢ and shrinks toward the extremes. The coefficients, from the platforms' current schedules:
- Kalshi: takers 0.07 (1.75¢ per contract at 50¢); makers pay about a quarter of that (~0.44¢).
- Polymarket US: takers 0.06 (1.50¢ at 50¢); makers receive a rebate of 0.0125 (0.31¢ credited per contract).
"Taker" means you crossed the spread with a market order; "maker" means you posted a resting limit order someone else filled. That distinction, one tap versus a moment of patience, is the whole plot of this article. (Full platform detail: Kalshi fees · Polymarket fees.)
The year-of-trading table
Assumptions, stated plainly so you can adjust them: every position is a 50¢ contract (the worst-case price for exchange fees, so this table is tilted against the exchanges), held to settlement (one fee per position, no round trips), and the sportsbook is scored at its best-case 4.5% straight-bet vig. Dollar figures are your expected yearly cost of fees or vig on the stakes shown:
| Yearly stakes | Sportsbook (best case) | Kalshi, market orders | Kalshi, limit orders | Polymarket US, market orders | Polymarket US, limit orders |
|---|---|---|---|---|---|
| $1,000 | $45 | $35 | $9 | $30 | earns ~$6 |
| $5,000 | $227 | $175 | $44 | $150 | earns ~$31 |
| $10,000 | $455 | $350 | $88 | $300 | earns ~$63 |
Read the table left to right and the two internet claims both collapse:
The loyalists are half right. If you use an exchange exactly like a sportsbook, slamming market orders on coin-flip prices, you save roughly a quarter to a third versus the book's very best pricing. Real money, not a revolution.
The evangelists are half right too, about the wrong thing. The dramatic savings don't come from switching venues. They come from switching habits. The patient columns run 80% to more than 100% cheaper than the book, and the Polymarket US maker column isn't a fee at all; at $10,000 a year of resting-order volume, the rebate program hands you back about $63. A sportsbook has no equivalent of that column and never will, because the house's whole business is being the only counterparty. An exchange's business is volume, so it pays people who bring liquidity.
And remember the tilt we built in: at prices away from 50¢, exchange fees fall while the book's margin, especially on longshots, gets worse. The table is the exchanges' bad day.
The honest footnotes
Four things the table doesn't capture, cutting both directions.
Round trips double exchange fees. The table assumes you hold to settlement. Trade in and out, which is half the point of an exchange, and each leg is charged. A taker round trip at 50¢ on Kalshi is about 3.5¢ per contract. The fix is the same as everywhere else in this series: maker entries make round trips cheap, and on Polymarket US a maker leg actively offsets the taker leg.
The spread is a cost too. Crossing a 2¢ spread costs you a cent or two beyond the printed fee, on any exchange, in any market. Books have no spread, but only because they've pre-charged you more than one in the line. In deep game markets the spread is a cent or two; in thin ones it can dwarf the fee, which is why liquidity gets its own article.
Promos are real money for casual bettors. Books hand out signup bonuses and boosts; exchanges mostly don't. A light bettor who genuinely harvests promos can beat the table's book column for a while. The catch is the ceiling: promo value fades, and the moment you win consistently, books cut your limits, a problem exchanges structurally do not have (the full comparison).
The menus don't fully overlap. This math covers outcomes both venue types list: game winners, tournament markets, and similar. The book's six-leg same-game parlay has no exchange twin; if that product is why you bet, no fee table changes your venue.
What this means in practice
Three rules fall out of the arithmetic:
- Any switch saves something. Even the laziest exchange habit beats the book's best pricing on comparable markets.
- Limit orders are where the money is. The maker columns are the argument. If you learn one mechanical skill from this whole series, make it that one.
- Score your own year, not the average one. Take your rough yearly stakes, pick your honest column, and the table gives you a number. If your betting history is parlay-heavy, the book column for you starts near double what's printed.
The vig was always the quiet tax on being a sports fan with an opinion. It turns out to be optional.
Related reading: Kalshi fees explained · Polymarket fees explained · Prediction markets vs sportsbooks · Bid vs ask and setting orders
Educational information, not financial advice. Fee schedules and odds pricing change; verify current rates before trading. Prediction markets involve risk of loss, and their legal status varies by location and changes over time.