"Is the arbitrage calculator free to use?"

"Yes, the arbitrage calculator is completely free. Enter odds from any sportsbooks to detect arbs and see optimal stake splits instantly."

"What odds formats does the arbitrage calculator support?"

"The calculator supports American (moneyline), decimal, and fractional odds formats. Select your preferred format and enter odds from any sportsbook."

"How does the calculator determine if an arbitrage opportunity exists?"

"It converts all odds to implied probabilities and adds them together. If the total implied probability is below 100%, an arbitrage exists and the calculator shows optimal stake splits for guaranteed profit."

"Does the calculator account for platform fees?"

"Yes. You can enter a fee/commission percentage and the calculator adjusts payouts accordingly. Polymarket charges variable taker fees by market type (up to ~2% on general markets, higher on select crypto and sports markets), while sportsbook vig is typically built into the odds."

Arbitrage Calculator — Surebet & Arb Betting Calculator

Enter odds from different sportsbooks to instantly detect arbitrage opportunities. The calculator shows optimal stake splits for guaranteed profit and accounts for platform fees.

Odds Format

American Decimal Fractional

Outcomes

Sportsbook Outcome Odds Impl. Prob

Total Stake ($)

Fee / Commission (%)

How the Arbitrage Calculator Works

Step 1: Convert to Implied Probability

Every odds value represents a bookmaker’s implied probability for that outcome. The first step is to convert all odds — regardless of format — into implied probabilities.

Format	Formula	Example	Implied Prob
American +	100 / (odds + 100)	+150	40.0%
American −	\|odds\| / (\|odds\| + 100)	−130	56.5%
Decimal	1 / odds	2.50	40.0%
Fractional	denominator / (numerator + denominator)	3/2	40.0%

Step 2: Check for Arbitrage

Add the implied probabilities from the best available odds per outcome across different books. If the total is less than 100%, an arbitrage opportunity exists.

Example: Team A at +150 on DraftKings (40.0%) and Team B at +110 on FanDuel (47.6%). Total: 87.6% — that’s a 12.4% gap below 100%, meaning a guaranteed profit exists.

Step 3: Calculate Optimal Stakes

For equal profit across all outcomes, the stake on each outcome is proportional to its implied probability:

stake_i = total_stake × (implied_i / sum_of_all_implieds)

This ensures that no matter which outcome wins, you receive the same payout.

Step 4: Account for Fees

Platform fees reduce your actual payout. The calculator applies a flat fee percentage to all payouts. In practice, fees vary:

Polymarket: Variable taker fees by category (crypto 1.80%, sports 0.75%, politics/finance/tech 1.00%, others 1.25–1.56%; geopolitics fee-free)
Kalshi: Per-contract fee ($0.01/contract per side)
Sportsbooks: 4–10% vig built into odds (already reflected in the odds you enter)

Two-Way vs Three-Way Arbitrage

The calculator supports both two-outcome and three-outcome arbitrage.

Two-way arbs are the most common. Any event with two possible outcomes — Team A wins or Team B wins, YES or NO on a prediction market contract — can produce a two-way arb when different sportsbooks disagree on the probability. These are the easiest to find and execute because you only need to place two bets.

Three-way arbs arise in sports where draws are possible (soccer, hockey regulation time) or in markets with three discrete outcomes. The math is identical — sum the implied probabilities across all three outcomes from the best available odds at each book — but execution is harder. You need three separate bets at three different prices, and all three must be available simultaneously. Three-way arbs tend to be rarer but offer higher margins when they appear, because fewer automated scanners check three-way markets.

Cross-market arbs are a special case. When the same event is priced on both a sportsbook and a prediction market (e.g., Super Bowl winner on DraftKings and Polymarket), the different fee structures and market mechanics can create persistent pricing gaps. The Cross-Market Arbitrage Guide covers these in depth.

Common Arbitrage Pitfalls

Arb detection is the easy part. Execution is where most arb bettors lose money.

Stale odds. The odds you see on a comparison site or API may be seconds or minutes behind the sportsbook’s live price. By the time you place your bet, the line may have moved. Always verify the current price on the sportsbook itself before placing the second leg. If the first leg is already placed and the second-leg odds have moved, you may be stuck with an unhedged position.

Bet rejection and limits. Sportsbooks limit accounts that consistently take arb-favorable lines. Your $500 arb bet may be accepted at $50, destroying the position size you calculated. Accounts that show arb patterns — always taking the best line, betting both sides across books, unusual timing patterns — get flagged within weeks on most regulated US sportsbooks. Offshore books like Pinnacle and BookMaker are more tolerant.

Fee miscalculation. Prediction market fees vary by market type. Polymarket’s taker fee on general markets is roughly 2%, but crypto and sports markets can carry higher fees. Kalshi charges per-contract fees that change at different quantity thresholds. If your arb margin is 1.5% but your combined platform fees are 2%, you lose money on every trade.

Correlated outcomes. An arb only works when the two sides are genuinely independent markets. Betting “over 220.5 points” on one book and “under 221.5 points” on another is not an arb — there’s a gap where you lose both bets (221 points). Always confirm the lines are on the exact same market with no dead zone.

Settlement timing. Cross-platform arbs between sportsbooks and prediction markets have different settlement timelines. A sportsbook bet settles within hours of the game. A Polymarket contract might not resolve for days if the outcome requires verification. Your capital is locked for the longer duration, which affects effective ROI.

Where to Find Arbitrage Opportunities

Finding arbs manually — checking dozens of books for every event — is impractical. Here are the main approaches:

API-based scanning. The Odds API provides real-time odds from 10+ sportsbooks through a single endpoint. Pull odds for every event, calculate total implied probability per outcome pair, and flag anything below 100%. The Sports Betting Arbitrage Bot Guide walks through building this pipeline from scratch.

Cross-market tools. The Cross-Market Arb Finder compares sportsbook odds with prediction market prices on Polymarket and Kalshi, surfacing opportunities that single-platform scanners miss.

Opening line windows. The best arb windows appear when sportsbooks post opening lines at different times. If Bovada posts UFC odds 12 hours before DraftKings, the early line may contain value that disappears once the broader market adjusts. Monitoring opening-line timing across books is how professional arb operations find the highest-margin opportunities.

Line movement gaps. When a steam move hits sharp books (Pinnacle, Circa) but retail books (DraftKings, FanDuel) haven’t caught up, a temporary arb window opens. These last minutes, not hours — automated detection and fast execution are required.

What Is a Good Arb Percentage?

Arb %	Assessment
0.5–1.5%	Typical. Common in liquid sports markets. Thin margin — fees can erase it.
1.5–3.0%	Good. Worth pursuing if execution is fast.
3.0–5.0%	Strong. Usually appears around line movements or cross-market pricing.
5.0%+	Rare. Verify the odds are correct — may indicate a stale line or error.

Most sustainable arb operations target the 1–3% range and rely on volume for profit. The Sports Betting Arbitrage Bot Guide covers how to automate the full detection-to-execution pipeline.

Try It with Live Odds

This calculator works with any odds you type in, but finding real arbs manually means checking dozens of sportsbooks for every event. The Odds API delivers real-time odds from 10+ sportsbooks through a single API, making it easy to feed live data into your arb detection pipeline.