Most traders spend their energy on entries: the pattern, the indicator, the perfect level. Yet the decision that most determines whether an account survives its first year is far less glamorous: how much to risk on each trade. This article explains fixed-fractional position sizing, why it works, and the arithmetic of losing streaks that makes it non-negotiable.
Risk is decided before the trade, not during it
Every trade has three numbers you can set in advance:
- Entry: where you get in.
- Invalidation: the price at which your idea is clearly wrong, which is where the stop-loss belongs.
- Size: how many units you trade.
The market decides whether you are right. You decide how much it costs you to be wrong. The common mistake is to choose size first ("I always trade one lot") and then squeeze the stop to fit. That puts the stop at a price that means nothing to the market, and you get stopped out by ordinary noise. The better order is: find the logical invalidation level, measure the distance, then calculate the size that keeps the loss within budget.
The fixed-fractional method
Fixed-fractional sizing means risking the same small percentage of current account equity on every trade. Many self-directed traders use somewhere between 0.5% and 2%; 1% is a common reference point. The formula is:
Position size (units) = (Account equity x Risk %) / (Stop distance in pips x Pip value per unit)
Illustrative example:
- Account equity: $10,000
- Risk per trade: 1% = $100
- Pair: EUR/USD in a USD account, so pip value is $1 per 10,000 units (a mini lot)
- Logical stop: 40 pips from entry
Size = $100 / (40 pips x $1 per mini lot) = 2.5 mini lots = 25,000 units. If the stop is hit, the loss is about $100 plus spread and any slippage.
Now suppose a different setup needs a 100-pip stop. Same budget: $100 / (100 x $1) = 1 mini lot. The wider stop gets a smaller position, so the dollar risk stays constant. That is the whole point: every trade costs the same if wrong, regardless of how far away the stop is.
For pairs where your account currency is not the quote currency (for example USD/JPY in a CAD account), the pip value per unit must be converted. Our pip value guide covers the idea, and the position-size calculator on the 24hrfx homepage does the arithmetic for you. If the relationship between lots and exposure is still fuzzy, read lots, leverage and margin first.
The arithmetic of losing streaks
Here is why the percentage matters so much. Even a sound approach with a 50% win rate will produce long losing streaks. Over a few hundred trades, a run of six, seven or eight losers in a row is not unusual bad luck; it is expected. What that streak does to your account depends entirely on risk per trade.
| Risk per trade | Account after 10 straight losses | Gain needed to get back to start |
|---|---|---|
| 0.5% | -4.9% | +5.1% |
| 1% | -9.6% | +10.6% |
| 2% | -18.3% | +22.4% |
| 5% | -40.1% | +67.0% |
| 10% | -65.1% | +186.8% |
(Figures assume risk is recalculated on remaining equity after each loss. Illustrative.)
At 1%, ten straight losses hurt but leave you very much in the game. At 10%, the same streak leaves you needing to nearly triple what is left just to get back to even. The trading method is identical in both rows; only the sizing differs. This asymmetry, where losses require ever-larger gains to recover, is the single most important piece of arithmetic in trading.
Why fixed-fractional is self-correcting
Because you risk a percentage of current equity, your position size shrinks automatically during drawdowns and grows during winning periods. After losing 10% of a $10,000 account, 1% risk is $90 rather than $100. That built-in brake slows the damage when things are going badly, which is exactly when traders are most tempted to do the opposite and "size up to win it back".
Add a portfolio-level cap
Per-trade risk is not the whole story. Five open trades at 1% each is 5% at risk, and if they are all correlated (say long EUR/USD, GBP/USD, AUD/USD and NZD/USD, and short USD/CHF) they are effectively one large bet against the US dollar. Useful extra limits include:
- Maximum total open risk, for example 3% to 5% of equity across all positions.
- Maximum risk per currency, so you cannot accidentally stack the same exposure through several pairs.
- A daily loss limit, after which you stop trading for the day. It protects you from the emotional spiral that can follow a bad morning.
What the stop-loss does and does not guarantee
A stop-loss order caps your planned loss under normal conditions. It does not guarantee the fill price. Around major data releases, central-bank decisions and the weekly open, price can jump past your stop and you will be filled at the next available price. Two practical habits help:
- Know the calendar. If a major release is due while you are in a trade, either reduce size or accept that the realized loss could exceed plan. Our article on how central-bank decisions move FX explains why these events cause gaps.
- Budget for slippage. Some traders size for 1% but treat 1.2% to 1.5% as a realistic worst case on an eventful day.
Common sizing mistakes
- Using the same lot size for every trade regardless of stop distance. Your risk then varies wildly from trade to trade.
- Moving the stop further away once the trade goes against you. That silently increases the risk you already committed to.
- Raising risk after a loss to recover faster. The losing-streak table shows where that leads.
- Ignoring costs. On short-term trades with tight stops, the spread can be a meaningful fraction of the stop distance.
Bottom line
Position sizing will not make a bad approach profitable. What it does is keep you in the game long enough to find out whether your approach works, and to improve it. Pick a small, fixed percentage; calculate size from a logical stop on every trade; cap total exposure; and never let a losing streak talk you into breaking the rule.
This article is general education, not investment advice. Leveraged FX trading carries a high risk of loss. All examples are illustrative.