Ask ten profitable traders what separates them from losing traders and most won't mention entries. They'll mention position sizing. You can have a mediocre strategy with disciplined sizing and survive; you cannot have a brilliant strategy with reckless sizing and survive a losing streak.
The Core Formula
Position size is derived backward from three inputs: how much money you're willing to lose (risk amount), how far your stop is from entry (stop distance), and what one pip/point is worth at a given size (pip value). You never decide position size first and hope the loss is acceptable — you decide the acceptable loss first.
Risk Amount ($) = Account Equity × Risk % per TradePosition Size (lots) = Risk Amount ($) / (Stop Distance in Pips × Pip Value per Lot)Worked Example
Account: $10,000. Risk per trade: 1%. Risk amount = $100. Entry on EUR/USD at 1.0850, stop at 1.0800 = 50 pips distance. For a standard lot (100k units) on EUR/USD, one pip ≈ $10. So position size = $100 / (50 × $10) = 0.2 lots.
| Account Equity | Risk % | Stop (pips) | Position Size |
|---|---|---|---|
| $5,000 | 1% | 20 | 0.25 lots |
| $10,000 | 1% | 50 | 0.20 lots |
| $25,000 | 0.5% | 30 | 0.42 lots |
| $50,000 | 1% | 15 | 3.33 lots |
Why 1-2% Is the Standard Range
Risking 1-2% per trade means a losing streak of 10 trades costs you roughly 10-20% of equity — painful but recoverable. Risking 5% per trade, the same streak wipes out 40%+ of the account because losses compound against a shrinking base. Professional risk managers rarely allow more than 2% on a single idea.
The amount of margin your broker lets you use has nothing to do with sound risk. Brokers offer 1:500 leverage; that doesn't mean you should use it. Size from your stop distance and risk %, never from 'how big a position can I open'.
Adjusting for Volatile Pairs
A 50-pip stop on EUR/USD and a 50-pip stop on GBP/JPY are not the same risk in practice, because pip value and typical range differ. Always run the formula per instrument rather than using a fixed lot size across all pairs.
Common Sizing Mistakes
- ▸Sizing up after a loss to 'win it back' — this is martingale thinking and destroys accounts.
- ▸Widening the stop after entry instead of accepting the loss — turns a 1% risk into 3-4%.
- ▸Ignoring correlation — three 1% trades on correlated pairs is really one 3% trade.
- ▸Using a fixed lot size regardless of stop distance — a tight stop and wide stop should never carry the same position size.
Build or use a position size calculator that takes account size, risk %, and stop distance as inputs. Removing manual math removes an entire category of costly errors under pressure.