Most traders focus on entries and exits. But the most important skill in trading is position sizing — deciding how much to risk on each trade. Get this right, and you can be wrong more than 50% of the time and still be profitable.
Why Position Sizing Matters
Imagine two traders with identical strategies:
| Trade | Trader A (risks 2%) | Trader B (risks 10%) |
|---|---|---|
| Loss 1 | –2% | –10% |
| Loss 2 | –2% | –10% |
| Loss 3 | –2% | –10% |
| Loss 4 | –2% | –10% |
| Loss 5 | –2% | –10% |
| Total drawdown | –10% | –50% |
Trader A is down 10% and can easily recover. Trader B is down 50% and needs a 100% gain to break even.
This is why professional traders never risk more than 1–2% of their account on a single trade.
The 1% Rule
Risk no more than 1% of your total account on any single trade.
| Account Size | Max Risk per Trade |
|---|---|
| $1,000 | $10 |
| $10,000 | $100 |
| $100,000 | $1,000 |
This doesn’t mean you can only enter with $100 worth of Bitcoin. It means your potential loss on the trade is capped at $100.
How to Calculate Position Size
Position Size = (Account × Risk %) / (Entry – Stop Loss)
Example:
- Account: $10,000
- Risk per trade: 1% ($100)
- Entry: $50,000 (BTC)
- Stop loss: $48,000 (4% below)
Position size = ($10,000 × 0.01) / ($50,000 – $48,000) Position size = $100 / $2,000 Position size = 0.05 BTC
You would buy 0.05 BTC at $50,000. If stopped out at $48,000, you lose $100 (1% of account).
The Kelly Criterion
For more advanced traders, the Kelly Criterion helps optimise position size based on your historical win rate and risk/reward ratio.
Kelly % = W – [(1 – W) / R]
Where:
- W = Win rate (e.g., 0.55 for 55%)
- R = Risk/reward ratio (e.g., 2 for 2:1)
Example: 55% win rate, 2:1 risk/reward
Kelly % = 0.55 – [(1 – 0.55) / 2] Kelly % = 0.55 – 0.225 Kelly % = 0.325 (32.5%)
The Kelly Criterion says to risk 32.5% per trade. Most traders use fractional Kelly (25–50% of the Kelly value) to be conservative.
Scaling In vs All-At-Once
| Approach | Pros | Cons |
|---|---|---|
| All at once | Simple, less complexity | Full risk from start |
| Scale in (3 entries) | Better average entry | Partial exposure if reversal is quick |
| Scale out (partial exits) | Locks in profits, reduces risk | May miss full move |
Most professionals scale in with 2–3 entries and scale out with 2–3 exits.
Common Position Sizing Mistakes
| Mistake | Why It’s Dangerous |
|---|---|
| Fixed position size (e.g., always 0.1 BTC) | Ignores stop distance — risk varies wildly |
| Increasing size after losses | Revenge trading compounds losses |
| Decreasing size after wins | Letting fear cap your success |
| Ignoring correlation | 5 uncorrelated 2% risks = 10% total risk |
The Correlation Trap
If you have 5 open positions that are all correlated (e.g., BTC, ETH, SOL), a crypto-wide crash hits all of them. Your “1% risk per trade” becomes 5% total real risk.
Solution: Reduce position sizes when positions are correlated. Or use different asset classes.
Bottom Line
Position sizing is the single most important skill in trading. Use the 1% rule to survive. Scale in and out to optimise entries and exits. Track your win rate and risk/reward to refine sizing over time. And never increase size after a loss — that’s how accounts get blown up.