The 1-2% rule says that on any single trade, the most you are willing to lose if the stop is hit should be no more than 1-2% of your total account equity. It is a risk cap, not a position-size cap: a $25,000 account using 2% risks at most $500 per trade regardless of whether that buys 50 shares or 5,000. The rule is the cornerstone of fixed-fractional position sizing and is the single most cited survivability heuristic in retail trading.

Why it works

The point of the rule is to make a string of losses survivable rather than fatal. Drawdowns from consecutive losses compound multiplicatively, not additively, because each loss is taken on a smaller balance. At 2% per trade, after 10 straight losers the account retains 0.98^10 ≈ 0.817 of its value — roughly an 18.3% drawdown, not 20%. At 1%, the same 10-loss streak leaves 0.99^10 ≈ 0.904, about a 9.6% drawdown. Contrast that with reckless sizing: 10% per trade over the same 10 losses retains only 0.90^10 ≈ 0.349 — a 65% loss that mathematically cannot recover within a realistic horizon. Recovery is asymmetric: an 18.3% drawdown requires a ~22.4% gain to get back to even (1/0.817 − 1), while a 65% drawdown needs ~186%.

Losing streaks are not edge cases — for any strategy with imperfect accuracy they are statistically guaranteed over enough trades (at a 50% hit rate, five losses in a row occurs roughly once every 32 sequences). Keeping each loss small is what keeps the account in the game long enough for a positive edge to express itself. This is the practical face of risk of ruin: lower per-trade risk drives the probability of catastrophic loss sharply down.

How it's applied

Application is a three-step calculation that runs backward from the dollar risk:

1. Max risk dollars = account equity × risk% (e.g. $25,000 × 2% = $500). 2. Risk per share = entry price − stop price (e.g. $50 entry, $45 stop = $5/share). 3. Share size = max risk dollars ÷ risk per share (e.g. $500 ÷ $5 = 100 shares).

The stop distance — not a fixed share count or dollar amount — determines size. A wider stop forces a smaller position; a tighter stop allows a larger one, but the risk stays constant. See the sibling node Position-Size Formula (risk ÷ stop distance) for the full derivation.

How it's used in practice

In practice traders pick a fixed fraction and apply it consistently: 1% is the conservative standard (institutional desks and risk-of-ruin literature favor it), 2% is the moderate ceiling most retail guidance treats as the upper bound. Because the percentage is applied to current equity, position sizes scale up automatically as the account grows and shrink during drawdowns — a built-in deleveraging mechanism. Many traders deliberately cut the fraction further (to 0.5-1%) during losing streaks or volatile regimes, and only return to the full fraction once equity recovers.

Strengths & limitations

The rule's strength is also its boundary: it is necessary but not sufficient. Capping per-trade risk guarantees you survive a streak, but it creates no edge — a strategy with negative expectancy still bleeds out slowly under perfect 1% sizing; the rule only controls how fast. It must be paired with a method that has positive expectancy and with portfolio-level controls (correlation and total open risk / "heat"), since ten uncorrelated 2% positions is very different from ten that all crash together.

The #1 misuse is overriding the rule for "high-conviction" trades — risking 4-5% because a setup looks unmissable. Conviction is uncorrelated with outcome on any single trade, and the oversized loser that follows is exactly the kind of event the rule exists to prevent. The discipline is worthless if it is abandoned precisely when it matters.

System relevance

Augustus enforces this rule at the engine level: per-trade risk is capped as a fixed fraction of equity, so no single signal — however strong its score — can size beyond the configured ceiling. This makes survivability a structural property of the system rather than a matter of trader willpower.

Sources

• Van Tharp Institute — Position Sizing Strategies and Risk Management (vantharpinstitute.com): position sizing as the primary determinant of survival.
• Investopedia / CME Group — The 2% Rule (cmegroup.com education): the equity × risk% → risk-per-share → share-size calculation.
• Risk-of-ruin literature — drawdown compounding and survivability (daytradingtoolkit.com, traderssecondbrain.com, thearcalabs.com): 2% / 10-loss ≈ 18.3% drawdown; lower fraction drives risk of ruin below 5%.