Position Sizing: Deriving the Right Share Count from Risk and Stop Distance
Don't guess how much to buy — derive it from your risk. The calm approach.
7 min read
Many beginners first decide how many contracts or shares to buy, and only then look at where the stop sits. That order needs to be reversed. Position size isn't a gut feeling — it's the result of a small calculation: first you set the most you're willing to lose on this one trade, and from that you derive how large the position is even allowed to be. That way your risk stays the same whether the stop is close or far away.
In this guide we'll walk through the calculation step by step: your account risk (a fixed percentage of your capital) times your capital gives you your risk amount in euros. You divide that amount by the stop distance, and there's your share count. We'll look at why an always-identical fixed size is deceptive and how the whole thing ties into money management. This isn't about a strategy, but about the understanding behind every sensible position size.
The Calculation — Step by Step
The core consists of three values: your capital, your account risk, and the stop distance. Account risk is the percentage of your capital that you're willing to put on the line in a single trade at most. Many traders choose a small value such as 1 percent for this — not because it's a guarantee, but because a single misjudgment then costs only a small part of the account.
The stop distance is the gap between your entry and your stop-loss — the level at which you end the trade if it runs against you. You determine this distance from the chart, not from the share count you'd like to trade. Only once both values are set do you work out the position.
- Step 1 — risk amount in euros: capital times percentage. Example: 10,000 euros of capital times 1 percent gives 100 euros that you're willing to risk on this trade.
- Step 2 — determine the stop distance: how far is your stop from the entry? Example: you buy a share at 50 euros and set the stop at 48 euros — that's 2 euros of distance per share.
- Step 3 — derive the share count: risk amount divided by stop distance. 100 euros divided by 2 euros gives 50 shares.
- Cross-check: 50 shares times 2 euros of loss per share is exactly 100 euros — your planned risk. The numbers add up.
Why a Fixed Share Count Is Deceptive
Suppose you always trade 50 shares, no matter what the chart looks like. On one trade your stop is 2 euros away, on the next it's 6 euros. With the same fixed share count you risk 100 euros in the first case but 300 euros in the second — without consciously deciding to. So your risk swings wildly, even though the position looks the same.
This is exactly where the danger lies: a fixed size couples your risk to the randomness of the stop distance. With wide stops you secretly risk far more than you'd like; with tight stops far less. Calculating via account risk turns this around. It adjusts the share count so that the euro amount at risk always stays the same — sometimes that's more shares, sometimes fewer. That's the difference between a constant position and a constant risk.
This brings us to money management, the overarching framework. Money management means protecting your capital across many trades rather than maximizing individual gains. Position size is the tool you use to put that rule into practice on the individual trade. There's no such thing as thoughtful money management without clean position sizing — the two belong together.
Common Misconceptions
- ✕Setting the share count first and adjusting the stop to fit it — the right order is the reverse: stop from the chart, share count from the risk.
- ✕Always trading the same fixed size and overlooking that a wide stop quietly multiplies the actual risk.
- ✕On leveraged products, futures, or CFDs, thinking of the stop distance only in price points and forgetting to convert it into real euros via the point value.
- ✕Setting the risk percentage so high that just a few losing trades in a row wipe out a large part of the account.
Put It Into Practice with FlowTrader
In FlowTrader you record for each trade how large your position was, where your stop sat, and what percentage of your capital you actually risked. A calculator can spit out the share count in seconds, but only your journal shows you over time whether you're really sticking to your own risk rule — or whether you quietly size up on certain trades. After a few weeks you'll see in black and white how constant your risk per trade really is. No tool can hand you the understanding behind it; it only makes visible what you decided yourself.
Try FlowTrader for freeUseful Calculators
Turn what you've learned straight into numbers with the free calculators.