How cross-market arbitrage works

The one-sentence idea

If you can buy every outcome of an event — spread across different platforms — for a combined cost of less than $1.00, you lock in a profit no matter who wins.

Every price is shown one way across the whole dashboard: what it costs to win $1. A price of $0.62 means you pay 62 cents to win a dollar — which is also the market saying there's a 62% chance. Sportsbook odds are converted to the same unit, so Kalshi, Polymarket, FanDuel and DraftKings are directly comparable. Add up the cheapest price for each outcome; if the total is under $1.00, the gap is your guaranteed margin.

A worked example

Say the Lakers play the Celtics. Here's the cheapest price for each side, per venue:

You spent $0.95 to guarantee a $1.00 payout — a +5.3% risk-free return. Split a $100 bankroll ~$42 on Lakers @ Kalshi and ~$58 on Celtics @ Polymarket, and either result pays back ~$105. That split is the “stake playbook” the dashboard prints for every arb.

Why these gaps exist

The same event is priced by different crowds. Prediction markets (Kalshi, Polymarket) are moved by traders; sportsbooks (FanDuel, DraftKings) shade lines for betting volume and their own margin. They don't always agree — and when they don't, the cheapest side of each outcome can live on different platforms. Arb Radar's job is to line up the same event across all of them and do the arithmetic instantly.

Arbitrage vs. +EV value bets

A true arbitrage is rare — markets are efficient, and a guaranteed edge vanishes fast. So Arb Radar also finds +EV (positive expected value) bets, which show up far more often.

How we judge "fair": every venue's posted prices include a built-in margin (vig). We strip that out and take the prediction markets (Kalshi & Polymarket) as the sharp reference — they're moved by real money and tend to be efficient. When a sportsbook offers better odds than that fair line, the gap is your +EV%. Betting those consistently is how sharp bettors grind out profit without needing a perfect arb.

Example: if the prediction-market fair line puts the Lakers at $0.50, but FanDuel is selling the same outcome for $0.43, you're paying 7 cents less than it's worth — roughly +16% EV.

Reading the dashboard

• Source pills — every venue currently being scanned, with how many markets each is contributing. Green means live data is flowing.
• Event cards — one per matched event. The big number is the guaranteed margin: green is a real arb, amber means no edge right now.
• Open a card — see every venue's price per outcome, with the cheapest marked “best”, plus the risk-free stake split.
• Plus EV badge — a value bet: the venue, side, and estimated edge vs the prediction-market fair line, shown even when there's no guaranteed arb.
• Pick your venues — click any source pill to exclude a venue you don't have an account with. Everything is recalculated, not just hidden: if your excluded venue was supplying the cheapest leg, the margin drops to what you can actually get, and the opportunity disappears entirely if it no longer clears $1.00. Your choice is remembered.
• Venue names are links — each one opens that exact market on the venue, with the selection already chosen where the site supports it. Use ⚡ Open all legs to open every side of an arb at once. An arb only pays if both legs get filled, so the fewer clicks between spotting and placing, the more of the edge survives.
• Auto-refresh + alerts — prices refresh every 15 seconds on their own. Raise the minimum-margin slider to hide small edges, and toggle the bell for sound and desktop alerts the instant a new arb appears.