Bet Calculator
Betting Odds Calculator works out Decimal odds and American / moneyline odds from What to calculate, Odds and Odds format. The default figures on this page give decimal odds of 2.5; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
2 steps
- Decimal price = 2.5, i.e. 150 American, 3/2 fractional, 40% implied.
- A stake of 100 returns 250 in total, a profit of 150.
Its 5 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
4 sources
What the Betting Odds Calculator calculates
Converts between American, decimal, fractional and implied-probability odds, works out payouts and parlay returns, strips the bookmaker margin to give no-vig fair prices, finds arbitrage stakes across books, sizes a bet by the Kelly criterion and computes hedge stakes and martingale sequences.
How to use this Betting Odds Calculator
Enter What to calculate, Odds, Odds format and Stake. Decimal odds updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Decimal odds, American / moneyline odds and Fractional odds.
The method follows Kelly, J.L. Jr (1956), "A New Interpretation of Information Rate", Bell System Technical Journal 35(4), 917-926, Thorp, E.O. (2006), "The Kelly Criterion in Blackjack, Sports Betting and the Stock Market", Handbook of Asset and Liability Management, Elsevier, Cortis, D. (2015), "Expected values and variances in bookmaker payouts: a theoretical approach towards setting limits on odds", Journal of Prediction Markets 9(1), 1-14 and Shin, H.S. (1993), "Measuring the incidence of insider trading in a market for state-contingent claims", The Economic Journal 103(420), 1141-1153.
Convert +150 American odds example
With What to calculate: convert, Odds: +150, Stake: 100, the calculator returns Decimal odds: 2.5, American / moneyline odds: 150, Fractional odds: 3/2. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Decimal odds, American / moneyline odds and Fractional odds. The inputs you can vary are What to calculate, Odds, Odds format, Stake, Odds for each leg or outcome and Your estimated win probability.
Understanding Decimal odds, American / moneyline odds and Fractional odds
This is an arithmetic tool, not betting advice. Bookmaker prices already carry a margin, so the long-run expected value of a bet at posted odds is negative unless you genuinely have an edge. Gamble only what you can afford to lose.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How to calculate odds for a bet?
Converts between American, decimal, fractional and implied-probability odds, works out payouts and parlay returns, strips the bookmaker margin to give no-vig fair prices, finds arbitrage stakes across books. Open “How this is worked out” beside the result to see each step for your own figures.
What is +200 odds as a percentage?
Converts between American, decimal, fractional and implied-probability odds, works out payouts and parlay returns, strips the bookmaker margin to give no-vig fair prices, finds arbitrage stakes across books. On this page it is computed from What to calculate, Odds and Odds format and shown as Decimal odds, American / moneyline odds and Fractional odds.
How do I work out my odds?
It needs What to calculate, Odds, Odds format, Stake, Odds for each leg or outcome and Your estimated win probability. Nothing else is required, and the figures stay in your browser.
How much would you win if you bet $100 on odds?
On the figures this page opens with — stake 100 — the decimal odds is 2.5. No single number fits everyone: change any figure above and the answer updates as you type, with each step of the arithmetic beside it.
Is there a free bet calculator app available?
The calculation is free and does not require an account. An account is only needed for optional features such as saving, comparing, exporting, or sharing supported scenarios.
What information do I need for the Betting Odds Calculator?
You need What to calculate, Odds, Odds format, Stake, Odds for each leg or outcome, Your estimated win probability, Bankroll and Kelly fraction. The page opens with default figures that give decimal odds of 2.5, so you can see the scale before entering your own.