How to Size a Position: The 1% Risk Rule

The 1% risk rule is a core principle of capital management: on any single trade, you risk no more than 1% of your total account. Position size is then driven by the distance to your stop-loss, not by how much you would like to buy. Trading carries a high level of risk, and most beginners lose money, so protecting capital matters more than chasing profit.

Why limit risk per trade

Losing streaks are unavoidable, even for experienced traders. If only a small share of the account is at risk on each trade, a bad run of losses is far less likely to wipe out the account.

A fixed risk limit also reduces emotional pressure. Decisions follow a plan written in advance, not fear of missing a move or the urge to win back losses quickly.

A fixed percentage also scales position size with your account. When the balance grows, the allowed risk grows; when it shrinks, the allowed risk shrinks too.

The formula

Start by defining three values:

• Risk amount = account balance × 1%.
• Risk per unit = entry price minus stop-loss price (for a long position).
• Position size = risk amount / risk per unit.

In short form: Position size = (Account × 1%) / (Entry price − Stop-loss price).

For a short position, the subtraction is reversed: the stop sits above the entry, and risk per unit is the distance between the two.

A worked example with hypothetical numbers

Suppose an account holds $10,000. The risk per trade is 1%, which equals $100. A trader plans to enter at 50 with a stop-loss at 48, so the risk per unit is $2.

Position size = $100 / $2 = 50 units. The position's value is 50 × 50 = $2,500.

If the stop is hit, the loss will be about $100, before commissions and slippage. That is 1% of the account. Now imagine the stop is placed farther away, at 45. The risk per unit becomes $5, and with the same $100 limit the position shrinks to 20 units. The wider the stop, the smaller the position for a fixed amount of risk.

Common mistakes

• Choosing position size by feel or by the entire available balance.
• Moving the stop-loss further away after entry to avoid taking a loss. This pushes the risk beyond the plan.
• Ignoring commissions, spreads, and slippage, which can make the real loss larger than calculated.
• Raising risk above 1% after a losing streak in an attempt to recover quickly.
• Setting a stop without a link to the trade's logic, only to make the position smaller.

What it means for traders

• Decide the risk amount first, then the stop level, and only then the position size.
• The stop-loss should match the logic of the trade. Position size adapts to the stop, not the other way around.
• One percent is a common benchmark for beginners, and many traders start with an even smaller figure.
• Keep a trade journal and check whether the risk limit was respected on every trade.
• A correct calculation does not guarantee profit. The rule only caps the damage from a single trade, while overall results depend on many other factors.