Position Sizing — The %-Risk Model That Saves Accounts
Most conversations about trading revolve around where to enter. Meanwhile, accounts get blown up by an entirely different question: how much to buy. You can have a decent strategy and still zero out your account if you size positions "by feel" — and, conversely, an average strategy with iron risk control can survive for years.
Position sizing — choosing how big a position to take — is the least glamorous and simultaneously the most important part of a trade plan. In this article we break down the percentage-risk model (the so-called 1% model), show the position-size formula derived from the stop loss, and run the whole thing on a concrete BTC example.
Educational framework: this article is for educational purposes only and is not investment advice. Trading cryptocurrencies and leveraged instruments carries the risk of losing your entire capital. Never risk money whose loss would destabilize your financial situation.
What Position Sizing Is
Position size answers the question: what notional can I open so that, if I'm wrong, I lose exactly as much as I already accepted in advance? The starting point isn't "how much free cash do I have," but "how much am I willing to hand the market if I'm wrong."
In practice you'll encounter four basic approaches:
- Fixed amount — e.g., $500 on every trade. Simple, but ignores both account growth and instrument volatility.
- Percentage of capital (the %-risk model) — you risk a fixed percentage of the current account value, usually 0.5-2%. The risk amount grows and shrinks with the account — this is the heart of this article.
- Volatility-based sizing (ATR) — the ATR indicator sets the stop-loss distance, so on a choppy market the position automatically shrinks, and on a calm one it grows.
- Sizing from risk-reward — you pick the position so that the ratio of potential gain to risk meets a minimum threshold (e.g., 2:1); more in the article on risk-reward.
The percentage-risk model is the most popular for a reason: it scales automatically, it's trivial to calculate, and — most importantly — it mathematically protects against the thing that kills the most accounts: a losing streak hit with positions that were too large.
What the Numbers Say
The single most important table in all of risk management is the cost of climbing out of a drawdown. Percentages aren't symmetric — the deeper you fall, the disproportionately more you need to recover:
| Drawdown | Gain needed to break even |
|---|---|
| -10% | +11% |
| -20% | +25% |
| -30% | +43% |
| -50% | +100% |
| -70% | +233% |
The flip side: what a streak of 10 losing trades in a row does to an account (and at 50% accuracy, a streak of 10 losses happens more often statistically than intuition suggests):
| Risk per trade | Account after 10 consecutive losses |
|---|---|
| 1% | -9.6% |
| 2% | -18.3% |
| 5% | -40.1% |
| 10% | -65.1% |
At 1% risk, ten losses in a row is a scratch. At 10%, the account is practically beyond repair (you'd need +187% just to get back to zero). That's why the widely cited "1-2% rule" gets repeated so stubbornly in the literature: it doesn't maximize profit, it maximizes the odds that you'll still be around by the time your edge gets a chance to play out.
As always: the numbers above are pure arithmetic, but any reference to strategy results or backtests in this series carries the same caveat — past results don't guarantee future ones, and figures cited from external sources (e.g., QuantifiedStrategies) are worth verifying at the source before you rely on them.
How to Apply It Step by Step
The %-risk model comes down to three steps and one formula.
Step 1. Set the risk amount. Decide what percentage of your account you're handing over in the worst-case single-trade scenario. Let's go with 1%.
Step 2. Determine the stop loss BEFORE you calculate the position. The stop comes from analysis (a technical level, ATR — details in the article on stop losses), never from "how much do I want to buy." The order is non-negotiable: stop first, position size second.
Step 3. Calculate the position size from the formula:
position size = (capital × % risk) / (entry price − stop-loss price)Numerical Example on BTC
- Account: $20,000
- Risk per trade: 1% = $200
- Long entry BTC: $100,000
- Stop loss: $97,000 (3% below entry, under a local support level)
Risk per 1 BTC = 100,000 − 97,000 = $3,000.
Position size = 200 / 3,000 = 0.0667 BTC, a notional of roughly $6,667.
If price drops to 97,000 and the stop triggers, you lose 0.0667 × 3,000 ≈ $200 — exactly the planned 1% of the account. Not a cent more.
Notice the mechanics: if you set a tighter stop at 98,500 (1.5% below entry), the position grows to 200 / 1,500 = 0.1333 BTC (~$13,333 notional) — while the dollar risk stays the same $200. A tight stop means a larger position; a wide stop means a smaller position. The risk amount is fixed; only the notional changes.
[Chart coming soon: BTC D1 chart showing an entry at 100,000, a stop loss at 97,000 below support, and a caption "1% of account = $200 regardless of SL width"]
The Volatility Variant (ATR)
Instead of a technical level you can base the stop on ATR, e.g., SL = entry − 2×ATR(14). With ATR on BTC at $2,800, the stop lands $5,600 below entry, so the position = 200 / 5,600 = 0.0357 BTC. A more volatile market → wider stop → automatically smaller position. It's the simplest way to keep risk comparable between calm BTC and a choppy altcoin.
Rules for Running the System
- Calculate the risk percentage from the current account value, not the starting balance — after losses, positions shrink on their own; after gains, they grow.
- A daily/weekly limit (e.g., 3 losing trades = done for the day) protects against a revenge-trading spiral.
- Never increase position size while a losing trade is still open — that's no longer sizing, it's averaging down on despair (we cover why that ends badly in the article on martingale).
Think in Units of R, Not Dollars
Once the risk amount is fixed, the natural unit for results stops being the dollar and becomes R — one planned unit of risk. The trade from the example above, closed at the stop, is -1R; closed $600 higher, it's +3R. Recording results this way in a trading journal has two advantages. First, it inoculates you against illusions: "+$450" sounds great until you realize it's +0.5R on a risk that was set up to deliver 3R — meaning you exited too early. Second, it lets you compare results independent of account size and instrument: 40 trades averaging +0.3R is hard information about system quality that a list of dollar amounts will never give you.
There's a third benefit, a psychological one: since every loss is by definition -1R, a single stop stops being a drama — it becomes the cost of doing business, planned down to the cent before you even entered. That predictability, not some secret formula, is the real reason experienced traders talk about position sizing so boringly and so relentlessly.
When It Doesn't Work and the Most Common Traps
The %-risk model isn't a magic shield. Here are the situations where it breaks down — and the mistakes that disarm it:
- Price gaps and slippage. The formula assumes the stop fills at your price. On crypto, during violent moves (or on illiquid altcoins), execution can land well below your level — the real loss exceeds the planned 1%. A partial fix: smaller positions on illiquid markets and avoiding trades right before major macro data.
- Correlated positions. Three 1% positions on BTC, ETH and SOL are often not 3 separate 1% risks — they're one 3% risk, because in a crash the entire crypto market drops together. Cap the combined risk of correlated positions (e.g., max 3% on "market direction").
- Percentage risk without a stop loss. The formula requires a defined emergency exit. A "mental stop" you shift in your head switches off the whole equation.
- Raising the percentage after a win streak. Overconfidence after a good run is a classic — two oversized positions can give back the gains from twenty disciplined ones.
- Too small an account vs. minimum lot sizes. If 1% risk forces a position smaller than the exchange's minimum lot, you're actually risking more than the model assumes — that's a sign the instrument is too big for your account, not that "risk needs to go up."
Position sizing won't make you right more often. It will do something more important: it will make being wrong stop being dangerous. Combined with a sensible risk-reward ratio and a consistent stop loss, it forms the foundation on which any entry strategy is worth building.
FAQ
What percentage of capital should you risk per trade?
What's the difference between risk per trade and position size?
Does leverage change how you calculate position size?
Trader and founder of Strefa Tradingu. He’s been breaking crypto down on YouTube for years — no hype, no signals, with a focus on market structure and risk management.
🎁 Grab Strefa’s free TradingView indicators
Drop your email — we’ll send you links to our free TradingView indicators plus a no-fluff starter kit. Zero spam.
You’re joining the Strefa Tradingu list. Unsubscribe with one click, anytime.Check your inbox (and the Spam/Promotions folders) and add us to your contacts.