Published May 29, 2026
Bankroll Management and the Kelly Criterion for Sports Bettors
An edge means nothing if you go broke before it pays off. Bankroll management is the part of betting that decides whether a real edge survives a bad week, and it is the half of the process most bettors skip.
Finding good prices is one skill. Sizing your bets so variance does not wipe you out is a separate one. You can be right about +EV on every bet and still bust if you stake too much per play. This guide covers how to set a bankroll, the common staking methods, and how the Kelly criterion turns your edge into a bet size.
What a bankroll actually is
Your bankroll is the money set aside only for betting. It is not your rent, not your savings, and not a number you top up mid-session because you are down. Once you mix betting money with money you need, you stop making sizing decisions on math and start making them on emotion.
A few rules that keep a bankroll honest:
- Keep it separate. A dedicated account or a fixed number you track makes every other decision easier.
- Define a unit. Most bettors set one unit at 1% to 2% of the bankroll. A $5,000 bankroll at 1% means a unit of $50.
- Do not reload to chase. If the bankroll is gone, the session is over. Adding money to recover a loss is how a sizing plan turns into gambling.
Flat staking vs unit staking vs percentage staking
There are three common ways to decide how much to bet.
Flat staking
You bet the same dollar amount every time, say $50. Simple, low variance, easy to track. The downside is it ignores both the size of your edge and the growth of your bankroll. A small +EV spot and a large one get the same stake.
Unit staking
You bet in units (1 unit, 2 units) based on how confident you are. This is better than flat betting if your confidence is well calibrated, and worse if it is not. Most bettors are not as good at ranking their own edges as they think.
Percentage staking
You bet a fixed percentage of your current bankroll. Stakes grow when you win and shrink when you lose, which protects you during downswings and compounds during upswings. This is the family that the Kelly criterion belongs to.
The Kelly criterion in plain terms
Kelly answers one question: given your edge and the price, what fraction of your bankroll maximizes long-run growth?
The rule in one sentence: bet more when your edge is larger and the payout is bigger, and bet less when the edge is thin or the price is short.
For a simple bet, the Kelly fraction is:
f = (bp - q) / b
bis the decimal payout minus 1 (the profit per $1 staked)pis your estimated true win probabilityqis1 - p
You only ever need this if you are computing stakes by hand. The +EV feed already surfaces a suggested Kelly stake for each bet, but it helps to understand where the number comes from.
A worked example
Take a moneyline priced at +120. That is a decimal price of 2.20, so b = 1.20. Suppose your consensus estimate of the true win probability is 50%, so p = 0.50 and q = 0.50.
f = (1.20 * 0.50 - 0.50) / 1.20 = (0.60 - 0.50) / 1.20 = 0.083
Full Kelly says stake about 8.3% of your bankroll on this bet. On a $5,000 bankroll that is roughly $415. That is a large swing for a bet you expect to lose half the time, which is exactly why most bettors do not use full Kelly.
Why serious bettors use fractional Kelly
Full Kelly is mathematically optimal for growth, but only if you know your true win probability exactly. Nobody does. Your probability estimate is itself an estimate, and full Kelly assumes it is perfect. When your edge estimate is even slightly too high, full Kelly overbets and drawdowns get brutal.
The fix is to bet a fraction of the Kelly number:
- Full Kelly: maximum growth, but deep and frequent drawdowns. A 50% bankroll loss at some point is normal.
- Half Kelly: about 75% of the long-run growth with far less volatility. This is the common choice.
- Quarter Kelly: roughly 45% of the growth, with drawdowns small enough that most people can actually stick to the plan.
In the +120 example, half Kelly turns an 8.3% stake into about 4.2%, or $210 on a $5,000 bankroll. Still aggressive, but survivable.
Bankroll size for arbs and middles vs +EV
Different strategies have different variance, so they need different sizing.
- Arbitrage locks in a small profit regardless of outcome, so per-bet variance is low. The constraint is not variance, it is having enough balance spread across books to place both sides at once. Kelly is mostly irrelevant here; you bet what the arb math tells you on each side.
- Middles usually cost a small amount most of the time and pay off big occasionally. Treat the rare hit like a long-shot payout and size the cost accordingly.
- +EV has the highest variance of the three. Single bets lose often even when the price is right, so this is where fractional Kelly matters most.
The practical takeaway: an arb bankroll is about coverage across books, while a +EV bankroll is about surviving long losing stretches.
Common bankroll mistakes
- Oversizing on a "lock." No single bet is a lock. The biggest edges on screen are more often stale lines or data errors than free money, and they deserve smaller stakes, not bigger ones.
- Chasing losses. Doubling stakes to recover is the opposite of percentage staking. It increases your bet exactly when your bankroll has shrunk.
- Ignoring correlation. Three bets on the same game outcome are closer to one big bet than three independent ones. Kelly assumes independence, so correlated bets should be sized down.
- Not rounding stakes. Calculator-perfect amounts like $213.47 stand out to a book's risk system. Round to human numbers before you click bet, which also ties into avoiding limits.
- Recalculating the bankroll too often. Resizing every single bet to the dollar is noise. Resetting your unit weekly or after a meaningful swing is enough.
Final takeaway
Bankroll management is the boring half of betting that decides whether the exciting half ever pays off. Set a dedicated bankroll, pick a percentage or fractional Kelly approach, and size every bet to survive a long cold streak.
Edge tells you which bets to make. Sizing tells you how much, and it is what keeps you in the game long enough for the edge to show up. The +EV feed gives you the Kelly stake for each bet, the Arbs and Middles feeds handle the lower-variance plays, and How to Avoid Getting Limited covers keeping your accounts open long enough to use all of it.