Turn the risk percentage into a quote-currency budget
Multiply account equity by the chosen risk percentage, expressed as a decimal, to obtain the planned loss budget. This budget is the amount allocated to the modeled trade outcome at the stop. It is different from the amount of capital used to purchase or margin the position.
Use an account value that reflects the capital you actually intend to include in the calculation. A risk percentage does not have meaning without its denominator. If several positions share exposure to Bitcoin or the same market move, calculating each position independently does not measure the combined account risk.
Include costs in the loss per BTC
For a long position, the basic price loss per BTC is entry price minus stop price. Add the estimated entry and exit trading costs per BTC before dividing the loss budget by that total. The resulting quantity multiplied by the entry price gives the opening quote notional.
An entry price at or below the stop is not a valid input for this long-stop model. As the stop approaches the entry, the price-distance component becomes small, so fees and execution uncertainty become more significant. Ignoring them can materially overstate the quantity that fits the intended loss budget.
Compare planned risk with executable size
The calculated quantity is a theoretical size under the entered exit and cost assumptions. An exchange may require a quantity step, minimum notional or available balance that changes the executable order. Rounding upward increases exposure; rounding downward generally reduces the modeled risk.
A stop trigger is not the same as a guaranteed fill price. Check whether the intended order type can fill through the available depth and whether the position uses leverage. This tool does not calculate liquidation, available margin or portfolio drawdown, and it does not select the entry or stop for you.
Questions about this tool
Does using leverage reduce the amount I lose at the stop?
For the same BTC quantity and the same entry and exit prices, the price loss is unchanged. Leverage changes the collateral required and the margin constraints, which this position-size calculation does not model.
Why does a tighter stop produce a much larger position?
A smaller modeled loss per BTC allows more BTC within the same loss budget. That larger notional can become sensitive to fees, slippage and available margin, so the mathematical size still needs an execution check.