Kelly Criterion Calculator for Sports Betting
Turn bankroll, sportsbook odds, and your estimated win probability into a disciplined bet size. See Full Kelly, Half Kelly, Quarter Kelly, expected value, edge, and risk level in one readout.
Free Kelly Criterion Calculator
Enter your bankroll, American odds, and true win probability estimate. The tool calculates bet size and tells you when the math says to pass.
Use the dedicated bankroll you can actually risk.
Enter a bankroll greater than zero.
Use the exact price available at the book.
Enter valid American odds outside the -100 to +100 range.
This is your true probability estimate, not the sportsbook's implied probability.
Enter a probability between 0.1% and 99.9%.
Half Kelly is the practical default for most bettors.
The Kelly Criterion answers the question most bettors skip: how much?
Finding a positive expected value bet is only step one. The second decision is position size. Bet too little and the edge barely matters. Bet too much and normal variance can wreck the bankroll even when the bet is good. Kelly turns the odds and your probability estimate into a stake size designed for long-run growth.
The market asks you to win 52.38% to break even.
Your probability estimate is 4.62 percentage points above breakeven.
On $1,000, the disciplined stake is $48.50.
Kelly Criterion formula for sports betting
The formula uses net odds and probability. Net odds are the profit you receive for every $1 staked. At -110, you profit about $0.91 for each $1 risked. At +150, you profit $1.50 for each $1 risked.
f = bankroll fraction, b = net odds, p = win probability, q = loss probability
Convert the odds
Turn American odds into net odds. -110 becomes 0.909. +150 becomes 1.50.
Estimate probability
Use your own researched probability, not the sportsbook's implied probability.
Apply a fraction
Use Full Kelly only when inputs are extremely reliable. Most bettors should use Half or Quarter Kelly.
Full Kelly vs Half Kelly vs Quarter Kelly
The calculator shows all three because the mathematically optimal answer is not always the most practical answer. Model error matters. If your probability estimate is too high, Full Kelly will overbet.
| Fraction | What it does | Risk | Best use |
|---|---|---|---|
| Full Kelly | Uses 100% of the formula output | High | Validated models with strong calibration |
| Half Kelly | Uses 50% of the formula output | Medium | Best default for serious sports bettors |
| Quarter Kelly | Uses 25% of the formula output | Lower | New bettors, uncertain markets, volatile props |
| Zero Kelly | Bet is not positive EV | Best risk | Skip and protect the bankroll |
Quarter Kelly calculator examples for noisy sports markets
Quarter Kelly is often the safer search-intent answer for sports bettors because the probability input is usually the weakest part of the workflow. Injury news, lineup changes, limits, and stale odds can make a clean model estimate too confident.
$500 bankroll, -150, 63%
Full Kelly is small because the price is expensive. Quarter Kelly keeps the position modest while still rewarding a positive edge.
$2,500 bankroll, +150, 44%
Plus odds can produce larger Kelly outputs. Quarter Kelly helps prevent one attractive underdog from becoming too much of the bankroll.
$1,000 bankroll, -110, 51%
The calculator should say to skip it. A smaller Kelly fraction does not turn a negative EV bet into a good bet.
If you are using Kelly after a slip screenshot review, first verify the line and probability with the AI bet slip analyzer workflow, then size only the bets that still clear the expected value check.
Why negative Kelly means skip the bet
Kelly becomes negative when your estimated win probability is below the breakeven probability required by the odds. That is not a calculator error. It is the whole point of the tool. A negative output means the price is not good enough for your estimate.
52.38% breakeven
Below the price required
No stake size fixes a negative EV bet
Before sizing a bet, use the EV Calculator to confirm the bet is positive expected value. If your odds are not in American format, start with the Betting Odds Converter.
Kelly Criterion mistakes that wreck bankrolls
Using confidence as probability
Feeling strong about a side is not the same as having a 60% true probability. Kelly punishes inflated inputs.
Ignoring correlation
Multiple bets on the same game can move together. Standard Kelly assumes independent positions.
Using Full Kelly by default
Full Kelly is fragile when estimates are noisy. Half Kelly is usually the better practical choice.
Chasing after losses
Kelly sizes off current bankroll. Losses reduce stake size. That automatic downshift is a feature.
Where Juice fits in the workflow
This calculator does not estimate probability for you. It sizes a bet after you bring a probability estimate. For probability and EV context, Juice analyzes bet screenshots, compares odds across sportsbooks, and gives a research-driven probability readout. Bring that probability here if you want to translate an edge into a stake size.
To compare the broader category, read our roundup of the best sports betting research apps, including tools for AI bet analysis, +EV screens, player props, and bet tracking.
Kelly Criterion calculator FAQ
What is a good Kelly percentage for sports betting?
Most realistic sports-betting edges create modest Kelly percentages. After applying Half Kelly, many disciplined stakes land under 5% of bankroll. Larger outputs should make you inspect the probability estimate carefully.
What is a quarter Kelly calculator?
A quarter Kelly calculator applies 25% of the full Kelly output. It is useful when your probability estimate is directionally helpful but not precise enough to justify Full Kelly sizing.
How does a Kelly betting calculator handle negative EV bets?
It should recommend no bet. If your estimated probability is lower than the breakeven probability implied by the odds, Kelly turns negative and the right move is to pass.
Should beginners use Kelly Criterion?
Beginners can use Kelly as a discipline check, but Quarter Kelly is safer than Full Kelly while learning. The hardest input is probability estimation, not the formula.
Can Kelly Criterion be used for parlays?
Yes, but calculate the parlay as one combined bet. Use the full parlay price and the combined win probability. Do not calculate Kelly on each leg separately.
How often should I recalculate Kelly?
Recalculate before each bet using your current bankroll, current odds, and current probability estimate. Kelly automatically scales down after losses and up after wins.
What happens if Kelly says to bet more than I am comfortable with?
Use a smaller fraction, such as Quarter Kelly, or pass. Kelly is not a command to ignore comfort, liquidity, limits, or model uncertainty.