The Market Gazette · Sizing Edition Vol I · No. 1 Math only. No advice.

Position Sizing Calculator

Four models. One math tool. Bring your own risk framework.

Not financial advice. This tool does only math. It does not know your situation, your tax liability, or your strategy. The outputs are arithmetic, not recommendations. Position sizing without a tested edge is just slower losing. Pair this calculator with your own backtested rules. Past performance is not indicative of future results. Asset-class agnostic; works for stocks, crypto, options, futures, forex, or anything else with a price and a stop. Consult a licensed advisor for advice tailored to your circumstances.

Position

Account and trade parameters.

Account

Account size (USD or any currency) Total capital allocated to this strategy

Trade setup

Entry price Per unit (share, contract, coin) Stop loss price Where you'd exit a losing trade

Fixed % risk model

Risk per trade (% of account) 1% to 2% is conventional for most strategies

Kelly criterion inputs

Win rate (%) From your backtest or live track record Avg win / avg loss ratio Reward-to-risk ratio of historical trades

Kelly fraction (safety divisor) Full Kelly is too aggressive; 0.25 to 0.5 is common

Volatility-adjusted (ATR-based)

ATR (Average True Range) 14-day ATR is common ATR multiplier for stop Usually 1.5x to 3x

II.

Sizes

Four sizing models on the same trade.

1. Fixed % Risk Conservative

Risk a fixed percentage of account on each trade. Most universally used model.

Units

109

shares / contracts

Dollar exposure

$5,287

total notional

Risk if stopped

$250

1.00% of account

2. Kelly Criterion (fractional) Classical

Optimizes long-term capital growth. Use a fraction (0.25 or 0.5); full Kelly draws down too hard.

Units

131

shares / contracts

Dollar exposure

$6,353

total notional

Kelly %

1.20%

full Kelly: 4.80%

3. Volatility-Adjusted (ATR) Adaptive

Sizes positions based on instrument volatility. Higher ATR = smaller position. Stop derived from ATR.

Units

at ATR-based stop

Implied stop

$44.80

$3.70 below entry

Dollar exposure

$3,298

total notional

4. Fixed Fractional Compounding

A fixed percent of account size per position regardless of stop distance. Simple, scales with growth.

Units

103

at 20% of account

Dollar exposure

$5,000

20.00% of account

Risk if stopped

$237

0.95% of account

How to read this. Different models give different sizes on the same trade. Smaller is more conservative. Larger may compound faster but draws down harder when the strategy goes through a losing streak. The "correct" model depends on your edge, your psychology, and your account size. Most retail traders should not exceed 2% account risk per trade and should use no more than fractional Kelly at 0.25.