The fastest way to lose all your money betting isn’t making bad picks — it’s betting the right picks in the wrong amounts. You can be sharper than the market and still go broke if a normal cold streak catches you with too much on the line. This course is about the part of betting almost no beginner thinks about and almost every winning bettor obsesses over: how much to put on each play. Get sizing right and you give your edge time to work. Get it wrong and the edge never matters.
What a bankroll actually is
Your bankroll is a fixed pool of money set aside only for betting — money you have genuinely decided you can afford to lose. It is not your rent, not your grocery budget, not money you’ll need next month. It lives separate from your living expenses, ideally in its own account or at least its own clearly-tracked balance.
Keeping it separate does two things. First, it caps your downside: the worst case is losing the bankroll, not your financial stability. Second, it lets you size bets with a clear head, because every bet is measured against one known number instead of against how you feel about your bank balance this week.
The unit system
Instead of betting random dollar amounts that swing with your mood, you bet in units. A unit is a single standardized bet size — a fixed percentage of your bankroll. The convention is 1 unit = 1% of your bankroll. Common practice ranges from 1% to 3%; conservative bettors stick to 1–2%.
The unit formula
1 unit = bankroll × (1% to 2%)Every bet is then measured in units, not dollars: a “1-unit play” and a “2-unit play” mean the same thing for everyone, no matter how big their bankroll is.
Talking in units strips emotion out of the decision. “I love this game” stops being a dollar figure you invent on the spot and becomes, at most, a fraction of a unit more than usual — if you allow that at all.
Flat betting: bet the same on everything
Flat betting means staking the same unit on every single play, regardless of how confident you feel. The “lock of the week” gets 1 unit. The game you’re only mildly interested in gets 1 unit. You resist the urge to size up on the bets that feel certain, because certain is a feeling, not a probability — and feelings are exactly what blow up bankrolls.
Advanced bettors do sometimes vary stake by the size of their edge — a method called fractional Kelly that ties bet size to measured value. That’s a real tool, but it only works once you can estimate your edge honestly, and it punishes overconfidence brutally. We cover it in Course 15. Until then, start flat. Flat betting is forgiving, simple, and almost impossible to misuse.
Why units stay small: variance and risk of ruin
Here’s the uncomfortable truth that small units are designed to survive: variance is real, and it’s harsher than people expect. Even a genuinely winning bettor hitting 55% of their bets — a strong long-run number — will run into long losing streaks along the way. Coin-flip-level swings happen to winners constantly. Winning overall does not mean winning in order.
That’s where risk of ruin comes in. In plain terms: if your bets are too big relative to your bankroll, a perfectly normal cold streak can wipe you out before your edge ever gets a chance to show up. Once the bankroll is gone, it doesn’t matter that you would have won over the next 200 bets — you’re not betting them. Small units lower your risk of ruin to near zero. They keep you in the game long enough for the math to play out in your favor.
Sizing in action
Two bettors make the exact same picks. The only difference is how much they stake.
Same picks, opposite outcomes
Both start with a $2,000 bankroll and hit a normal 10-bet losing streak.
- Bettor A — 1 unit = $20 (1%). Ten losses = −$200, or 10% of the roll. Annoying, fully recoverable. Bankroll still at $1,800, still betting.
- Bettor B — $200 per bet (10%). Ten losses = −$2,000. That’s 100% of the bankroll. Bettor B is broke and done.
Identical picks. Identical bad luck. One bettor shrugs and keeps going; the other is wiped out — purely because of sizing.
Resize as your bankroll moves
A unit is a percentage, not a permanent dollar amount. As your bankroll grows or shrinks, recompute it so your sizing stays proportional. A practical habit is to review your unit on a set schedule — say once a month — rather than after every win or loss.
If a $2,000 roll grows to $3,000, your 1% unit moves from $20 to $30 and your bets scale up with your success. If it drops to $1,200, your unit drops to $12, automatically shrinking your exposure exactly when you most need protection. Resizing on a schedule (instead of mid-streak) keeps you from chasing — bumping your unit up the moment you’re losing is the opposite of what the system is for.
Common mistakes
- No separate bankroll. Betting out of your checking account means every bet is sized by anxiety, not by a plan.
- Chasing losses with bigger bets. Doubling up to “win it back” is how a manageable streak turns into a wipeout.
- Oversizing the “lock of the week.” The bets you’re most sure of are exactly the ones that punish you hardest when they miss.
- Scaling stakes by emotion or confidence. How a game feels has nothing to do with how much you should risk.
- Never recomputing the unit. A static dollar amount drifts out of proportion as your bankroll changes in either direction.
Key takeaways
- A bankroll is money set aside only for betting, kept separate from living expenses.
- One unit is a fixed slice of that bankroll — typically 1%, conservatively 1–2%.
- Flat-bet the same unit on every play; small units are what survive normal losing streaks.
- Recompute your unit on a schedule so sizing always stays proportional to the roll.