Arbs › Calculators › EV calculator

Expected value betting calculator

Expected value is what a bet earns on average if you could make it many times. Enter a price and a win chance or a fair line.

EV calculator illustration

The formula

EV = p × d − 1; break-even p = 1 ÷ d

p is the win probability and d the decimal odds. EV is per unit staked.

A positive number is a +EV bet; a negative one loses money over time even if it wins tonight. At +100 you need to win more than 50%; at −150 more than 60%.

Where the win probability comes from

The hard part is the probability, not the arithmetic. Two common sources are a sharp book’s no-vig line and a model. Arbs shows its model probability next to every Polymarket price on the board, and publishes how those numbers did on the track record.

Worked example

Worked example: +100 with a 55% win chance

  1. Decimal odds: 2.00, so break-even is 50%
  2. EV: 0.55 × 2.00 − 1 = 0.10

+10%, or +$10 per $100 staked on average.

Frequently asked questions

What is a +EV bet?

A bet whose price pays more than its true chance of winning is worth. Over many bets, +EV bets make money on average; any single one can still lose.

How do I calculate expected value in betting?

Multiply your win probability by the decimal odds and subtract 1. 0.55 × 2.00 − 1 = 0.10, so +10% of the stake.

What EV is worth betting?

Anything positive is +EV in theory, but estimates are noisy. Many bettors wait for 2–3% or more so a small error in the probability does not flip the sign.

Read the guide: Expected value betting, with worked examples

See today’s model gaps on the live board · How Arbs prices games

More free calculators

Free betting calculators · Guides · Glossary · How Arbs works · Odds by league · Track record · Responsible gaming