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Is Arbitrage Betting Risk-Free? Seven Ways an Arb Loses Money in 2026

The quick answer

  • Risk-free: no. The math is riskless only once both legs are accepted at the prices you calculated and both settle under the same rules.

  • Execution risk: the second leg can move or get capped after the first is already down.

  • Void risk: one book can void its leg as an obvious error and leave the other leg riding alone.

  • Fee risk: placed live, the taker fee on a prediction-market leg takes 21% to 48% of the example arb's profit, depending on the venue. Placed pre-game on Novig, a straight trade carries no fee for maker or taker.

  • Settlement trap: a sportsbook refunds a voided player prop; Novig settles the same void at pre-news fair value, above or below your entry.

  • Account risk: in Massachusetts regulator data, bettors who beat the closing line are likelier to have limits cut.

Arbitrage is risk-free on paper only. The seven failures below are each priced from the same starting position.

What an arb is, in one example

You back both sides of a two-outcome market at different venues so that every result pays more than you staked. With Team A at decimal 2.10 (+110) and Team B at 2.05 (+105), the implied probabilities sum to S = 1/2.10 + 1/2.05 = 0.964. Under 1 means an arb exists before fees.

With $200 total, stake $98.80 on A and $101.20 on B. If A wins you collect $207.48, a $7.48 profit. If B wins you collect $207.46, a $7.46 profit. That's a 3.74% return on stake (1/S minus 1), which isn't the same as the 3.60% gap (1 minus S) some calculators display.

How we checked

Rules and fees come from each operator's own documents: DraftKings Sportsbook's general betting rules, Novig's help center and the Ludlow Exchange rulebook and filings behind it, and Kalshi's fee schedule. Limiting data comes from the Massachusetts Gaming Commission. Everything was checked on 7 October 2026. Team prices are illustrative.

1. The second leg moves or gets rejected

The first leg is accepted at 2.10. By the time you submit the second, B has dropped from 2.05 to 1.90, or the book rejects the slip and re-offers at the new price.

At 1.90 with the same $101.20, the arb is gone. A winning still pays +$7.48, but B winning returns $192.28 on $200 staked, a $7.72 loss. Walk away instead and you hold a naked $98.80 bet: +$108.68 if A wins, -$98.80 if it doesn't.

How to reduce it: place the leg most likely to move first, usually the stale price, and set your worst acceptable second price before you click. On a prediction market a limit order can't fill worse than your price; the Ludlow Exchange rulebook fills orders on an "or better" basis.

2. The book caps your stake

You place B first, $101.20 at 2.05. Then the sportsbook accepts only $40 of the $98.80 you wanted on A.

Now $141.20 is staked. An A win collects $84.00, a $57.20 loss; if B wins you'll collect $207.46 and make $66.26.

How to reduce it: place the leg at the venue most likely to cap you first. Capped first, you can resize: $40 on A at 2.10 pairs with $40.98 on B at 2.05, both outcomes return $84, and the profit is about $3 instead of $7.47.

3. Only part of your order fills

Say the B leg is on a prediction market instead: 207 contracts at 48.8¢ for $101.02, paying $207 if B wins. Only 120 contracts are resting at 48.8¢.

It happens on any order book, Novig's included; its fee page describes orders where "part of your order fills immediately and the rest fills later," and Ludlow's immediate-or-cancel orders cancel "any unfilled portion." With 120 contracts ($58.56) against $98.80 on A, A winning nets +$50.12 and B winning nets -$37.36.

Sweep the next 87 contracts at 52¢ ($45.24) and you're covered again. Total cost rises to $202.60 and profit falls to $4.88 or $4.40.

How to reduce it: check the size at your price before placing the other leg, and size the arb to what's resting.

4. The two venues settle differently

Both legs stand and the venues grade the result differently, most clearly on player props.

DraftKings voids bets on a selection that "does not Participate." Novig's NFL prop contract settles to Void if the player records no snap, and every Novig Void settles under its Fair Value Settlement rule, at a fair value calculated from the 30 minutes of trading before the news. Novig's help page calls it "a settlement, not a refund."

Hypothetical: $100 on Over at the sportsbook, 210 Under contracts at 48¢ ($100.80) on Novig. The player is scratched, so the sportsbook returns $100 and Novig's fair value for Under comes in at 45¢, paying $94.50, for a net of -$6.30. Had fair value landed at 51¢, the same position would net +$6.30.

How to reduce it: read both venues' void and participation rules before placing either leg.

5. One leg is voided as an obvious error

An arb depends on one price disagreeing with the market, and DraftKings' rules define an Error to include any bet at odds "meaningfully different" from what similarly situated US sportsbooks offered. Such bets are voided "irrespective of the bet being settled."

If the A leg is voided you get $98.80 back and hold $101.20 on B alone: +$106.26 if B wins, -$101.20 if it loses.

Under Ludlow's rulebook the exchange-side rule is narrower: a trade executed within 50 cents of fair value on a $1 contract stands outside extraordinary circumstances, and member review requests are due within 15 minutes.

How to reduce it: distrust a price far off every other book, or one that hasn't moved after injury news, which DraftKings also lists as an Error.

6. Fees and transfer costs eat the edge

Pre-game, Novig charges no fee to either side on straight trades, and its maker fee is $0 on every trade type. Live takers pay 0.03 x price x (1 - price) per contract. Kalshi's general taker fee is 0.07 x price x (1 - price), and its Professional Football Game series also charges makers.

Run the 207-contract B leg at 48.8¢ as a live take: about $1.55 on Novig and about $3.62 on Kalshi, or 21% and 48% of a $7.47 profit. Kalshi also charges up to 2% on card deposits, so funding $100 by card can cost another $2.

Recent deposits can be held before withdrawal on both venues, and Novig keeps funds in open positions in escrow until they close or settle.

How to reduce it: take prediction-market legs pre-game where possible, fund by bank transfer, and put every fee into S before calling something an arb.

7. The account gets restricted

A September 2025 memo from the Massachusetts Gaming Commission's sports wagering chief found that bettors who consistently beat the closing line "are more likely to have a lower stake factor." On average 0.64% of Massachusetts accounts were limited as of 10 December 2024, and 70.3% of those were cut to under 25% of the default.

Hypothetical: capped at $5 a bet, the same arb pays $0.38 ($5 at 2.10 against $5.12 at 2.05), so one $2 card-deposit fee costs more than five of those arbs return.

Novig isn't a counterparty to your trade; its fee page says you're "trading with other users, not against the house." Its operator, Ludlow Exchange, which the CFTC designated as a contract market on 16 June 2026, can still limit an account's trading privileges under its rulebook, with the reason given in writing and an appeal window of 28 days.

What to look for

  • Execution order: place the leg most likely to move or be capped first.

  • Executable size: check the size resting at your price before trusting the headline number.

  • Settlement match: confirm both legs void, push and count overtime the same way.

  • Error exposure: treat a price far from every other book as a void risk.

  • Fee structure: a venue with no fee on pre-game straights, nothing charged to makers and a published formula for the rest keeps the arithmetic predictable.

  • Net economics: include taker fees, deposit fees and escrow time before calling it an arb.

Frequently asked questions

Is arbitrage betting risk-free?

No. The profit is locked only if both legs are accepted in full at the calculated prices and settle under the same rules, and any of those steps can fail.

Where do I find good arbitrage bets?

Scanners such as OddsJam, BetBurger and RebelBetting list apparent arbs, and each alert still needs checking for size, settlement rules and fees.

What happens if one leg of an arb is voided?

You're left holding the other leg as a straight bet. In the example here that's $101.20 riding on one team.

Can a prediction market cancel my trade?

Yes, in narrow cases. On Novig, Ludlow Exchange's rulebook lets trades within 50 cents of fair value on a $1 contract stand outside extraordinary circumstances, and member review requests are due within 15 minutes.

Do sportsbooks limit arbitrage bettors?

Massachusetts regulator data says bettors who beat the closing line are more likely to have limits lowered. On average 0.64% of accounts there were limited as of December 2024.

Sources

All checked 7 October 2026.

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