What this calculator does
It turns a risk amount and a stop distance into a number of contracts or lots, using the tick size and tick value of the instrument. It extends the general position size calculator with the two things a challenge adds: risk measured against the account size, and the share of today's daily loss budget that one stop-out would use.
Choose an instrument, or choose Custom and enter your own values. Then set the risk per trade, either as a percent of the account size or as a percent of the daily budget you have left today, and the distance to your stop. The calculator returns the size rounded down to the smallest step, the amount actually at risk, the share of the daily budget it uses and, if you add a target distance, the reward and the R-multiple.
The instrument values are examples
The presets are common textbook values: E-mini S&P 500, 0.25-point tick worth $12.50; its micro, $1.25; E-mini Nasdaq-100, $5.00; its micro, $0.50; gold futures, a 0.10 tick worth $10; crude oil, 0.01 worth $10; and a USD-quoted forex pair at $10 per pip per standard lot. Contract specifications, margins and the value of a pip for non-USD pairs vary by broker and change over time. Treat every preset as an example and verify it with your broker before using the result. All fields stay editable.
What it assumes
The stop fills at its price and a loss costs exactly the stop distance times the tick value plus any costs you enter. Real fills include slippage, and some firms count commissions and fees in the daily limit. Size is rounded down, so the real risk is at or below the amount you set. Firms differ and change their rules, so enter the daily limit from your firm's current terms. This page is not affiliated with any prop firm.
The math
The second basis, risk as a percent of what is left in the daily budget, makes size shrink on its own as the day goes badly. It is a way of tying the size of a trade to the room you have left, which is the quantity a daily loss limit actually constrains.
Worked examples
One ES contract or ten micros
$100,000 account, 0.5% risk ($500), 10-point stop, target 20 points. Only the contract changes.
| Contract | Tick value | Loss per contract | Size | Actual risk | Reward at target |
|---|---|---|---|---|---|
| E-mini S&P 500 (ES) | $12.50 | $500 | 1 | $500 | $1,000 |
| Micro E-mini S&P 500 (MES) | $1.25 | $50 | 10 | $500 | $1,000 |
Both land on the same dollar risk and the same 1 : 2 reward-to-risk. The micro contract gives finer control: at a risk where ES rounds down to a whole contract, micros let you size to the dollar.
A forex trade in lots
$100,000 account, 1% risk ($1,000), a 20-pip stop on a USD-quoted pair (0.0020 in price) with a pip worth $10 per standard lot.
The loss per lot is 20 pips × $10 = $200, so the size is $1,000 ÷ $200 = 5 lots, or 500 mini lots. The same trade on a pair whose pip value is not $10 needs that pair's value in your account currency, which is why the tick value field is editable.
Sizing from what is left of the day
You have already lost $3,000 today on a 5% daily limit, so $2,000 of budget is left. You risk 20% of that on a micro trade with a 10-point stop.
The risk is $400 and the loss per MES contract is $50, so the size is 8 contracts and the actual risk is $400, which is 20% of the remaining budget. Early in the day, the same 20% would have been $1,000: size falls as the budget does.
Frequently asked questions
How do I calculate the position size for a prop firm challenge?
Decide how much you will lose if the stop is hit, in dollars. Divide it by the loss per contract or lot at your stop, which is the stop distance in ticks times the tick value plus costs, and round down. Then check that the loss is a small share of the daily loss budget you have left, because that is the limit a challenge adds to ordinary position sizing.
What risk per trade should I use on a challenge?
There is no single answer, because it depends on your edge, the daily limit and the drawdown rule. A useful sanity check is how many full losses in a row you can take inside the daily limit, which the daily loss limit calculator on this site shows. The challenge simulator shows how pass probability changes with risk size.
Should risk be a percent of the account or of the daily budget?
Both are used. A percent of the account size keeps risk steady. A percent of the remaining daily budget shrinks the size automatically as the day goes badly, so a run of losses cannot use up the limit as quickly. Use the selector to compare the two.
Are the tick values correct for my broker?
They are common example values and may differ for your broker, your account currency or a contract that was rolled or changed. Verify tick size and tick value with your broker, then type them into the editable fields.
Why is the size 0?
Because even the smallest size step would risk more than the amount you set. Use a tighter stop, a smaller instrument such as a micro contract or a smaller lot step, or a larger risk, or skip the trade. The calculator does not round up.
Does this calculator use my firm's rules?
No. It has no built-in rules from any firm. You enter the daily limit and how much of it has been used. Always read the current rules of the firm you trade with. This page is educational and is not affiliated with any prop firm.
Size is only half of a trade plan.
A stop placed by structure or volatility, and a target with room to run, decide how much size you can use. Indicators can help mark both.
Guides that explain it
Last updated November 2026. For education only. Not financial advice. Results depend on your inputs and cannot predict future performance.