Position Size
Calculator.
Work out the lot size that respects your own risk rule and your prop firm rules at the same time. The calculator names which of the three limits is actually binding your trade.
This is set from the instrument above and stays editable. It is not pulled from a live price feed, so for JPY pairs and anything exotic, check the pip value in your own platform before you rely on it.
You will get the size that respects all three.
Why risk percent is not the only limit
Most position size calculators ask for your account size, your risk percent and your stop, then hand back a lot size. On a personal account that is the whole answer. On a prop firm account it is not, because two firm rules sit on top of your own risk rule and either one can end the account before your risk plan ever plays out.
Your risk per trade is a choice. It decides how much a single loss costs you.
The daily loss limit is a hard rule. Cross it and most firms close the account the same day, no warning and no appeal.
The maximum drawdown is the floor for the life of the account. Touch it and the account is gone regardless of how well the rest of the month went.
This calculator works out the size allowed by each of those three limits separately, then shows you the smallest of the three and names it. That smallest number is the one that actually governs your trade. Knowing which of the three is binding tells you what to change: your stop, your risk, or the account size you bought.
How the calculation works
Each limit is converted into a dollar figure, then divided by the cash value of your stop loss:
Risk in dollars = account size multiplied by risk percent
Stop loss value per lot = stop in pips multiplied by the pip value per lot
Lots allowed = risk in dollars divided by stop loss value per lot
The same division is run against the daily loss limit and the maximum drawdown. Because the daily and maximum limits are firm rules rather than preferences, the recommended size is never allowed to exceed them, even if your own risk percent would permit a larger trade.
A worked example
Take a $100,000 account with a 5 percent daily loss limit, a 10 percent maximum drawdown, a 1 percent risk rule, a 20 pip stop and a pip value of $10 per standard lot.
Your risk rule allows $1,000, which is 5.00 lots.
The daily loss limit allows $5,000, which is 25.00 lots.
The maximum drawdown allows $10,000, which is 50.00 lots.
Your own risk rule binds, so the size is 5.00 lots.
Now widen the stop to 200 pips and keep everything else the same. Your risk rule allows 0.50 lots, the daily limit allows 2.50 lots, and the maximum drawdown allows 5.00 lots. Your risk rule still binds, and that is the healthy arrangement: your own rule should be the tightest of the three. When a firm rule binds instead, the trade is too large for the account you are on.
Consecutive losses are where accounts actually die
A single trade sized at 1 percent looks harmless against a 5 percent daily limit. Five of them in one session does not. The calculator shows how many losses at your chosen size it takes to reach the daily limit and to reach the maximum drawdown, because that number is the real constraint on how often you can be wrong in a row.
If your risk per trade divides into the daily limit fewer than three times, you are one bad session from a breach. Traders who fail evaluations usually do it here rather than on a single oversized trade.
Drawdown type changes the answer
This tool treats the maximum drawdown as a fixed percentage of your starting balance, which is how static drawdown works. If your firm uses a trailing drawdown the floor moves up as your balance grows, so your real distance to the floor is smaller than the starting percentage once you are in profit. Work out that distance first with our drawdown calculator, then come back and enter the remaining room as your maximum drawdown percentage.
Two more rules interact with position sizing and neither is captured here. A consistency rule caps how much of your total profit any single day may represent, which limits size on your best days. Some firms also cap lots per position or per symbol outright. Check both on the firm review page before sizing up.