How do you convert American odds to decimal odds?

For positive American odds, divide by 100 and add 1 (e.g. +150 = 150/100 + 1 = 2.50). For negative American odds, divide 100 by the absolute value and add 1 (e.g. -200 = 100/200 + 1 = 1.50).

What is implied probability?

Implied probability is the break-even win rate baked into a price. It equals 1 divided by the decimal odds. Decimal 2.00 implies 50%, 1.50 implies 66.7%.

What does removing the vig (no-vig) mean?

Sportsbooks pad both sides of a market so the implied probabilities add up to more than 100%. Removing the vig rescales both sides back to 100% to reveal the book's true, fair estimate of each outcome.

How do you calculate expected value (EV) on a bet?

EV% = (true win probability x decimal odds - 1) x 100. If your true probability of winning is higher than the price implies, EV is positive and the bet is +EV over the long run.

The Free Odds Calculator

Convert any odds format, find the implied probability, strip out the vig for a fair line, and check the expected value before you bet. No signup, no cost.

American · Decimal · Fractional No-Vig / De-Vig Expected Value Parlay & Hold

Odds Converter No-Vig / Fair Odds Expected Value Parlay Payout Book Hold

Odds Converter

Type a value in any field — the rest update instantly. American ↔ Decimal ↔ Fractional ↔ Implied probability.

American

Decimal

Fractional

Implied Probability (%)

Implied probability is the break-even win rate a price is charging you. Beat that number consistently and you profit.

No-Vig Fair Odds

Enter both sides of a two-way market (e.g. Over/Under, or two moneylines). We remove the sportsbook's built-in margin and show the fair, no-vig price and probability for each side.

Side A odds (American)

Side B odds (American)

Why it matters: the no-vig price is the closest thing to the market's honest opinion. If a different book (or the other side) offers a better number than the fair odds, that's where the value is.

Expected Value (EV)

Compare the price you're getting to what you believe the true win probability is. Positive EV means the bet pays more than it should over the long run.

Your odds (American)

True win probability (%)

Stake ($)

Tip: for the "true probability," the sharpest free estimate is the no-vig fair probability from a sharp book like Pinnacle or a low-hold exchange. That's exactly how Odds Piranha flags +EV bets automatically.

Parlay Calculator

Add each leg's American odds to see the combined price and payout. Note: this is the fair independent-legs price — sportsbooks shorten same-game parlays for correlation.

Stake ($)

Book Hold / Vig

Enter both sides of a market to see how much the sportsbook is holding — the built-in margin you're paying. Lower hold = better price for you.

Side A odds (American)

Side B odds (American)

How betting odds actually work

American, decimal, and fractional — same price, three languages

Every odds format describes the same thing: how much you win and how likely the book thinks it is. American odds show what you'd win on $100 (or what you'd risk to win $100 for favorites). Decimal odds show your total return per $1 staked. Fractional odds show profit relative to stake. Use the converter above to move between them instantly.

American	Decimal	Fractional	Implied %
-200	1.50	1/2	66.7%
-110	1.91	10/11	52.4%
+100	2.00	1/1	50.0%
+150	2.50	3/2	40.0%
+300	4.00	3/1	25.0%

Implied probability: the number that matters most

Implied probability = 1 ÷ decimal odds. It's the win rate you'd need just to break even at that price. If a bet is priced at -110 (52.4% implied) but you believe it hits 55% of the time, you have an edge. Almost all sharp betting comes down to this one comparison: your estimate vs. the price's implied probability.

Removing the vig — finding the fair line

Sportsbooks quote both sides so the implied probabilities add up to more than 100% — that overround is their margin. A standard -110/-110 market implies 52.4% + 52.4% = 104.8%, so the book holds about 4.5%. To find the fair price, rescale both sides back to 100%. The no-vig line is the market's honest estimate, and it's the benchmark you compare every other book's price against.

Expected value: is the bet actually worth it?

EV% = (true probability × decimal odds − 1) × 100. Positive EV means that, priced against your true probability, the bet pays more than it costs over the long run. You won't win every +EV bet — variance is real — but stacking positive-EV bets is the entire mathematical basis of profitable betting. The hard part is getting an honest "true probability," which is why the no-vig line from a sharp book is such a useful free proxy.

Don't do this math by hand every night.

Odds Piranha runs all of it automatically across every book — de-vigs the sharp line, flags the +EV bets, and points you to the best number two taps before the line moves.

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