Take two traders who enter ES at the same price with the same 10-point stop. One trades 1 contract on a $10,000 account and the other trades 5. If both stops hit, the first loses $500 (5% of the account) and the second loses $2,500 (25%). The analysis was identical. The only difference was size, and size is what decides whether the next trade gets taken calmly or in a hole. These numbers are hypothetical.
Start with dollars at risk
The question that sets size is how much you'll lose if the trade is wrong. Pick a fixed dollar amount, or a fixed percentage of the account, and hold it constant regardless of how confident you feel. Common conventions are 0.5%, 1% and 2% per trade. They are conventions, not guarantees, and 2% is a lot for anyone who hasn't survived a long losing streak. On a $25,000 account, 1% is $250.
The formula
Your next step
Check the math before you size up.
Use your recorded win rate, average win and loss, and trading costs in the free edge calculator. Estimates are a starting point, not proof of an edge.
Contracts = risk per trade in dollars, divided by (stop distance in points times point value), rounded down. Never round up, because rounding up is how a 1% rule becomes a 1.6% rule without anyone deciding it.
Example 1: ES versus MES on $25,000
Risk is $250 and the planned stop is 8 points. One ES at $50 a point risks $400 per contract, so $250 divided by $400 is 0.625. You can't trade 0.625 of a contract, and 1 ES risks $400, or 1.6% of the account. Switch to MES at $5 a point: 8 points is $40 per contract, and $250 divided by $40 is 6.25, so 6 MES risk $240.
Example 2: MNQ on $10,000
Risk at 1% is $100. A 25-point stop on MNQ at $2 a point is $50 per contract, so $100 divided by $50 gives 2 MNQ. Micros exist so smaller accounts can size close to their target risk.
Example 3: a daily loss limit
Hypothetically, say a simulated evaluation account has a $2,000 max loss limit. Risking $500 per trade, three losers in a row use $1,500, or 75% of the limit, before commissions and slippage. At $250 per trade the same sequence uses $750. Read the rule document carefully, because a trailing limit can leave you with less cushion than the starting number suggests. A three-loss daily cap is a simple way to turn a per-trade rule into a daily one.
Tick and point values
| Contract | Tick size | Value per tick | Value per point |
|---|---|---|---|
| ES | 0.25 | $12.50 | $50 |
| MES | 0.25 | $1.25 | $5 |
| NQ | 0.25 | $5.00 | $20 |
| MNQ | 0.25 | $0.50 | $2 |
| YM | 1 point | $5 | $5 |
| RTY | 0.10 | $5 | $50 |
| CL | 0.01 | $10 | $1,000 |
| GC | 0.10 | $10 | $100 |
What the formula doesn't cover
It assumes you exit at your stop. Stop orders can slip, especially around scheduled news, so the real loss can exceed the planned loss. Leave room for that, and don't treat margin as a loss limit either. Margin is collateral, and a position can lose more than the margin posted. Commissions and fees also come off every trade, so on tight stops they take a meaningful share of the risk budget.
Sizing mistakes I see most
Sizing from the target
Picking size because you want to make $500 today is backwards. Size from what you can afford to lose, then let the target follow from the setup.
Ignoring stop width
A 4-tick ES stop with 3 contracts risks 4 x $12.50 x 3 = $150. A 20-tick stop with the same 3 contracts risks $750. Same contracts, five times the risk. Contracts must shrink as the stop widens.
Averaging down
Adding to a loser raises your risk after the trade has already told you something. If you want to scale in, define the whole position and its total risk before the first fill.
Size that varies with mood
Going bigger on trades you feel good about makes results hard to evaluate, because your biggest losses land on the trades you were most sure about. Flat risk keeps the record readable.
A stale risk number
If 1% was calculated on the starting balance and the account has grown or shrunk, recompute it. Monthly is a reasonable minimum.
If you run automation
With an automated strategy, size is a configuration setting instead of a moment-to-moment choice, which makes it easy to forget about. Pro includes bot access, and the current parameters for each bot are in the Marty bot specs and the KPL bot specs. Check any prop firm's automation rules before using a bot on that firm's account. Apex, for example, prohibits automated or algorithmic preset bots that place, modify or cancel trades without personal real-time review; see the Apex prohibited activities page and the user agreement.
Why fixed risk helps with discipline
When the maximum loss on a trade is a number you chose in advance, you have less reason to move a stop or hold a loser and hope. That's a process benefit, not a profit claim. Sizing doesn't create an edge. It only limits what a stretch of bad trades can do while you find out whether you have one. For the follow-on topic of stops, see risk management for automated trading.
About the Author
Founder, Young Money Investments · Quant Trader
Cameron trades ES, NQ, and futures across multiple market cycles. He founded Young Money Investments to teach systematic, data-driven trading and manages Magnum Opus Capital. His work emphasizes documented rules, risk controls, and review over outcome promises.
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