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Odds Calculator
Convert decimal, fractional, and American odds. Calculate returns, accumulators, each-way bets, and Kelly Criterion stake sizing. No sign-up, no tracking.
Enter a price in any format. The others update automatically.
How it worksDecimal odds give total return per unit staked (2.00 returns £2 on £1 including stake). Fractional shows profit-to-stake (5/1 = £5 profit on £1). American: stake required to win 100 (negative) or win on a 100 stake (positive). Implied probability is the break-even rate before margin.
Calculate the return on a single bet. Works with any odds format.
Build an accumulator. Returns multiply — every leg must win.
Reality checkEvery leg multiplies the bookmaker’s margin against you. A four-leg accumulator at 105% per market compounds to a 121% effective overround. Treat them as entertainment, not as +EV bets.
Calculate each-way bets — half stake to win, half to place.
The Kelly Criterion calculates optimal stake size based on edge and bankroll.
About KellyFull Kelly maximises growth in theory but produces large drawdowns. Most professionals use Half Kelly or less as a buffer against estimation error. A negative result means the market offers worse odds than your estimate — correct stake is zero.