Kelly Criterion American Odds Calculator

Calculator

Bankroll

American Odds

Estimated Win Probability (%)

Kelly Fraction

Minimum Stake

Rounding Step

Maximum Stake Cap (%)

Money Symbol

Formula Used

The calculator first converts American odds into decimal odds.

For positive odds: Decimal Odds = 1 + American Odds / 100.

For negative odds: Decimal Odds = 1 + 100 / Absolute American Odds.

Net odds are decimal odds minus one.

Full Kelly fraction = (b × p - q) / b.

Here, b is net odds, p is win probability, and q is loss probability.

Selected stake = Bankroll × Full Kelly × Kelly Fraction.

How to Use This Calculator

Enter your total bankroll.
Enter American odds, such as +150 or -120.
Add your estimated chance of winning.
Choose a Kelly fraction for risk control.
Add minimum stake, rounding, and cap settings.
Press Calculate to view the suggested stake.
Use CSV or PDF export to save the result.

Example Data Table

Bankroll	American Odds	Win Chance	Kelly Fraction	Full Kelly	Suggested Stake
$1,000	+150	45%	0.50	8.33%	$41.67
$1,000	-120	55%	0.50	1.00%	$5.00
$1,000	+200	32%	0.50	No edge	$0.00

Kelly Criterion American Odds Guide

Why Bankroll Sizing Matters

The Kelly Criterion helps size a stake from perceived value. It compares your estimated win chance with market odds. The goal is not to predict every result. The goal is to avoid oversized bets when value is small.

How American Odds Are Converted

American odds need conversion before the formula works. Positive odds show profit on a 100 unit stake. Negative odds show the stake needed to win 100 units. The calculator converts both formats into net profit per unit risked.

Why Fractional Kelly Helps

A full Kelly stake can grow a bankroll fast. It can also feel aggressive during losing runs. Many users choose half Kelly, quarter Kelly, or another fraction. Fractional use lowers volatility while keeping the logic intact.

Probability Is the Key Input

The most important input is your true win probability. This number should come from research, pricing, or a model. Guessing too high can create false value. A small mistake can change a suggested stake from safe to risky.

Understanding Edge

The calculator also shows implied probability. This is the break even chance set by the listed odds. If your win chance is higher, the wager may have positive edge. If your chance is lower, the tool suggests no stake.

Using the Bankroll Field

Bankroll size controls the money amount. The Kelly percentage controls the portion. A larger bankroll does not improve the bet. It only changes the stake size connected to the same percentage.

Advanced Controls

Use the advanced fields to set a minimum stake and rounding step. These options help match practical betting limits. They also make the final amount easier to place. The CSV and document exports record the inputs and results.

Responsible Use

This calculator is a planning tool. It cannot remove uncertainty. It should not replace discipline, limits, or responsible choices. Use conservative probabilities. Track results over time. Stop when assumptions prove weak. A good process matters more than one outcome.

Reviewing Results

For best results, separate price opinion from emotion. Write the reason for your probability estimate. Then compare it against the edge shown. If the value is tiny, passing may be better. If the value is clear, the fraction setting can scale exposure. Repeat the same method for every market. Consistency makes records easier to review and improves future estimates. Keep records simple, honest, and linked to each original probability estimate before review later.

FAQs

What is the Kelly Criterion?

It is a staking formula. It compares your estimated win probability with the price offered. The result suggests what share of bankroll to risk when the wager has value.

Does this calculator work with negative American odds?

Yes. Enter odds like -110 or -150. The calculator converts them into decimal odds, net odds, implied probability, edge, and suggested stake.

What does Kelly fraction mean?

It reduces the full Kelly stake. A value of 1 uses full Kelly. A value of 0.50 uses half Kelly. Smaller values reduce volatility.

Why does the result show zero stake?

A zero stake appears when your estimated probability does not beat the odds. It can also appear when the suggested stake is below your minimum setting.

What is implied probability?

Implied probability is the break even chance from the listed odds. Your estimated chance must be higher than this value before Kelly suggests a positive stake.

Should I always use full Kelly?

No. Full Kelly can be aggressive. Many users prefer half Kelly or quarter Kelly. This helps manage drawdowns and emotional pressure.

What does expected value per unit mean?

It estimates the average profit or loss for one unit staked. Positive value means your probability estimate is higher than the market break even chance.

Can this guarantee profit?

No. It only sizes stakes from your assumptions. Poor probability estimates can create poor results. Use careful research and responsible bankroll limits.