Micro futures position sizing for prop accounts

Start with the remaining loss room

A $50K prop-account label does not mean $50,000 is available to lose. For example, a hypothetical account at $50,300 with an active loss floor of $49,800 has $500 of distance to that floor. If only $150 remains before a daily lockout, that nearer boundary matters first.

Distance to a boundary is not a trade budget: reaching the boundary may trigger a breach or lockout. Allow for existing positions, costs and a margin below the trigger. Recheck the current floor; an intraday trailing floor can rise with unrealized profit. At Boxcar, an end-of-day floor is still enforced against open-position losses during the session.

Sources: Boxcar: drawdown and daily loss limits · Boxcar: evaluation, simulated-funded and live stages

Convert MES and MNQ moves into dollars

A tick is the minimum price increment. MES and MNQ outright futures both move in 0.25-point ticks, so one index point equals four ticks. Their dollar values differ: a 10-point adverse move costs $50 per MES contract or $20 per MNQ contract before costs. Equal point distances are not equal dollar exposure or a measure of equal market volatility.

Sources: CME: Micro E-mini contract specifications

Include costs before rounding down

Planned loss per contract = (stop distance in points ÷ tick size in points) × tick value + round-trip commission + slippage allowance + any other per-contract charges.

Divide the chosen dollar budget by that per-contract amount and round down to a whole number. Measure the stop distance from the entry fill; if calculating before entry, account for possible entry slippage too. The stop should follow the trade's invalidation point. Changing the stop merely to make another contract fit changes the trade itself.

Sources: CME: calculating position size · Boxcar: supported futures and commissions

MES example: a $100 planning budget

This hypothetical example uses a $100 trade-loss budget, not a recommended amount or percentage. It assumes no other open positions, enough remaining account loss room, and sufficient enabled contract capacity.

Boxcar currently lists MES commission at $0.50 per side, or $1 per round trip, for simulated accounts. Assume an additional two ticks of adverse exit slippage: 2 × $1.25 = $2.50 per contract. The distances below are from the actual entry fill, so entry slippage is already reflected.

The table shows how a wider stop reduces the quantity that fits. Three contracts at the 8-point distance would total $130.50 and exceed the $100 budget. A zero result means the proposed trade does not fit these assumptions; rounding up to one does not fix that.

The slippage allowance is an assumption, not a maximum loss or a promised fill. CME stop-limit orders can remain unfilled; stops with protection can execute away from the trigger within their protection range. These are exchange order mechanics. Boxcar evaluation and simulated-funded orders do not enter live markets, so check the platform's simulated execution behavior separately.

Sources: CME: Micro E-mini contract specifications · Boxcar: supported futures and commissions · CME: stop-limit and stop-with-protection orders · Boxcar: evaluation, simulated-funded and live stages

Apply the account's enabled contract limit

A firm's maximum contract count is a permission limit, not a suggested position size. Reduce the calculated quantity if it exceeds the capacity left after other positions. Adding several trades also requires checking their combined possible loss against the same account boundaries.

At Boxcar, ten micros count as one mini for position-limit purposes. Scale simulated-funded accounts may have a lower enabled tier than the account size's full cap. Live accounts have separately confirmed permissions and costs; do not carry simulated-account settings into a live calculation.

Sources: Boxcar: account and position limits · Boxcar: supported futures and commissions