Risk budget = account balance × risk %. Loss per unit = |entry − stop| + (fee + slippage) × (entry + stop), with rates in fractions. The raw quantity is the lesser of risk budget / loss per unit and account balance × maximum exposure / entry. Quantity is then rounded down to the entered increment (zero disables rounding). Fees are charged on both entry and exit notionals. Net P&L = quantity × [direction × (exit − entry) − (fee + slippage) × (entry + exit)], where direction is +1 for long and −1 for short. Slippage is an explicit proportional cost buffer on both notionals. The exposure cap limits gross notional; it is not a broker margin model. This sizes linear USD-quoted shares or coins, not inverse contracts or futures multipliers. A stop price is an input, not a guaranteed fill; gaps, borrowing, margin and funding are excluded.

CME Group: position sizing · Coinbase: maker fees and rebates