Updated 29 September 2026
What the 80% margin rule means
Some prop firms limit how much margin your open trades may use at any moment, commonly 80% of the account. If one trade, or all your trades together, lock up more than that, the firm can count it as a rule breach. Traders often find out only when a payout is reviewed and refused, even though the account was in profit.
Margin used % = Total margin of open trades ÷ Balance (or equity) × 100
On a $10,000 account with an 80% rule, your open trades may lock up at most $8,000 of margin. The calculator above adds up every open trade and the new one, then tells you whether you stay under that line.
How to use the calculator
- Pick the instrument and check the price. Choose the leverage your funded account has on that symbol.
- Enter the lot size you want to open and your account balance.
- Choose whether your firm measures the rule on balance or equity, and set the limit (80% by default).
- Add any trades that are already open, or type the Margin figure from MT5.
- Optional: add your risk and stop loss for a suggested lot size, and your daily loss limit.
- Press Calculate. SAFE in green means total margin stays under the limit. BREACH in red means it goes over, and the calculator shows the lot size that fits.
Max lot size cheat sheet
The biggest single trade that stays under an 80% margin limit with no other trades open, rounded down to 0.01 lot. Prices move, so use the calculator for the exact figure right now.
| Account | 1:10 | 1:30 | 1:100 |
|---|---|---|---|
| $5,000 | 0.09 | 0.28 | 0.96 |
| $10,000 | 0.19 | 0.57 | 1.92 |
| $25,000 | 0.48 | 1.44 | 4.81 |
| $50,000 | 0.96 | 2.89 | 9.63 |
| $100,000 | 1.92 | 5.78 | 19.27 |
| Account | 1:10 | 1:30 | 1:100 |
|---|---|---|---|
| $5,000 | 0.35 | 1.05 | 3.50 |
| $10,000 | 0.70 | 2.10 | 7.01 |
| $25,000 | 1.75 | 5.26 | 17.54 |
| $50,000 | 3.50 | 10.52 | 35.08 |
| $100,000 | 7.01 | 21.05 | 70.17 |
| Account | 1:10 | 1:30 | 1:100 |
|---|---|---|---|
| $5,000 | 1.30 | 3.92 | 13.07 |
| $10,000 | 2.61 | 7.84 | 26.14 |
| $25,000 | 6.53 | 19.60 | 65.35 |
| $50,000 | 13.07 | 39.21 | 130.71 |
| $100,000 | 26.14 | 78.43 | 261.43 |
Why traders break the rule after passing
Many firms give lower leverage on funded accounts than in the challenge, and lower leverage on gold and indices than on currency pairs. Margin rises in the same proportion: a trade that used 8% of the account at 1:100 uses 80% at 1:10. On a $5,000 account, one lot of gold at 4,150 needs about $4,150 of margin at 1:100, which is already 83% of the account. At 1:10 the same trade needs $41,500.
Worked example: $5,000 funded account at 1:10
80% of $5,000 is $4,000 of margin. Risk is 1% ($50) per trade.
| Trade | Margin rule | 1% risk | Lot to trade | Margin used |
|---|---|---|---|---|
| XAUUSD at 4,150, $8 stop | 0.09 | 0.06 | 0.06 | 49.8% |
| XAUUSD at 4,150, $3 stop | 0.09 | 0.16 | 0.09 | 74.7% |
| EURUSD at 1.1400, 20-pip stop | 0.35 | 0.25 | 0.25 | 57.0% |
| NAS100 at 30,600, 50-point stop | 1.30 | 1.00 | 1.00 | 61.2% |
In the second row a tight stop lets your risk allow 0.16 lots, but that would need more than $4,000 of margin. The margin rule wins and caps the trade at 0.09.
Balance or equity?
Firms word the rule differently. Some compare margin with your balance, others with your equity, which includes open profit and loss. When you are in a losing trade, equity is lower than balance, so the same margin is a bigger share of it. If your firm uses equity, choose Equity in the calculator and type the equity figure from your platform.
When you already have trades open
The rule looks at all open positions together. List each open trade with its lots and leverage, or type the total Margin figure from your platform. With 0.06 lots of gold already open on a $5,000 account at 1:10 ($2,490 of margin), the most EURUSD you can add is 0.13 lots.
Margin rule and daily loss limit
These are two separate rules. The margin rule is about how much of the account your open trades lock up. The daily loss limit, often 5% of the day's starting balance, is about how much you can lose in one day. A trade can pass one and break the other, so the calculator checks both: margin for the lot size, and your stop loss against the daily room left.
Where to see margin in MT5 and cTrader
- MT5: open the Toolbox (Ctrl+T) and the Trade tab. The top line shows Balance, Equity, Margin, Free margin and Margin level.
- MT5 on phone: the Trade screen shows the same figures above your open positions.
- cTrader: the Trade Watch panel at the bottom shows Balance, Equity, Margin and Free margin.
Margin used % is Margin ÷ Balance (or Equity) × 100. Keep it below your firm's limit at all times, not only when you open a trade.
Mistakes that lead to a breach
- Keeping the same lot size after moving from the challenge to a funded account with lower leverage.
- Adding a second trade without counting the margin of the first.
- Opening several small trades on gold that add up to more than the limit.
- Opening right at the limit, then watching margin rise as price moves.
- Assuming the rule uses balance when the firm measures equity.