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What it says
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Next: size the trade against the stop
The simulator assumes a fixed risk per trade. The position size calculator turns that percent into units for your stop.
What is included
- The calculator, with your own numbers
- The formula written out
- A worked example you can reproduce
- Where grid, martingale and DCA bots break the maths
Who it is for
- People running or testing a trading bot
- Anyone sizing a position or checking costs
- Readers learning how the numbers work
- Not advice, and not for placing trades
Key facts
- A prop firm challenge sets a profit target, a daily loss limit, a total loss limit and often a time limit. Reaching a limit first ends the attempt.
- This tool plays 2,000 attempts with a fixed seed, so the same inputs always give the same answer.
- Model: every trade risks the same percent of the starting balance. A win adds risk x payoff ratio and a loss takes away the risk. Trades are independent.
- Rules differ by firm and change over time: how the daily limit is measured, whether the total limit trails, and the days allowed. Enter the rules of your own challenge.
- The tile "attempts per pass" is 1 divided by the pass rate. It is a count of fees, not a promise of any result.
- Example numbers on this page are made up. A good result here says nothing certain about a real bot.
How the prop firm challenge simulator works
A prop firm challenge is a test. You trade a simulated account with three rules: reach a profit target, never lose more than the daily limit in one day, and never lose more than the total limit overall. Many also give a number of days. The first thing that happens ends the attempt: the target is a pass, a limit is a fail, and running out of days is a fail with no loss.
The simulator plays that test 2,000 times with a seeded random number generator (mulberry32, seed 987654321), so the answer is the same on every run and in every browser. On each trade the strategy wins with the chance you set. A win adds risk x payoff ratio to the result and a loss takes away risk. After every trade it checks the total limit, then the daily limit, then the target.
Loss: result = result - risk
Fail (total) if result is at or below minus the total limit
Fail (daily) if result today is at or below minus the daily limit
Pass if result reaches the profit target
A worked example
Take a made-up strategy that wins 45 percent of trades with a payoff of 1.5, so the average trade is 0.45 x 1.5 - 0.55 = 0.125 times the amount risked. Risking 1 percent of the start, two trades a day, a 10 percent target, a 5 percent daily limit, a 10 percent total limit and 30 days, 55.6 percent of the 2,000 attempts passed, 9.7 percent hit the total limit, 0.0 percent hit the daily limit and 34.8 percent ran out of days.
Now change only the size. At 0.5 percent risk 16.4 percent pass and 83.3 percent run out of days. At 2 percent 69.0 percent pass but 28.8 percent hit the total limit. At 3 percent 34.9 percent pass and 65.0 percent fail on a limit. The odds did not change. Larger size buys speed and pays for it in limit failures.
How a bot meets a challenge
- A bot that trades often can hit the daily limit. With a made-up 2 percent risk and six trades a day, 56.5 percent of attempts ended on the daily limit, against 0.0 percent at two trades a day.
- A martingale or grid bot does not fit the model. It wins often and loses rarely and large, and its size depends on earlier results. One big loss can break a daily or total limit at once. Test it with the martingale calculator and read the guide on drawdown.
- Open trades can count. Some rules measure the limit on equity, including open losses, not only on closed trades. This model checks after every closed trade, so it can miss a limit that an open trade would have hit.
- Costs are in only if you put them in. Enter a win rate and payoff that are net of spread, commission and slippage.
What the model cannot tell you
It cannot tell you that your odds are real. If a win rate comes from a backtest, overfitting may have inflated it. It also cannot tell you the rules of any firm, which differ and change. Use it to ask how sensitive a pass is to size and limits, and to see the cost in fees of a low pass rate. For the chance of any account touching a floor, use the risk of ruin calculator.
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FAQ
Frequently Asked Questions
What does the simulator assume?
Independent trades, a fixed win rate and payoff, and the same risk on every trade measured on the starting balance. Real trades cluster and odds drift, so treat the result as a sensitivity check.
Why does a larger risk raise the pass rate?
Each trade moves the result further, so the target is reached sooner and fewer attempts run out of days. The same size also moves the result towards the loss limits, which is why failures rise.
Why is the maximum 120 days?
The simulation runs in your browser. 2,000 attempts of up to 120 days and 50 trades a day stay fast on most devices.
Does it use the rules of a particular firm?
No. It uses the numbers you enter. Firms differ in how they measure the daily limit, whether the total limit trails the high point and how many days they give, so enter the rules from your own challenge.
What does attempts per pass mean?
It is 1 divided by the pass rate, for example about 1.8 attempts at a 55.6 percent pass rate. It counts fees paid per pass on average. It does not say any pass is likely.
Are the numbers on this page real?
Example numbers are made up to show how the maths works, and the page says so. A figure only counts as exact when the page says it was calculated on a stated date. Nothing you enter in a calculator leaves your browser.
Can I use this to decide whether to run a bot?
It can show whether a bot's numbers hold together and how much an account can lose. It cannot say what the market will do, and it is not advice. Use it to ask better questions, then read the terms of your own broker or exchange.
Is this financial advice?
No. It is a calculator and general education. It does not consider your situation, and its answers are only as good as the numbers you enter.
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