The math that decides whether you survive long enough to get good.
Ask a room of new traders what they're working on and they'll say entries — the perfect signal, the magic indicator. Ask a professional and they'll talk about size. Position sizing is the quiet skill that decides everything: not whether a trade wins, but how much you have riding when it does or doesn't. Get it right and no single loss can hurt you much, so you live to take the next hundred trades. Get it wrong — bet too big chasing a fast fortune — and one bad run ends the game, no matter how good your reads were. This is the math of staying alive.
The foundational rule of risk is almost boringly simple: never risk more than a small, fixed slice of your account on any single trade — the common figure is 1%, and 2% for the more aggressive. On a $25,000 account, 1% means you structure each trade so that if it goes against you and you're stopped out, you lose about $250 — no more. That's it. It sounds too cautious to matter, until you see what it buys you: survival. At 1% risk you could be wrong ten times in a row and still hold almost 90% of your account, calm and able to keep trading. The trader risking 10% a shot is one bad week from being crippled. Small risk isn't timid — it's what keeps you in the game long enough for your edge to show up.
Here's the mechanical part, and it's a formula worth burning in. Two numbers set your size. First, your dollar risk: account times risk percent — $25,000 × 1% = $250. Second, your risk per share: the distance from your entry to your stop. Buy at $50 with a stop at $48 and you're risking $2 a share. Divide one by the other and you have your position: $250 ÷ $2 = 125 shares. Notice what just happened — you didn't buy 125 shares because it felt right; the number fell out of your account and your stop. That 125 shares is a $6,250 position, a quarter of the account, yet only $250 is actually at risk. Size is an output, never a guess. Run the machine yourself below — and mind the streak test under it.
Ten losers in a row — every trader meets that streak eventually — costs you 9.6% of the account at 1% risk. The trader risking 10% a trade is down 65% after the same streak, and needs a 187% run just to get even.
Once your risk per trade is fixed, a lovely simplification opens up: measure everything in R, where 1R is simply your initial risk. That $250 — or $2 a share — is 1R. Now a loss at your stop is −1R, always, whatever the stock or the account. A trade that runs to $56, six dollars past your $50 entry, is a +3R winner. Suddenly every trade speaks the same language. You stop thinking "I made $750" and start thinking "that was 3R," which lets you compare a cheap stock with an expensive one, judge whether your winners outrun your losers, and set targets in units of risk. Professionals live in R — it turns a messy pile of dollar figures into one clean scoreboard.
There's a brutal asymmetry that makes big bets a trap: losses hurt more than equal gains help. Lose 10% and you need about 11% to get back — no big deal. But lose 50% and you don't need 50% to recover, you need 100%, a double, just to break even. Lose 75% and you need a 300% gain. This is why blowing up is so hard to come back from, and why the size of your losses matters far more than the size of your wins. Keep every loss small — 1R, a rounding error on your account — and you never fall into the deep hole where the recovery math turns against you. The trader who risks little stays on the flat part of that curve, where a losing streak is an annoyance, not a catastrophe.
See how the pieces lock together and you'll never size randomly again. Your stop — where your idea is proven wrong — sets your risk per share. Your account and risk percent set your dollar risk. Your position size is whatever makes those two agree. That's the correct order, and it has a crucial consequence: a wider stop means a smaller position, and a tighter stop lets you size bigger for the same risk. Most beginners do it backwards — they decide how many shares they "want," bolt on a stop wherever, and end up risking wildly different amounts each trade with no idea how much is on the line. Flip it. Find your stop first, size from it, and every trade risks the same small, deliberate amount. Which is exactly why the next thing to master is where that stop belongs.
The 1% is of your account, not the position — a 125-share, $6,250 position that risks $250 is a 1% risk, not a 25% one; don't confuse position size with risk. Sizing isn't a feeling: never pick a share count first and add a stop later, or you'll risk a random amount every time. And position sizing can't rescue a bad stop — if your stop sits in a silly place, small risk just means you lose your 1% a little more slowly. Size from a sensible stop, not around a number you wish you were trading.
Fresh charts you haven't seen, drawn live and shuffled together, with a couple of “why” questions in the mix. No hints until the end. Clear 3 of 4 and the module is yours.
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