Position Sizing Methods Compared: Which Is Best?

The same strategy with different sizing rules produces wildly different outcomes. Position sizing is where edge meets survival.

Position sizing is how you decide how much to trade. The method you choose changes your returns, your drawdowns, and your odds of blowing the account. Here are five methods compared.

1. Fixed fractional (risk a constant %)

Risk the same percentage of your current account on every trade. As the account grows, position size grows; as it shrinks, risk shrinks.

Pros	Cons
Drives risk of ruin toward zero	Slower compounding than aggressive methods
Auto-adjusts to account size	Tiny on small accounts
Survives long losing streaks	Requires recalculating each trade

Best for: Almost everyone, especially beginners. The default recommendation.

2. Fixed lot (constant share/contract count)

Trade 100 shares every time, regardless of account size or stop distance.

Pros	Cons
Simplest to execute	Risk varies wildly per trade
Easy to backtest	Same-size bet on a tight stop and a wide stop means very different risk
No calculation needed	Can blow the account in a bad streak

Best for: Pure execution practice on paper. Not recommended for live accounts.

3. Kelly Criterion

Risk the mathematically optimal fraction to maximize long-term growth: Kelly% = W − (1−W)/R.

Pros	Cons
Maximizes theoretical growth	Full Kelly has brutal drawdowns
Mathematically grounded	Inputs (win rate, R) must be accurate
Scales with edge strength	Edge estimates are unreliable in practice

Best for: Use fractional Kelly (quarter-Kelly) as a ceiling on your risk, never as a target. See the Kelly Criterion guide.

4. Volatility-based (ATR scaling)

Risk a constant percentage, but adjust position size so the distance to stop equals a fixed multiple of ATR. Effectively: risk the same %, with stops that adapt to volatility.

Pros	Cons
Adapts to market conditions	Requires computing ATR
Stops sit outside normal noise	More complex than fixed fractional
Works across instruments	Stops can be wide on volatile assets

Best for: Discretionary traders using ATR-based stops. A refinement of fixed fractional.

5. Martingale (double after losses)

Double position size after each loss to "recover" the previous loss when you eventually win.

Pros	Cons
None worth the risk	Mathematically guaranteed to eventually wipe the account
	Requires infinite capital to be safe
	Loses to table limits / margin calls

Best for: Nobody. This is a known ruin strategy dressed up as a "system." Avoid completely.

Comparison table

Method	Safety	Growth	Complexity	Recommendation
Fixed fractional	High	Moderate	Low	Default for most traders
Fixed lot	Low	Low	Lowest	Paper trading only
Kelly (fractional)	Medium	High	High	Use as a ceiling
Volatility-based	High	Moderate-high	Medium	Best for discretionary traders
Martingale	None	—	Low	Never

Which is best?

For 90% of traders, the answer is fixed fractional at 1%–2% risk per trade, optionally refined with volatility-based stops. It's the simplest method that's also mathematically sound — and the only one that survives both your worst losing streak and your worst psychological moments.

The remaining 10% — typically systematic trend followers with large samples — can layer fractional Kelly on top as a sanity check on their sizing. Even they cap at 1%–2% in practice.

How to start

Pick fixed fractional
Set risk at 1% (0.5% if you're new)
Use the position size calculator every trade
Log your actual risk in a journal
After 200 trades, re-evaluate — only then consider a more sophisticated method

The best position sizing method is the one you'll actually follow for 1,000 trades. Fixed fractional wins that test.