Position sizing

Position sizing is arguably the most important aspect of money management in forex trading. It determines how much of your capital you allocate to each trade and directly controls your risk exposure.

Understanding lot sizes

In forex, lot size defines the volume of your trade. There are three standard lot sizes:

• Standard Lot — 100,000 units of the base currency. A 1-pip move equals approximately $10.
• Mini Lot — 10,000 units. A 1-pip move equals approximately $1.
• Micro Lot — 1,000 units. A 1-pip move equals approximately $0.10.

Choosing the right lot size is critical for managing your risk per trade and preserving your trading capital.

The percent risk model

The most widely used position sizing method is the percent risk model, where you risk a fixed percentage of your account equity on each trade. A common guideline is to risk no more than 1-2% of the account per trade. It is a convention, given here as an example and not as a recommendation: it limits what a run of ordinary losses can cost, but not a loss that overshoots a stop in a gap, and it does not make a strategy profitable. The position size calculator shows the arithmetic, and the Risk Room shows what a run of losses does at different percentages.

The formula for calculating your forex position size:

Position Size = (Account Equity × Risk Percentage) / (Stop Loss in Pips × Pip Value)

For example, with a $10,000 account risking 2% with a 50-pip stop-loss: Position Size = ($10,000 × 0.02) / (50 × $10) = $200 / $500 = 0.4 standard lots (or 4 mini lots).

Fixed fractional method

The fixed fractional method is a systematic approach to position sizing where you risk a constant fraction of your current equity on every trade. As your account grows, your position sizes increase proportionally. As your account shrinks during drawdowns, your position sizes decrease, which slows the depletion of the account but does not prevent it.

Key advantages of the fixed fractional approach:

• Automatically adjusts to your current account balance.
• Compounds gains as your account grows.
• Reduces exposure during losing streaks.
• Provides consistent risk per trade in percentage terms.

The Kelly criterion

The Kelly Criterion is a mathematical formula that calculates the optimal position sizing to maximize long-term growth based on your edge:

Kelly % = W - [(1 - W) / R]

Where W is the win rate and R is the average win/loss ratio. For example, with a 55% win rate and 1.5 average win/loss ratio: Kelly % = 0.55 - (0.45 / 1.5) = 0.55 - 0.30 = 25%.

Most traders use a fraction of the full Kelly Criterion (typically half-Kelly or quarter-Kelly) to reduce volatility and the risk of large drawdowns.

Calculating lot sizes in practice

To determine the optimal lot size for each trade:

• Define your maximum risk per trade (e.g., 1% of $10,000 = $100).
• Identify your stop-loss distance in pips based on technical analysis.
• Calculate the pip value for the specific currency pair and lot size.
• Divide your dollar risk by the total pip risk to find the correct position size.
• Round down to the nearest available lot size — never round up.

Position sizing rules

Rules of thumb that are widely quoted:

• Never risk more than 2% of your account on a single trade.
• Limit total portfolio risk to 5-6% across all open positions.
• Reduce position sizes during drawdowns and losing streaks.
• Increase position sizes gradually as your account equity grows.

These are conventions, quoted here as examples and not as recommendations. Each caps the loss that is planned. The loss that happens can be larger when a stop is filled beyond its level, and positions that move together can breach a portfolio limit at the same moment.

Revised 4 October 2026. The 1-2% guideline and the widely quoted sizing rules are now described as conventions and examples, with what they do and do not protect against.