Position Sizing

Position sizing is the step where you decide how large a single trade should be. It does not tell you what to trade, when to enter, or when to exit. It answers one narrow question: given this account and this trade idea, how many units, lots, shares, or contracts should the position be?

It helps to separate three decisions that often get blurred together. The signal decides direction. The stop decides where the idea is wrong. Position sizing decides how much money is on the line if that stop is hit. Many structured approaches treat the third decision as a risk-control input, fixed in advance, rather than something adjusted by how confident a trade feels. In those frameworks the size is derived from rules, not from conviction. This is a description of one common way of working, not a rule anyone has to follow.

A widely taught starting point is the fixed-fractional or fixed-percentage method. The idea is to decide ahead of time what fraction of the account you are willing to lose on any one trade if the stop is reached — for example, a small percentage of total equity — and then size every position so the loss at the stop equals that fixed amount.

The appeal traders often cite is consistency. Because the risk is a percentage of the current account, the currency amount shrinks after losses and grows after gains, so no single trade dominates the account. This is a description of how the method behaves, not a claim that it improves results. It does not make trades more likely to work, and it does not prevent losing streaks. It only governs how much each loss costs relative to the account at the time. The choice of percentage is a personal risk decision, and this guide does not suggest any particular figure.

The core formula is straightforward:

Position size = (account risk in currency) / (stop distance in price x value per point)

'Account risk in currency' is the fixed amount you have chosen to risk. 'Stop distance' is the gap between your entry and your stop. 'Value per point' is how much one unit of price movement is worth for the instrument you are trading — this varies by market and contract, so it has to be checked per instrument rather than assumed.

The key relationship is that stop distance and position size move in opposite directions. A wider stop forces a smaller position to keep the same currency risk; a tighter stop allows a larger one. This is why traders often set the stop based on the trade structure first, then let the size fall out of the math — rather than picking a size first and forcing a stop to fit it.

Suppose an account is 10,000 in its base currency, and the trader has decided to risk 1% per trade — so 100 of currency at risk. The trade idea places a stop 50 points away from entry, and one point is worth 1 unit of currency per unit of position.

Size = 100 / (50 x 1) = 2 units. If the stop is hit exactly at the expected price, the loss would be 50 points x 2 units = 100, which matches the 1% figure chosen.

Now widen the stop to 100 points. Size = 100 / (100 x 1) = 1 unit. The position is half the size, but the loss at the stop is still 100. The risk stayed fixed; only the size changed. Working through the arithmetic this way shows that the stop, not a gut feeling about size, is what drives the number. These figures are illustrative inputs, not a suggested risk level.

Position sizing caps the intended loss only under assumptions that do not always hold. The biggest one is that the stop fills at the price you chose. In fast or illiquid markets, price can gap past a stop or fill with slippage, so the realised loss can exceed the planned amount. Leverage adds another layer: it changes how much margin a position uses and can amplify both the size you are able to take and the consequences of an adverse move.

A few practical points traders keep in mind. Costs such as spread and commission are not part of the basic formula and eat into the result. Value per point and contract specifications differ across instruments, so a size that is correct for one market is not automatically correct for another. And running several correlated positions at the 'same' per-trade risk can stack into a much larger combined exposure than any single number suggests.

None of this makes position sizing predictive. It is a budgeting tool for risk, not a forecast. No sizing method removes the risk of loss, and all trading carries that risk. Treat the formulas here as educational illustrations of how the mechanics work, not as guidance on how much anyone should risk.

If you want to see your intended risk on a chart, a small indicator can draw a hypothetical stop level and label the currency risk implied by a stop distance, value per point, and size you type in. The snippet below is a minimal, educational example in Pine Script v6. It does not generate signals and is not an instruction to trade.

//@version=6 indicator("Risk Per Trade (educational)", overlay = true)

stopPoints = input.float(50.0, "Stop distance (points)") valuePerPoint = input.float(1.0, "Value per point") size = input.float(2.0, "Position size (units)")

riskCurrency = stopPoints valuePerPoint size stopLevel = close - stopPoints

plot(stopLevel, "Hypothetical stop", color = color.red)

if barstate.islast label.new(bar_index, stopLevel, str.tostring(riskCurrency, "#.##") + " risk", style = label.style_label_up)

The values are inputs you set, not market reads, so the plotted stop and the risk label reflect only the assumptions you typed in. The example treats a long-style stop placed below price for simplicity; real fills, costs, and gaps can differ from any drawn level. As always, this is for learning how the numbers relate — not advice, and no indicator predicts price.