How to calculate position size so you do not lose more than 1%?
Part 1 of 3The 1% rule — why it matters
The 1% rule says you risk no more than 1% of capital on any single trade. For a $10,000 account that's $100 of risk per trade — regardless of how "certain" the setup looks.
Why 1%? Because statistically every strategy produces losing streaks — sometimes 5, sometimes 10, sometimes 15 losses in a row. With 1% risk, 10 losses in a row take ~10% of capital (geometrically 9.6%). With 5% risk — ~40%. With 10% — ~65%, and accounts rarely recover to break-even.
Part 2 of 3The position-size formula
Three variables are enough:
- Capital × 1% = max loss in account currency
- SL distance in pips = how many pips from entry to stop loss
- Pip value for the pair and lot
Formula: Position size in lots = (Capital × 1%) / (SL distance × pip value per 1 lot)
Part 3 of 3Example: EUR/USD, $10,000 account, 30-pip SL
You open 0.33 lot, not 1 lot. If SL hits — you lose $100, i.e. 1% of capital. Your account survives a 10-loss streak with minimal damage.
Sources & bibliography
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Van K. Tharp Institute About Van K. Tharp — pioneer of position sizing · Author biography & methodology www.vantharp.com ↗
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Van K. Tharp / McGraw-Hill Trade Your Way to Financial Freedom (1999), Position Sizing chapter · ISBN 978-0-07-147871-7 www.mhprofessional.com ↗
Frequently asked
Does the 1% rule work on a small account, e.g. 500 USD?
Yes, but it requires micro lots. With a 500 USD account the 1% rule means a maximum of 5 USD risk per trade. With a 30-pip stop loss and a pip value of 0.10 USD on a micro lot (0.01 lot), the maximum position size is about 0.017 lot, roughly 1.7 micro lots. Most ECN brokers allow positions as small as 0.01 lot, so the rule is executable. Accounts below 500 USD heavily restrict available instruments and sometimes make 1% too small to cover typical spreads.
Should I risk more than 1% on a very good setup?
Subjective assessment of how "certain" a setup looks is one of the main psychological traps in trading. Research on decision-making under uncertainty (Kahneman, Tversky) shows that people systematically overestimate the probability of events they are focused on. Even a strategy with 65% win rate still loses on 35 of every 100 trades — and those losses do not spread evenly over time. Increasing risk above 2% requires a documented, multi-month edge in a live account. In any other situation the 1% rule protects against emotions influencing position size.
How do I convert pip value when my account is in EUR but I trade USD/JPY?
For USD/JPY one pip is 0.01, and the pip value per standard lot in dollars depends on the current USD/JPY rate — at 150.00 it is roughly 6.67 USD. To convert to EUR, divide the dollar value by the EUR/USD rate. With EUR/USD at 1.09, one pip on a standard USD/JPY lot equals about 6.67 / 1.09 = ~6.12 EUR. Most platforms calculate this conversion automatically and display the pip value in the account currency. It is worth checking it in the position calculator before opening any JPY-pair trade.