Odds Calculator
Convert between probability, decimal odds, fractional odds, and American odds. Add an optional stake to estimate profit and total return.
- Implied probability from decimal odds:
p = 1 / decimal - Decimal from American (+A):
1 + (A / 100); from American (-A):1 + (100 / A) - Profit from stake:
stake × (decimal - 1)
Why use a calculator for odds?
Odds are just another way of expressing probability and potential payout. The challenge is that people encounter different formats in different places: sportsbooks often use American odds, many international markets use decimal odds, and traditional UK-style markets use fractional odds. A calculator removes conversion mistakes and helps you compare options on a single, consistent basis.
In practical terms, odds conversion is useful for sports betting analysis, risk modeling, pricing decisions, and any scenario where you need to answer: “What chance is this number implying?” and “What would I win if I risked X?”
Understanding the four core formats
1) Probability (%)
Probability is the most intuitive format. If an event has a 40% probability, it is expected to happen 40 times out of 100 over the long run. Odds formats can always be converted back into this percentage, which is why implied probability is a key comparison metric.
2) Decimal odds
Decimal odds show total return per 1 unit staked (including your original stake). Example: decimal odds of 2.50 mean every $1 stake returns $2.50 total, so profit is $1.50.
3) Fractional odds
Fractional odds show net profit relative to stake. Example: 5/2 means profit of $5 for every $2 staked (plus you get your $2 stake back).
4) American odds
American odds use positive and negative numbers:
- Positive odds (e.g., +220): profit on a $100 stake.
- Negative odds (e.g., -150): stake needed to profit $100.
How to use this odds calculator
- Select the conversion type.
- Enter your value in the relevant field.
- Optionally enter a stake to estimate return and profit.
- Click Calculate to see all converted formats together.
This workflow is especially useful when comparing two lines in different formats. Convert both to implied probability first, then compare to your own estimate of the true probability.
Worked examples
Example A: Probability to odds
Suppose you estimate a team has a 42% chance to win. The equivalent decimal odds are approximately 2.38. This corresponds to fractional odds near 29/21 and American odds around +138.
Example B: American odds to probability
A line of -150 implies a probability of about 60%. If your own model says the event wins only 54% of the time, that line is likely overpriced.
Example C: Stake impact
At decimal odds 3.20, a $50 stake returns $160 total:
- Profit: $110
- Returned stake: $50
- Total return: $160
From conversion to decision-making
Converting odds is step one. Step two is assessing whether a price is favorable. A common framework is expected value (EV):
EV = (your probability × profit if win) − ((1 − your probability) × stake)
If EV is positive over many similar decisions, the strategy may be favorable in the long run. If EV is negative, even occasional wins can hide an unfavorable underlying price.
Common mistakes to avoid
- Confusing total return with net profit.
- Comparing lines in different formats without conversion.
- Ignoring implied probability and focusing only on payout size.
- Forgetting that short-term outcomes can differ from long-term expectation.
Final thoughts
A reliable calculator for odds helps you translate numbers quickly, reduce errors, and make better comparisons. Whether you are analyzing markets, evaluating risk, or learning probability, odds conversion gives you a clearer view of what each number actually means.