Position Sizing Error — Definition, Examples, How to Fix

What it is

Inconsistent position sizing is one of the most reliable predictors of poor returns. Without a fixed rule (e.g., 0.5% of account per trade, or 1R based on stop distance), the trader sizes by emotion: bigger when confident, smaller when uncertain. The result is that the worst-sized trades are systematically the worst-outcome trades, because confidence is a poor predictor of trade quality.

What it looks like

• Sizing 200% of normal on a "high-conviction" trade that loses.
• Sizing 30% of normal on a setup that ends up being the day's best.
• Letting "feel" decide size instead of stop-distance.

Why it costs you money

When position size correlates negatively with outcome (which it usually does for emotional sizing), the strategy's positive expectancy is destroyed. Even a 60% win-rate setup loses money if you size big on losers and small on winners.

How TradeSaath detects this

TradeSaath tracks position-size variance against your account median. Trades sized >150% or <50% of your median are flagged, with the win rate of those outliers compared to baseline.

How to fix it

1. Use a fixed-fractional sizing rule (% of equity per trade).
2. Size by stop distance — trades with wider stops should have smaller position size.
3. Pre-compute size before market open; don't re-decide intraday.
4. Track size variance monthly — should stay within 20% of median.

Related

Is position sizing error costing you money?

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