Convert American, decimal, and fractional betting odds, then check implied probability, payout, expected value, edge, and Kelly stake sizing.
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Odds converter
Convert odds, check break-even rate, and test your edge.
Enter American, decimal, or fractional odds to see the implied probability, payout, expected value, and Kelly-sized stake from your own probability estimate.
Odds format
Assumptions
Implied probability is the break-even rate before removing sportsbook vig. EV and Kelly outputs depend entirely on your probability estimate, so treat them as a sensitivity check rather than betting advice.
Positive EV by your estimate
52.38% break-even
Your estimate is 2.62 percentage points above the break-even rate, so the line is positive EV if that probability is realistic.
Fractional
10/11
Decimal
1.91
American
-110
Implied probability
52.38%
Potential profit
90.91
Total payout
190.91
Your probability
55%
Edge vs break-even
+2.62 pts
Expected profit
+5
Expected ROI
+5%
Fair odds from your estimate
A 55% true probability corresponds to about 1.82 decimal, -122, or 9/11 before vig. Better offered odds than that are favorable only if your estimate is well calibrated.
Kelly stake check
Full Kelly suggests 5.5% of bankroll; half Kelly suggests 27.5 on the bankroll entered. A zero stake means the edge is not positive under your estimate.
Market note
For a two-sided market, add both sides’ implied probabilities to estimate the overround. For example, -110 on each side totals about 104.76%, so each side’s raw 52.38% break-even rate includes roughly 4.76 percentage points of sportsbook margin.
Convert odds formats and calculate implied probability
An odds calculator converts between fractional, decimal, and moneyline (American) odds formats, and calculates the implied probability, break-even win rate, potential payout, expected value, and Kelly stake for any stake. Use it as an odds converter and implied probability calculator when you want to compare prices across sportsbooks, understand a moneyline, or test whether your own probability estimate is high enough to justify the risk.
How odds formats relate to each other
Fractional odds like 5/1 mean you win five units for every one unit staked (plus your stake back). The same probability expressed as decimal odds is 6.00, and as American odds is +500. All three express the same payout ratio in different conventions.
Decimal odds are the simplest: multiply your stake by the decimal to get the total return including stake. Fractional odds are traditional in the UK and Ireland. American odds are standard in the US, with positive numbers showing profit on a 100-unit stake and negative numbers showing how much you must stake to win 100.
Implied probability and overround
Implied probability is the break-even win rate implied by the odds. For decimal odds, it is 1 divided by the decimal. For 2.00 odds, the implied probability is 50 percent. Bookmakers set odds so that the total implied probability across all outcomes exceeds 100 percent — the excess is the overround or margin, which is how they profit.
Implied Probability = 1 / Decimal Odds
Multiply by 100 to express as a percentage.
Why expected value belongs in a betting odds calculator
A conversion alone tells you what the market price means. It does not tell you whether the price is attractive. That is why this page lets you enter your own true probability estimate and compares it with the implied probability. If your estimate is higher than the break-even win rate, the line has positive expected value under your assumptions; if it is lower, the payout is not enough for the risk.
For example, a -110 line implies about 52.38 percent. If you estimate the outcome at 55 percent and stake 100, the expected profit is positive because your win probability clears the required break-even rate. If your estimate is only 50 percent, the same -110 line is negative expected value before taxes, limits, or bankroll constraints.
EV = p × Profit if Win − (1 − p) × Stake
Expected value uses your probability estimate, not the sportsbook's implied probability.
Edge = Your Probability − Implied Probability
A positive edge means your estimate is above the break-even rate implied by the odds.
Reading American, decimal, and fractional odds side by side
American odds are common in the United States and are often called moneyline odds. Positive American odds show profit on a 100-unit stake, so +200 means 100 can win 200 in profit. Negative American odds show how much must be risked to win 100, so -200 means 200 must be staked to win 100.
Decimal odds are often the easiest format for payout math because total return is simply stake multiplied by decimal odds. Fractional odds show profit relative to stake, which is why 7/2 means a 2-unit stake can win 7 units of profit. The calculator keeps all three formats visible so you can line-shop without doing the conversion manually.
Kelly staking is a sensitivity check, not a command
The Kelly criterion converts edge and payout into a suggested bankroll fraction. It can be useful because it shows how quickly a suggested stake collapses to zero when the edge disappears. But Kelly staking is highly sensitive to probability error, and full Kelly can be volatile even when the estimate is sound.
This page shows full Kelly and half Kelly from the bankroll you enter, while keeping the responsible interpretation front and center: if your probability estimate is weak, untested, or based on a small sample, the sizing output can be more confident than the evidence deserves.
Vig, no-vig probability, and why implied probability is not always fair probability
Sportsbook odds usually include vig, also called juice or margin. In a two-sided market with -110 on both sides, each side has about 52.38 percent implied probability, so the two sides total about 104.76 percent. The extra 4.76 percentage points are the overround.
That is why implied probability is best read as a break-even rate, not a pure forecast. To estimate no-vig probability across a full market, convert each outcome to implied probability, add them together, and divide each outcome by the total so the set normalizes back to 100 percent.
No-vig Probability = Outcome Implied Probability / Total Market Implied Probability
Use this only when you have all mutually exclusive outcomes for the same market.
Frequently asked questions
What does "even money" mean?
Even money means the payout equals your stake: you risk one unit to win one unit. In fractional odds it is 1/1 (evens), in decimal it is 2.00, and in American it is +100. The implied probability is 50 percent before the bookmaker margin.
How do I spot a value bet?
A value bet exists when you believe the true probability of an outcome is higher than the implied probability of the odds offered. If you estimate a team has a 60 percent chance of winning but the odds imply only 50 percent, the bet has positive expected value.
What is the difference between an odds converter and an implied probability calculator?
An odds converter translates the same price between American, decimal, and fractional odds. An implied probability calculator converts that price into the break-even win rate. This page does both, then adds payout, expected value, and Kelly stake checks from your own probability estimate.
How do you convert American odds to probability?
For positive American odds, divide 100 by the odds plus 100. For +200, the implied probability is 100 / 300 = 33.33 percent. For negative American odds, divide the absolute value by the absolute value plus 100. For -150, the implied probability is 150 / 250 = 60 percent.
Why does -110 need more than 50 percent to break even?
-110 means you risk 110 to win 100, so the payout is slightly worse than even money. The break-even win rate is 110 / 210 = 52.38 percent. A bettor who wins exactly half of -110 wagers loses money over time because the sportsbook's vig is built into the price.
How does this odds payout calculator handle stake?
Stake is optional. When you enter it, the calculator shows potential profit and total payout. Potential profit is the amount won beyond the original stake, while total payout includes the returned stake plus profit.
What does positive EV mean in betting odds?
Positive EV means the probability you assign to the outcome is high enough that the average expected profit is above zero at the offered odds. It does not mean the individual wager will win, and it depends completely on whether your probability estimate is accurate.
Should I follow the Kelly stake exactly?
No. Kelly staking is a mathematical benchmark, not a responsible gambling instruction. It is very sensitive to probability error, and full Kelly can create large swings. Many disciplined bettors use smaller fractions or skip staking entirely when the probability estimate is uncertain.
Does implied probability remove the vig?
No. Raw implied probability includes sportsbook margin. To estimate no-vig probability, you need all outcomes in the same market, convert each to implied probability, total them, and divide each outcome by that total.
