Ask an experienced trader which number on a trade sheet matters most and the answer is rarely the entry price. It is the lot size, because that single figure decides whether a stopped-out trade is a routine deduction or a hole you spend months climbing out of. Position size is the variable you actually control, and it can be calculated before the market does anything at all.
Exposure is not risk
The two get confused constantly. A 0.50 lot position is the same exposure whether the stop is twenty pips or two hundred, but the risk is ten times different. The balance tells you how much a market move costs; the stop tells you how far you have agreed to be wrong. Risk is the product of the two, and only the product is meaningful.
So the sequence is not "how much can I buy" but "how much do I intend to lose if this trade is wrong", and then the lot size falls out of the arithmetic.
The four steps
The following is an illustration with round numbers, not a template for any account. Use your own balance and your own broker's contract specifications.
- Fix the money at risk. For example, a notional account of one thousand dollars with a self-imposed limit of one percent per trade gives ten dollars of risk on this position. The percentage is arbitrary and personal; the requirement is that it be decided before the trade rather than during it.
- Measure the stop distance. Say the structure of the market puts the logical stop twenty-five pips away. That figure comes from the chart, not from the account balance. A stop that is only there because it suits the risk budget is not a stop; it is a hope with a number attached.
- Derive the affordable pip value. Ten dollars of risk divided by twenty-five pips gives forty cents per pip. This is the step most people skip, and it is the one that makes sizing possible.
- Convert to lots. On a four-digit pair quoted in dollars, one micro lot of one thousand units is worth roughly ten cents per pip. Forty cents therefore means roughly four micro lots, or 0.04 lots.
Change the stop to fifty pips on the same account and the size halves to about 0.02. Nothing about the trade idea changed, but the risk per trade stayed fixed. That is the entire point of the method: the account loses the same amount per mistake however wide the mistake is, and a strategy can therefore be assessed without the results being dominated by sizing luck.
Where the arithmetic breaks
Four places deserve checking every time rather than once.
- Yen pairs. A pip is 0.01, and pip value is denominated in yen, so it converts into the account currency at a moving rate.
- Gold and indices. Contract sizes and point conventions differ between platforms. Derive the figure from the specification, never from a rule of thumb formed on currency pairs.
- Account currency. If it is neither the base nor the quote currency, every pip value carries a second conversion.
- Costs outside the formula. Spread, commission and swap are not in the risk number but are paid in the same account. A tight stop with a wide spread is a different trade from a tight stop with a tight one.
The failure this prevents
The common route to a blown account is not a single catastrophic trade. It is a series of positions sized to feel meaningful rather than to a defined risk, followed by one ordinary losing streak that is larger than the sizing assumed. Ten consecutive losses at one percent per trade is a manageable drawdown; at five percent with the stop widened to make the trade feel comfortable, it is close to an unrecoverable one.
Losing streaks happen to every approach that trades at all, including ones with sound logic. Sizing is not about preventing them. It is about surviving them while you decide whether the approach still deserves your money, which is a far calmer question to answer at ten percent down than at sixty.
Risk disclosure
The figures above are illustrative and use a hypothetical account for arithmetic only. They are not a recommendation of any risk level. Leveraged trading can produce losses greater than deposits, and no sizing method makes a strategy profitable or a loss recoverable by right. This is education, not financial advice, and you should trade only capital you can afford to lose.