Position Size Calculator
Oversizing a single position is the fastest way to breach your daily loss limit. Pick your firm below to calculate safe position sizes based on your specific rules.
Why Position Sizing Matters More in Prop Firm Trading
Personal account traders can survive a bad position size. The loss hurts, but the account stays open. Prop firm traders do not get that luxury. One oversized trade that breaches the daily loss limit terminates the evaluation. Your $300 challenge fee is gone. You start over.
The math is unforgiving. On FTMO with a 5% daily loss limit ($5,000 on a $100K account), a single trade risking 2% of account ($2,000) with a 2:1 stop means one loss takes 40% of your daily budget. Two losses and you are at 80%. One more bad tick and the challenge is over.
Contrast this with risking 0.5% of the daily limit ($25) per trade. You can take 20 consecutive losers before breaching. That is the difference between a system that survives bad days and one that does not.
Frequently Asked Questions
How do I calculate position size for prop firm trading?
Divide your maximum risk per trade (a fraction of your daily loss limit) by your stop loss distance in pips multiplied by the pip value. For example, on a $100,000 FTMO account with a $5,000 daily loss limit, risking 1% of that limit gives you $50 risk per trade. With a 20-pip stop on EUR/USD (pip value $10/lot), your max position is 0.25 lots.
What position size should I use for a prop firm challenge?
Most successful prop firm traders risk 0.5-1% of their daily loss limit per trade. This allows 5-10 losing trades in a day before hitting the limit. Oversizing is the #1 cause of daily loss breaches. On FTMO with a 5% daily loss limit, risk $250-500 per trade on a $100K account.
Does position size change with trailing drawdown?
Yes. With trailing drawdown (TopStep, Apex), your safety buffer shrinks as the floor rises with equity peaks. After a winning streak, reduce position size because your distance to breach is smaller. With static drawdown (FTMO), profits add buffer, so your effective risk tolerance increases.
What is the 1% rule in prop firm trading?
The 1% rule means risking no more than 1% of your account balance per trade. In prop firm trading, it is better to apply 1% to your daily loss limit, not the full account. On a $50K TopStep account with a $1,000 daily loss limit, risk $10 per trade -- far less than 1% of $50K ($500).