Margin Call¶

OVERVIEW¶

A margin call is a broker's demand that a customer deposit additional cash or marginable securities into their account when the account's equity falls below the maintenance margin requirement. If the customer fails to meet the call within the broker's deadline (often same-day or T+1), the broker liquidates positions to restore compliance — frequently at the worst available prices and without any further notice. Margin calls apply only to margin accounts, not cash accounts, and are a structural risk of all leveraged trading.

HOW IT WORKS¶

Two regulatory layers govern margin in U.S. equities:

Layer	Requirement	Applied To
Reg T Initial Margin	50% of purchase price	New long positions
FINRA Maintenance Margin	25% of market value	Long positions
FINRA Maintenance Margin	30% of market value	Short positions
Broker House Margin	30–100% (varies)	Volatile or low-priced names

A margin call triggers when:

Account Equity / Market Value < Maintenance Margin %

The minimum stock price before a call is calculated as:

P_call = Loan Amount / (Shares × (1 − Maintenance %))

Worked Example — Long TSLA on Margin¶

Variable	Value
Shares purchased	100 @ $300 = $30,000
Cash deposited (Reg T 50%)	$15,000
Margin loan	$15,000
Broker house maintenance	30%
Margin call price	$214.29

P_call = $15,000 / (100 × (1 − 0.30))
P_call = $15,000 / 70
P_call = $214.29

If TSLA closes at $214.29 or below, the broker issues a call. At a $210 close: position value = $21,000 · equity = $6,000 · required equity = $6,300 · shortfall = $300. The customer must deposit $300 cash or approximately $1,000 of additional marginable securities to cure the call.

COMMON TRIGGERS¶

Scenario	Why a Call Occurs
Leveraged long positions	Sharp gap-down earnings or sector rotation
Short squeezes	Rising position value compounds losses faster than longs
Concentrated portfolios	Single-name drawdowns hit account equity disproportionately
Volatility expansion	Brokers hike maintenance requirements mid-trade without a price move
Options assignment	Short assignments deliver margined stock; underlying gaps create instant calls

Tip

During high-volatility events, brokers can raise house maintenance requirements to 100% with no notice — as seen with GME and AMC in January 2021. This creates margin calls on every leveraged holder regardless of current price action.

LIMITATIONS AND MISCONCEPTIONS¶

Misconception	Reality
Calls are not always negotiable	Brokers reserve the right to liquidate immediately under FINRA Rule 4210; the "call" is a courtesy, not a contractual delay
House margin can change without notice	Brokers raised maintenance on GME and AMC to 100% in January 2021, instantly creating calls on every leveraged holder
Cash account confusion	Margin calls apply only to margin accounts; cash accounts face Reg T good-faith violations and 90-day restrictions instead
Liquidation order is the broker's choice	The firm picks which positions to sell, often hitting the most liquid names first
PDT rule	Accounts under $25,000 flagged as PDT face additional margin restrictions independent of maintenance calls
Crypto and futures use different rules	Futures use SPAN margin with intraday calls; crypto exchanges auto-liquidate at 100% loss of posted collateral with no human in the loop