Position sizing: the 1% rule.
Civil engineers don't design bridges for the average rainfall. They design for the 100-year flood, the once-in-a-lifetime ice load, the overweight truck driving across at the wrong speed. The bridge isn't built for the day it'll be tested. It's built for the worst day it might ever be tested. Most retail traders size their positions for the average trade. Not the fifty-losses-in-a-row trade. Not the gap-down-on-Monday trade. The average. That's why so many of them disappear after a normal-feeling losing streak. Position sizing is bridge engineering. The 1% rule isn't conservative — it's the load spec that lets you survive being wrong fifty times in a row.
The base math (one paragraph)
Position size is an output, not an input. You don't decide "I'm going to buy 200 shares" or "I'll put $5,000 into this." You decide three things — your account size, your risk per trade, and where the stop goes — and the share count falls out. The formula:
shares = (account × risk%) ÷ |entry − stop|Worked example. Account: $50,000. Risk per trade: 1% = $500 max risk. Entry: $200. Stop: $198.50. Stop distance: $1.50. Max shares: $500 ÷ $1.50 = 333 shares. Position cost: 333 × $200 = $66,600 (which exceeds the account; in practice you'd use less leverage or a wider stop, but the math comes from the stop, not the bankroll). The point: the moment the stop changes, the share count changes. Same $500 of risk, ten times the share count if the stop is a tenth as far. Position size tracks stop distance. It doesn't precede it.
The dollar-amount trap
Most retail traders think in terms of "I'll buy 100 shares of NVDA" or "I'll put $5,000 into this." Both are accidentally fixed-size, regardless of stop distance. A $5,000 position with a $5 stop distance is risking $250. The same $5,000 position with a $0.50 stop is risking $25. Same dollars deployed, ten times the risk on the first one. If you're sizing by capital deployed, you're risking different amounts on every trade and you don't know it.
Swing Deck never asks "how much do you want to invest?" It asks "where's your stop?" Then it computes the position. That order matters. The dollar-amount frame puts capital at the center of the question; the stop-distance frame puts risk at the center. Capital is fuel. Risk is fire. They are not the same.
Why specifically 1%
Why 1% and not 2%, not 5%, not 0.5%? Because 1% is the number where fifty consecutive losses leaves you bruised but not broken. At 1% per trade, fifty losses in a row puts you at roughly 60% of starting capital — painful, but the math of recovery is still sane. At 2% per trade, fifty losses puts you at 36%. At 5%, fifty losses puts you at 7.7%. From 7.7% you need a 12× return to get back to even, which is a number that doesn't happen.
"But I'm not going to lose fifty in a row," the new trader says. Maybe. Maybe not. Streaks of twelve, fifteen, twenty are not unusual in real backtests of decent strategies. Twenty losses at 5% is 64% drawdown — meaning a 178% gain is required to recover. From there, the only viable path is depositing more money, which is the polite phrase for blowing up. The 1% number is calibrated against a worst-case streak, not an expected one. Bridge engineering, not weather forecasting.
The doom loop
Here's how the smart trader's account dies. Down $5,000 after a string of 1% losses. Frustrated. Wants the money back this week. Reasons: "If I size 5× larger, I can recover in one trade instead of ten." Takes a 5% position on the next setup, which is — surprise — not their best setup, because they're impatient and force-grading. Loses. Now down $7,500.
The math required to recover $7,500 from a $42,500 account base is harder than the math required to recover $5,000 from $45,000. So they size up again. 7% this time. Lose again. Down $10,475. Now they need a +27% gain just to get to even, on an account that just demonstrated it can lose three trades in a row. Most accounts that enter the doom loop don't exit it.
The 1% rule pre-empts the doom loop by removing its first ingredient: the temptation to recover quickly. At 1% you can't recover quickly. You can only recover patiently. Which sounds like a weakness and is actually the entire point.
Drawdown math is geometric, not arithmetic
Most beginners assume drawdowns and gains are symmetric. They're not. Lose 20% of your account and you need a 25% gain to get back. Lose 50%, you need 100%. Lose 75%, you need 300%. Lose 90%, you need 900%. The deeper the hole, the more nonlinear the climb.
| Drawdown | Capital remaining | Gain required to recover |
|---|---|---|
| −10% | 90% | +11% |
| −20% | 80% | +25% |
| −33% | 67% | +50% |
| −50% | 50% | +100% |
| −75% | 25% | +300% |
| −90% | 10% | +900% |
This is why the 7% portfolio sleeve gate (introduced later in the curriculum and embedded in the framework's pre-flight checks) exists. Below 7% drawdown the recovery math is mostly fine — a +7.5% gain gets you back. Above 7% the curve starts bending unpleasantly, and the psychological pressure to size up to recoup is the highest. The framework refuses new entries below the 7% line specifically because that's the zone where bad sizing decisions cluster.
Position size as a circuit breaker, not a goal
The point of the 1% rule isn't to make you rich. It's to make you uncertain in a survivable way. Every trade is allowed to be wrong. The size is calibrated so that fifty wrong trades don't end the account. That's the entire job of position sizing — to be the circuit breaker that trips before the wiring melts. Not the engine. Not the strategy. The breaker.
Think of a fire extinguisher. You don't size a fire extinguisher to fight the average house fire. You size it to fight the worst plausible fire it might ever face. Most days, it does nothing. The day it matters, it's the difference between losing a kitchen and losing a house. Position sizing is the fire extinguisher of a trading account. It does nothing on the good days. On the bad days, it's everything.
The portfolio sleeve gate (7% halt)
Per-trade sizing is one layer. Portfolio-wide sizing is another. Even at 1% per trade, ten open positions means 10% of the account at risk simultaneously if everything correlates the wrong way (which, in a market-wide sell-off, it will). The framework caps simultaneous open risk via "sleeves" — buckets of capital allocated to different ideas — and tracks the running portfolio drawdown.
At 7% portfolio drawdown from peak, the broker pre-flight chain refuses new entries by default. Why 7%? Because 7% is enough to register as "something is wrong" without being so deep that it's a psychological cliff. Below 7%, the math of recovery is benign and traders mostly behave. Above 7%, traders start sizing up, force-grading setups, abandoning the rules — exactly the doom-loop conditions described earlier. The halt isn't punishment. It's a forced pause to evaluate whether the strategy is broken or the market is just hostile that week.
What the dashboard does with it
The Position Sizer surface fires on every candidate before order placement. Inputs: ticker, current price, stop price, account snapshot. Outputs: max shares, max risk in dollars, percent of account at risk on this trade, and — critically — running portfolio risk if this trade fills alongside everything else open.
If you try to override the 1% to size up, the surface shows you concretely how many additional losing trades you can afford before hitting the 7% sleeve gate. Not as a guilt-trip — as a budget. "You're sizing this at 3%. Three more losses at this size and you'll trip the halt." That's the kind of message that makes the override feel honest, not heroic.
NVDA position at 3.0% risk — above 1.0% default. At this size, 3 more losses trips the 7% portfolio halt. Override valid? (y/n)
The real lesson
The 1% rule isn't where the money comes from. The money comes from R:R, patience, and refusing the days the watchlist hands you nothing tradeable. The 1% rule is what keeps you in the game long enough for those things to add up. Refuse to size big until the math has earned the right — and "earned the right" means not "I had three winners in a row," but "I have 200 trades in the journal and the win rate and R:R hold up."
Most retail traders treat sizing as the boring part — the math you do before the fun part. Pros treat sizing as the only part that matters. Direction is a coin you flip; size is the lever that decides whether the coin still spins next year.
Related: Lesson 4 — R:R isn't a number · Lesson 6 — Stop-loss math that survives gaps · The Position Sizer surface (docs)