Buying Power (Excess Equity)

Buying power is the amount a broker currently shows as available for new trades, and excess equity is the account equity above the margin requirement. In a margin account, buying power is a broker calculation, not simply cash in the account.

Buying power matters because it can change quickly when prices move, margin requirements change, securities become less eligible, or a broker applies stricter house rules. It should be treated as a limit check, not as a reason to trade.

Key Takeaways

• Buying power depends on cash, securities value, margin debt, and current margin requirements.
• Excess equity is the cushion above the requirement; it can shrink as collateral value falls.
• Broker-displayed buying power may differ by asset class, order type, concentration, and account permission.
• Available capacity can fall even if the investor does not place a new trade.
• Buying power is not reliable liquidity and may not be withdrawable cash.

Buying Power vs. Excess Equity

Example

An account holds $40,000 of eligible stock and has a $10,000 margin loan. Account equity is $30,000 before interest or other adjustments. If the broker requires $12,000 of equity for the current positions, the account has $18,000 of excess equity.

That does not mean the investor can safely spend $18,000. The broker may translate excess equity into different buying-power amounts for listed stocks, options, concentrated positions, short sales, or non-marginable securities. If the stock value falls, both equity and displayed buying power can fall immediately.

What Changes Buying Power?

• market value of current positions
• new trades, open orders, or unsettled transactions
• margin interest and fees
• position concentration or volatility
• security eligibility and non-marginable holdings
• broker house requirements
• short-sale borrow constraints or option strategy requirements

How To Evaluate It

Before using displayed buying power, check:

• whether it is for marginable securities, options, day trades, withdrawals, or another use
• whether open orders already reserve part of the capacity
• whether concentrated or volatile positions face stricter requirements
• whether the broker’s margin screen uses real-time or delayed values
• whether the trade would leave a cushion after a plausible adverse price move

Official Sources

• FINRA: Margin Accounts
• SEC: Margin, Borrowing Money to Pay for Stocks
• FINRA Rule 4210: Margin Requirements

Related Terms

• Margin Account: Account type where buying power can include broker credit.
• Margin Loan Availability: Remaining borrowing capacity after current requirements.
• Margin Debt: Amount already borrowed from the broker.
• Maintenance Margin: Required equity to keep a margin position open.
• Non-Marginable Securities: Holdings that may reduce or eliminate borrowing capacity.