Available buying power
Your available buying power is the cash in the account, less the margin currently reserved against open and pending short positions:
(deposits − withdrawals + credits − debits − fees) − maintenance margin
- maintenance margin
- Capital reserved against open and pending short positions (below)
Before any order is accepted, the simulator projects your buying power including all existing pending orders plus the new one. If the result would go negative, the order is rejected on the spot. The same projection comes back as a buying-power preview on the order ticket, broken into the change in margin and the change in available buying power.
Maintenance margin by position type
Every short leg reserves margin according to its structure. Defined-risk spreads are cheap; a condor never doubles up; a covered or debit position reserves nothing at all.
- Naked short option
strike × 20% × qty × 100Not accepted — see below- Credit vertical spread
spread width × qty × 100- Iron condor
max(call-side, put-side)The larger side, not the sum- Debit vertical spread
0The long leg covers the short- Covered position
0The long leg covers the short
A put spread and a call spread around the price. Only the larger side is reserved — never the sum.
Reserved margin
Sum of both sides
Not reserved — SPX can't lose on both sides at once
Left of $100,000
Starting capital after the margin reserve — before the order's own premium and fees move cash
A 1-lot iron condor with a 20-point put spread and a 15-point call spread reserves $2,000 — the larger side — not the $3,500 sum of both sides.
A few things worth internalizing:
- Defined-risk spreads are cheap. A credit vertical reserves only the spread width; a debit vertical needs no maintenance margin at all, because the long leg fully covers the short.
- Iron condors don't double up. The underlying can't finish below the put spread and above the call spread at once, so only the larger side's margin is reserved — never the sum.
- Naked shorts are the exception you'll never hit. The formula above describes the FINRA requirement, but the platform is defined-risk only, so the order is rejected before margin ever matters.
naked short positions are not allowed, regardless of capital — add the matching long leg to make it a spread. The full rule lives on the orders page.Pending orders reserve margin too
When you place a pending limit or stop order that would open a short, its projected margin is reserved immediately — so your buying power reflects the commitment before the order fills. Cancel the order before it fills and the reserved margin is released.
Starting capital
Every account starts with the same fixed $100,000 — live accounts and bots at creation, every practice day, and every backtest session. There is nothing to choose: $100,000 comfortably supports the defined-risk spreads and condors traded here (a credit vertical reserves only its spread width in margin), and the shared figure keeps results comparable across strategies and account types. On a live account or bot the $100,000 is the genesis balance only — from there the cash balance carries and compounds day to day.