Published by ParlayAPI. This is a free tool we publish. The math runs entirely in your browser; nothing you type is sent anywhere. No signup, no email, no account required.

Arbitrage Calculator

Enter two prices on opposite outcomes at two different books. This tells you whether a guaranteed-profit arbitrage exists, the exact way to split your stake, and the profit you lock in. American or decimal odds, live as you type.

Your two prices

Outcome A at book 1, outcome B at book 2. They must be the opposite sides of the same two-way market.
Outcome A
decimal 1.9091
Outcome B
decimal 2.3000

Result

Updates as you type. All figures round for display only; the split uses full precision.
Arbitrage
--
Total implied probability --
Profit margin --
Stake on A --
Stake on B --
Return if A wins --
Return if B wins --
Guaranteed profit --

How it works

A two-outcome arbitrage exists when the two prices together imply a combined probability below 100 percent. The bookmakers, between them, are pricing the whole event at less than certainty, so a correctly split stake wins the same amount no matter which side hits. 

# 1. Convert each price to decimal odds
american +a  ->  dec = 1 + a/100
american -a  ->  dec = 1 + 100/a

# 2. Sum the implied probabilities
total_implied = (1 / dec_a) + (1 / dec_b)

# 3. Arb exists only if total_implied < 1
profit_margin = (1 / total_implied) - 1        # e.g. 0.05 = 5%

# 4. Split a total stake S so both outcomes return the same
stake_a = S * (1 / dec_a) / total_implied
stake_b = S * (1 / dec_b) / total_implied
each_outcome_returns = S / total_implied
guaranteed_profit    = S / total_implied - S
  1. If total_implied is 1 or greater, there is no arb. The calculator says so and shows how far underwater the pair is.
  2. The stake split makes stake_a * dec_a equal to stake_b * dec_b, so your payout is identical either way.
  3. Profit is the same dollars whichever side wins, which is what makes it "guaranteed" on paper.

Read this before you bet on it

"Guaranteed" is a math statement, not a promise about the real world. Books limit, restrict, or close accounts that arb, and they can void a bet on a palpable error or a market it should not have offered.

Prices move. The line you saw a moment ago may be gone before your second bet is placed, which can leave you with only one side and real exposure. Sizing limits, minimum bets, rounding, and any bet that fails to place all eat into or erase the margin this page computes.

Treat the output as the theoretical ceiling for an idealized, instantaneous, unrestricted pair of bets, and nothing more.

This is the same devig and edge math ParlayAPI runs at scale. The /v1/ev and /v1/devig endpoints run this class of no-vig and edge computation across 45+ sources so you do not have to paste prices by hand. See the docs or pricing.