Position size = (Account size × risk %) ÷ (Entry price − Stop price). This ensures every trade risks the same R, whether your stop is tight or wide. Most traders memorize this formula wrong or apply it inconsistently, which is why position sizing is the #1 thing that kills accounts.
- Formula is fixed; your entry and stop are flexible
- Sizing wrong is worse than picking wrong setups
- If the calculated size seems too small, the setup's risk is too high or your edge isn't there yet
- Adjust your entry/stop to get to a sensible size; don't fudge the numbers
Most traders can't even state the position sizing formula from memory. That's why they blow up.
The formula
Position size = (Account size × Risk %) ÷ (Entry price − Stop price)
This formula works for stocks, options, futures, and forex. Everything.
Walking through an example
Setup: Opening range breakout on $AAPL
Your numbers:
- Account: $25,000
- Risk per trade: 1% = $250
- Entry: $150.00
- Stop: $148.50 (you define this before entry)
Calculation:
- Stop risk: $150.00 − $148.50 = $1.50 per share
- Position size: $250 ÷ $1.50 = 166.67 shares
- Round to 166 shares (your broker won't let you buy 0.67)
Verify:
- 166 shares × $1.50 risk = $249 total risk (close to $250 ✅)
Target: $153.50 (3.50 gain ÷ 1.50 risk = 2.33R target)
Outcome:
- If stop hits: −$249 (exactly 1% of $25K) ✅
- If target hits: +$581 (+2.33R) ✅
Know Your Real Risk on Every Trade
TRADZY tracks R-multiples, drawdown and daily loss automatically, so your rules hold when it matters.
Track Risk in TRADZY →The three most common mistakes
Mistake 1: Using the formula backward
❌ Wrong: Position size = (Entry − Stop) × Account size
This multiplies your risk, not divides it.
✅ Right: Position size = (Account × Risk %) ÷ (Entry − Stop)
Mistake 2: Forgetting to convert percentage to dollars
❌ Wrong: "I'll risk 1 position." (Meaningless)
❌ Wrong: "I'll risk $25,000 × 1% = 1% of the account as risk" (You didn't do the math)
✅ Right: "I'll risk 1% = $250 per trade."
Mistake 3: Adjusting size based on how you feel
❌ "This setup looks really good, so I'll size up to 2%." ❌ "I'm down money, so I'll size down to 0.5%."
✅ Position size comes from math, not emotion. 1% every time.
Different scenarios
Scenario 1: Tight stop, small position
| Entry | Stop | Risk | Account | Size |
|---|---|---|---|---|
| $150 | $149.50 | $0.50 | $10,000 (1%) | $100 ÷ $0.50 = 200 shares |
Tight stop = bigger position (at same risk %). Good. Tight stop = high conviction.
Scenario 2: Wide stop, small position
| Entry | Stop | Risk | Account | Size |
|---|---|---|---|---|
| $150 | $145 | $5.00 | $10,000 (1%) | $100 ÷ $5.00 = 20 shares |
Wide stop = tiny position (at same risk %). This tells you something: your setup doesn't have conviction. The risk is too high relative to the move you expect.
Action: Adjust your entry/stop to tighten the risk. If you can't, skip the trade.
Scenario 3: Options (debit spread)
| Strategy | Debit | Account | Size |
|---|---|---|---|
| Bull call spread, $3.20 debit | $3.20 max loss per contract | $20,000 (1%) | $200 ÷ $3.20 = 62 contracts |
Options work the same way: max loss per contract acts as the "stop."
The wrong way (how most traders actually do it)
- Decide "I want to buy 100 shares."
- Set a random stop ("somewhere under $150").
- Calculate risk: 100 × stop = uncertainty.
- Hope it works out.
Result: Inconsistent risk. Some trades risk $50, some risk $300, on the same $10K account. You don't know your actual expectancy because position sizes are all over the place.
The right way (mechanical)
- Choose entry based on setup.
- Choose stop based on where you're wrong (technical level just below entry).
- Calculate: Risk per share = Entry − Stop
- Calculate: Position size = ($10,000 × 1%) ÷ Risk per share
- Execute that exact size. No rounding, no exceptions.
When position size gets weird
If your formula gives you a fractional share, you have a choice:
Option 1: Accept fractional shares. Most brokers allow this now. Means exact 1% risk.
Option 2: Adjust your stop by 1 tick to get a round number.
- Formula gives 166.67 shares
- Adjust stop to $148.49 instead of $148.50
- New calculation: $250 ÷ $1.51 = 165.56 → 165 shares
- Risk is now $248.75 (close to 1%)
Option 3: Reduce your risk % slightly to get a round number.
- Formula gives 166.67 shares
- Use 166 shares instead
- Risk = 166 × $1.50 = $249 (close to $250)
All three are acceptable. Never round up (that's risk above 1%).
Position sizing for different instruments
Stocks: price per share
| Entry | Stop | Risk per share |
|---|---|---|
| $150 | $149 | $1 |
| $50 | $48 | $2 |
| $250 | $245 | $5 |
Formula: (Account × 1%) ÷ risk per share = number of shares
Futures: points per contract
| Entry | Stop | Risk per point | Points risked | $/contract risk |
|---|---|---|---|---|
| 6,050 | 6,000 | 50 points | 50 | 50 × $50 = $2,500 |
On a $50,000 account (1% = $500): You can't take this trade with 1% risk. Stop is too wide. Adjust it.
Options: debit per contract
| Strategy | Max loss per contract | Account 1% | Contracts |
|---|---|---|---|
| Bull call spread | $320 | $500 | $500 ÷ $320 = 1.56 contracts |
Round to 1 contract. Risk = $320 (3.2% if account is $10K; use a bigger account or tighter risk).
Forex: pips per contract
| Pair | Entry | Stop (pips) | Risk per pip |
|---|---|---|---|
| EUR/USD | 1.0950 | 30 pips | $1/pip per mini lot |
1 mini lot = $1/pip. 30 pips risk = $30 per mini lot.
On $10,000 account (1% = $100): $100 ÷ $30 = 3.33 mini lots → 3 mini lots.
The master rule
Your position size should make you indifferent to the outcome of a single trade.
- +1R: "OK, moving on."
- −1R: "OK, moving on."
If you feel relief or dread at a 1% loss, you're sizing too big or your account is too small. Either:
- Reduce position size (use 0.5% risk per trade instead of 1%)
- Grow your account
- Use a simulator until you're comfortable
FAQ
Should I round up to get a bigger position?
No. Ever. Rounding up breaks the formula and magnifies risk.
Can I use different risk percentages on different setups?
No, not until you're consistently profitable. Consistent 1% per trade is the discipline foundation. After 500+ profitable trades, you might risk 0.5% on low-conviction and 1.5% on high-conviction. But track everything religiously.
What if my position size ends up being 1 share?
That's fine. It means your account is small relative to your stop width. You're risking the full 1%, but only 1 share. Options: Paper trade, grow your account, or reduce your risk % to 0.25%.
Does position sizing guarantee profit?
No. It ensures you survive. Profitability comes from edge (positive expectancy). Position sizing just lets you live long enough to prove the edge.
What happens if I size up when I'm winning?
Your average risk goes up. You're violating the 1% rule. Your actual expectancy is lower than you think. If you want to scale, grow your account size first. If you have $10K and it becomes $11K, your 1% risk goes from $100 to $110 automatically. That's scaling. Everything else is gambling.
Put This Into Practice
- Set your risk per trade and daily loss limit once
- Track every trade in R, not dollars
- Watch drawdown and expectancy update automatically
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Educational content, not financial advice. Trading involves substantial risk of loss.