Gestión de Riesgo y Psicología del Trading

Position Sizing

Q: ¿Por qué 1-2% y no 5% per trade?

Math of ruin. Con 1% per trade, 100 consecutive losses to ruin. 2% = 50 consecutive losses. 5% = 20 consecutive losses. 10% = 10 consecutive losses. Probabilistically, any strategy will produce 5-10 consecutive losses occasionally (even excellent strategies). Con 5% risk, 10 consecutive losses = 40% account drawdown (hard to recover). Con 10% risk = 65% drawdown (very hard). Con 1-2% = 5-20% drawdown (manageable). Survival mathematics dictates conservative sizing. Experience traders may go to 2-3% with proven strategy, but 1% remains foundational.

Q: ¿Cómo calculo position size con opciones?

Long options: Contracts = Risk Budget / (Premium × 100). Ejemplo: $1,000 risk, $3 premium → $1,000 / $300 = 3 contracts (max loss $900). Credit spreads: Contracts = Risk Budget / (Max Loss per Contract). Max loss = spread width × 100 - credit × 100. Ejemplo: $5 wide put credit spread, $1 credit → max loss $400 per contract. $1,000 / $400 = 2.5 contracts (round to 2). Debit spreads: Contracts = Risk Budget / (Net Debit × 100). Always calculate max loss explicitly, not just entry cost.

Q: ¿Qué hago si muchas positions son correlacionadas?

Adjust aggregate exposure. Regla: posición de sector o theme (tech, crypto, financials) no debe exceder 3-5% portfolio risk total. Con 1% per position, 3-5 positions en mismo sector. Con 2% per position, 2-3 positions. Correlation not always obvious: growth stocks correlate; small-caps correlate; international emerging markets correlate. Durante 2008 crisis, "uncorrelated" assets became correlated (everything crashed). Adjust stress scenarios. Real discipline: treat correlated positions as single exposure for risk budgeting.

Q: ¿Debo aumentar size cuando gano?

Sí, pero proportionally via compounding. Correct: si portfolio crece de $100K a $120K con 1% rule, dollar risk per trade crece de $1,000 to $1,200. Percentage rule unchanged but dollar amount grows. Incorrect: increasing percentage during winning streaks (from 1% to 2% to 5%). Esto abandon discipline y creates massive risk during eventual reversal. Amateur: feels confident, sizes up aggressively. Professional: maintains % discipline regardless of emotions. Compound growth happens naturally via portfolio appreciation at fixed %. Don't force it emocionalmente.

Q: ¿Es Kelly Criterion mejor que fixed 1%?

Mathematically yes, practically no. Kelly is optimal for growth IF you know exact win rate y R/R. En práctica, estimates are uncertain, especially en volatile markets. Kelly assumes stationary probabilities; real markets have regime changes. Full Kelly at assumed 40% is likely 30% in reality, leading to blowup. Solution: Half-Kelly (20%) or Quarter-Kelly (10%) reduces risk substantially but still aggressive. Most profesional traders use fixed fractional 1-2% as foundation, possibly Kelly-adjusted upward for very high-conviction trades. For retail traders, stick with 1-2% fixed fractional.

EN: Position Sizing / Risk Per Trade PT: Dimensionamento de Posição

La decisión más importante del trader — cuánto del capital arriesgar en cada trade individual. Position sizing determina survival del portfolio durante losing streaks; errores aquí destruyen cuentas incluso con strategy rentable. La regla 1-2% es el estándar profesional testado durante décadas.

Neutral Fuerza: Alta Tasa histórica: Position sizing es 90% de portfolio variance per Van Tharp research; disciplined 1-2% rule dramatically reduces account ruin probability Confirmación: Opcional Universal application; critical para options (defined max loss); essential para all leveraged strategies; foundation de professional trading.

Qué es Position Sizing

El Position Sizing (en portugués Dimensionamento de Posição) es la decisión de cuánto capital allocar a cada trade individual, y equivalentemente cuánto riesgo (dollar amount) asumir en cada position. Esta decisión es mathematically más importante que timing, selection, o R/R analysis porque determina la supervivencia del portfolio durante losing streaks inevitables. Un trader con strategy rentable PERO bad position sizing puede ir a la quiebra; un trader con strategy marginal PERO excellent position sizing puede sobrevivir hasta mejorar. Van Tharp en "Trade Your Way to Financial Freedom" (1998) demostró que position sizing es responsible for 90%+ de la variance en portfolio outcomes across traders con same strategy. La regla más citada del trading profesional: nunca arriesgar más de 1-2% del portfolio en un solo trade. Origen de esta regla: survival mathematics — trader con 1% risk per trade puede perder 100 trades consecutivos con solo 100% loss, pero perdería 50 trades consecutivos con only 50% account drawdown recoverable. Realistically, any 5-10 consecutive losses is possible even for rentable strategies — 1% risk per trade absorbs that y allows recovery. 2% risk is aggressive but acceptable for experienced traders. 5%+ per trade es financial suicide durante losing streaks. Position sizing ≠ position size: position sizing es risk amount, no dollar amount invested. Ejemplo: $100K portfolio con 1% risk per trade = $1,000 max loss per trade. Si stop-loss distance es $5 en AAPL at $200 entry, position = $1,000 / $5 = 200 shares × $200 = $40,000 investment (40% of portfolio invested, but only 1% at risk).

La Fórmula Básica

La fórmula de position sizing conecta risk budget, stop distance, y position size. Fórmula core: Position Size = (Portfolio × Risk %) / (Entry Price - Stop Price). Ejemplo detallado: Portfolio $100,000, target 1% risk per trade = $1,000 risk budget. Long AAPL at $180, stop at $175, distance = $5. Position Size = $1,000 / $5 = 200 shares. Capital invested = 200 × $180 = $36,000. Proporción capital a risk: $36,000 / $1,000 = 36×. Si trade succeeds (AAPL reaches target $195), profit = 200 × $15 = $3,000 (3% portfolio return). Si trade fails (AAPL stops at $175), loss = 200 × $5 = $1,000 (1% portfolio loss). Variations por tipo de instrumento: Stocks: position = risk_budget / (entry - stop). Straightforward. Options (long): since max loss = premium, formula simplifies. Position size = risk_budget / premium per contract. Ejemplo: risk $1,000, call premium $5 × 100 (contract size) = $500 per contract → 2 contracts = $1,000 risk. Options (spreads): max loss = spread width - credit (credit spreads) or debit (debit spreads). Position size = risk_budget / max loss per contract. Futures: more complex, involves tick value y margin. Risk = ticks × tick value × contracts. Multi-position portfolio: si tienes 10 positions simultáneamente, aggregate risk cannot exceed comfortable threshold. Rule: no más de 5-10% portfolio total risk at any time. Con 1% per trade, max 10 concurrent positions. Correlation considerations: 10 highly correlated positions (e.g., 10 tech stocks during market selloff) behave like 1 big position for risk purposes. Adjust position sizes downward cuando correlation is high.

Kelly Criterion vs Fixed Fractional

Existen múltiples methodologies de position sizing, cada con trade-offs. Fixed Fractional (1-2% rule): el standard profesional. Risk fixed % of portfolio per trade. Ventajas: (a) simple; (b) survival durante losing streaks garantizada; (c) compounds growth durante winning streaks (sizing grows con portfolio). Desventajas: (a) no adaptive para varying trade quality. Kelly Criterion: fórmula matemática óptima para maximum growth. Kelly % = Win Rate - (Loss Rate / R/R). Ejemplo: 60% win rate, R/R 1:2 → Kelly = 0.60 - (0.40/2) = 0.40 = 40% per trade. Problema: Kelly assumes perfect knowledge de win rate/R/R. En práctica, estimates are wrong, leading to catastrophic losses at Kelly %. Solution: Half-Kelly (Kelly% / 2) — ej. 20% per trade if Kelly says 40%. Still aggressive. Most profesionales use Quarter-Kelly (10% or less en anterior ejemplo). Volatility-Adjusted (ATR-based): position size adjusted por market volatility. Standard stop distance = 2× ATR(14). Higher vol = wider stops = smaller positions. Lower vol = tighter stops = larger positions. Adaptively maintains same risk per trade during different market regimes. Fixed Dollar: ej. always risk $500 per trade regardless de portfolio size. Simple pero doesn't scale con portfolio growth. Maximum Adverse Excursion (MAE)-based: position sized based en historical max adverse excursion during trade. Sophisticated, requires data analysis. Recomendación para retail traders: Fixed Fractional 1% rule es foundational. Master esto antes de experimentar con Kelly o ATR-based. La mayoría de account blowups ocurren con position sizing either larger than 2% per trade o inconsistent sizing (3% this trade, 8% next, 1% after losses).

Position Sizing con Opciones

El position sizing con opciones tiene nuances importantes vs. stocks. Long options (calls/puts): max loss = premium paid. Position sizing straightforward: contracts = risk_budget / premium_per_contract. Ejemplo: $1,000 risk, long call $3 premium × 100 = $300 per contract → 3 contracts. Credit spreads (bull put, bear call, iron condors): max loss = spread width - credit received. Ejemplo: $5 wide bull put spread, $1 credit, max loss = $400 per contract ($5 wide × 100 - $100 credit). $1,000 risk budget / $400 = 2.5 contracts (round down to 2). Debit spreads: max loss = net debit. Straightforward. Naked options: risk potencialmente ilimitada. Position sizing problematic — cuánto margin requires vs. potential loss is fundamentally mismatched. Avoid naked shorts; use defined-risk spreads instead. Correlation in options: 10 options contracts on same stock = 1 big exposure, not 10 small. Diversify across underlyings. Gamma / Delta considerations: complex. Options positions can have dynamic risk (gamma explodes near expiry). Position size conservatively cuando cerca de expiry (last 2-3 weeks). Common options position sizing errors: (1) Using margin power not risk: "I can buy 10 contracts with margin" — but total risk exceeds budget. (2) Ignoring max loss: calculating "cost of entry" but ignoring potential max loss of spread. (3) Over-sizing weeklies: high gamma options can swing 50-100% en day. Sizing based on expected move, not hope. (4) Using "net" instead of "gross" exposure: Iron condor "net premium" looks small but gross exposure (width × contracts × 100) can be massive. Regla práctica: for options, calculate TOTAL max loss of position (considering ALL legs). Size so that max loss = 1-2% of portfolio. Include commissions y slippage in calculation.

Psicología y Mistakes Comunes

La psicología del position sizing es donde muchos traders fracasan. (1) "Sizing up" after wins: doubling position size after consecutive winners. Natural emotionally pero destruye el risk discipline. Resultado: one big loss durante eventual losing streak wipes out gains. (2) "Averaging down" on losers: adding to losing positions. Seductive — "cheaper entry average." Real consequence: increases risk sobre losing thesis. One of most destructive behaviors en trading. (3) "Making back" losses: after losing, taking larger positions to recover quickly. Usually produces larger losses, compounding problem. (4) Revenge trading: similar to #3 but emocional — angry at market, trading to "get even." Negative expectancy inevitable. (5) Under-sizing after losing streaks: opposite problem. After 5 losers, trader feels "cold streak" y reduces size aggressively (0.5% or less per trade). Misses eventual mean reversion winners. (6) Over-sizing "high conviction" trades: "this one is different, I KNOW it will work." Violating sizing discipline based on feelings. Frequently wrong. (7) Ignoring correlation: 10 tech stocks during crash = 10 × 1% = 10% portfolio loss in single day (should be no more than ~3% aggregate tech exposure). Discipline framework: (1) Written rules BEFORE trading: exact sizing percentage, correlation adjustments, position concentration limits. (2) Journal every trade: planned vs. actual position size. Identify deviations. (3) Auto-stop when violation detected: if sizing exceeds rules, close position or refuse trade. (4) Review monthly: aggregated risk, concentration, correlation. Adjust forward. Van Tharp insight: "Position sizing is 90% of your results." Mastering this one concept properly — combined with discipline to adhere to it — is more important than any indicator, pattern, or strategy.

Métodos de Position Sizing Comparados

Cada método tiene trade-offs de complejidad vs. adaptiveness.

Método	Risk Per Trade	Complexity	Best For
Fixed Fractional 1%	1% portfolio	Baja	Foundation for all traders
Fixed Fractional 2%	2% portfolio	Baja	Experienced con proven strategy
Kelly Criterion (full)	Variable (high)	Media	Theoretical optimum
Half-Kelly	Kelly % / 2	Media	Less aggressive Kelly variant
Volatility-Adjusted (ATR)	Variable inversely con vol	Alta	Multi-market traders
Fixed Dollar	Absolute $ amount	Baja	Small accounts, simplicity

Preguntas Frecuentes

¿Por qué 1-2% y no 5% per trade?

Math of ruin. Con 1% per trade, 100 consecutive losses to ruin. 2% = 50 consecutive losses. 5% = 20 consecutive losses. 10% = 10 consecutive losses. Probabilistically, any strategy will produce 5-10 consecutive losses occasionally (even excellent strategies). Con 5% risk, 10 consecutive losses = 40% account drawdown (hard to recover). Con 10% risk = 65% drawdown (very hard). Con 1-2% = 5-20% drawdown (manageable). Survival mathematics dictates conservative sizing. Experience traders may go to 2-3% with proven strategy, but 1% remains foundational.

¿Cómo calculo position size con opciones?

Long options: Contracts = Risk Budget / (Premium × 100). Ejemplo: $1,000 risk, $3 premium → $1,000 / $300 = 3 contracts (max loss $900). Credit spreads: Contracts = Risk Budget / (Max Loss per Contract). Max loss = spread width × 100 - credit × 100. Ejemplo: $5 wide put credit spread, $1 credit → max loss $400 per contract. $1,000 / $400 = 2.5 contracts (round to 2). Debit spreads: Contracts = Risk Budget / (Net Debit × 100). Always calculate max loss explicitly, not just entry cost.

¿Qué hago si muchas positions son correlacionadas?

Adjust aggregate exposure. Regla: posición de sector o theme (tech, crypto, financials) no debe exceder 3-5% portfolio risk total. Con 1% per position, 3-5 positions en mismo sector. Con 2% per position, 2-3 positions. Correlation not always obvious: growth stocks correlate; small-caps correlate; international emerging markets correlate. Durante 2008 crisis, "uncorrelated" assets became correlated (everything crashed). Adjust stress scenarios. Real discipline: treat correlated positions as single exposure for risk budgeting.

¿Debo aumentar size cuando gano?

Sí, pero proportionally via compounding. Correct: si portfolio crece de $100K a $120K con 1% rule, dollar risk per trade crece de $1,000 to $1,200. Percentage rule unchanged but dollar amount grows. Incorrect: increasing percentage during winning streaks (from 1% to 2% to 5%). Esto abandon discipline y creates massive risk during eventual reversal. Amateur: feels confident, sizes up aggressively. Professional: maintains % discipline regardless of emotions. Compound growth happens naturally via portfolio appreciation at fixed %. Don't force it emocionalmente.

¿Es Kelly Criterion mejor que fixed 1%?

Mathematically yes, practically no. Kelly is optimal for growth IF you know exact win rate y R/R. En práctica, estimates are uncertain, especially en volatile markets. Kelly assumes stationary probabilities; real markets have regime changes. Full Kelly at assumed 40% is likely 30% in reality, leading to blowup. Solution: Half-Kelly (20%) or Quarter-Kelly (10%) reduces risk substantially but still aggressive. Most profesional traders use fixed fractional 1-2% as foundation, possibly Kelly-adjusted upward for very high-conviction trades. For retail traders, stick with 1-2% fixed fractional.