Brokerage Margin Account: How It Works, Requirements, and Margin Calls

A brokerage margin account is a type of investment account that lets you borrow money from your broker to buy securities, using the cash and investments already in the account as collateral. Federal rules let you borrow up to 50% of a stock’s purchase price, which roughly doubles your buying power compared with a cash account. The leverage runs both ways: profits are larger, losses are larger, and in a bad market you can end up owing your broker more than you originally put in.

How Margin Borrowing Works

When you buy stock on margin, you cover part of the purchase with your own money and borrow the rest. The securities and cash in your account secure the loan. Your equity is the market value of your holdings minus what you owe the broker. Hold $40,000 in stock bought with $20,000 of borrowed money, and your equity is $20,000.

Interest is charged on the borrowed amount, calculated daily and usually posted monthly. Rates vary across firms and generally float with a benchmark like the broker call loan rate, with lower rates on larger debit balances.¹ Interest keeps accruing for as long as the position is held on margin, so even a flat stock quietly costs you money.

What It Takes to Open One

Every brokerage account starts as a cash account. To add margin, you submit an application that gathers more detail than a standard opening. Federal anti-money-laundering rules require your taxpayer identification number and a government-issued photo ID.² FINRA’s know-your-customer rules then ask for annual income, liquid net worth, investment experience, and your stated objectives, which the firm uses to decide whether margin is appropriate for you.

You also need at least $2,000 in equity. That floor comes from FINRA Rule 4210, and no broker can go below it, though some set higher house minimums.³ Once that threshold is cleared, Federal Reserve Regulation T caps borrowing at 50% of the purchase price on new equity purchases. Buy $10,000 of stock and you put up at least $5,000; the broker lends the other $5,000.⁴

The central document is the margin agreement. It spells out the interest terms, your obligation to repay, and the pledge of your securities as collateral.⁴ Signing it also lets the broker hold your securities in street name, meaning registered in the firm’s name rather than yours, so they can be pledged or sold quickly. The liquidation clause matters most. Most agreements let the broker sell your holdings without consulting you first if the account falls below required levels.

Buying Power and Placing a Trade

Once approved, you select “Margin” instead of “Cash” when entering a buy order. The platform draws on your available buying power, which combines your cash equity with your borrowing capacity under Regulation T. With $10,000 of cash equity and no existing margin debt, your buying power for most stocks is about $20,000.

After the trade settles, the borrowed amount shows up as a debit balance and starts accruing interest right away. Each new margin purchase shrinks your remaining buying power and raises your exposure if prices drop.

Securities You Cannot Buy on Margin

Not every security is eligible. Common exclusions include:

Penny stocks, meaning shares trading below $5, because of volatility and thin volume.
Recent IPOs, typically for the first 30 days of trading.
Many over-the-counter bulletin board stocks that lack the liquidity brokers need to unwind quickly.
Securities held in retirement accounts such as IRAs and 401(k)s, which prohibit this kind of borrowing by design.

Individual brokerages can tighten these rules further. A stock that is marginable at one firm may be cash-only at another, particularly for volatile or thinly traded names. Non-marginable securities also do not count toward your equity for buying power purposes.

Maintenance Requirements and Margin Calls

After the purchase, you must keep a minimum level of equity in the account at all times. FINRA sets the floor at 25% of current market value, and many firms impose house requirements of 30% to 40%, with higher levels for volatile or concentrated positions.³

If your holdings fall in value, your equity shrinks while the loan balance stays put. Drop below the maintenance threshold and the broker issues a margin call. You can meet it by depositing cash, transferring in more securities, or selling positions to pay down the loan.

FINRA rules allow up to 15 business days to resolve a margin deficiency, but do not rely on that window.³ Most margin agreements let the broker liquidate your positions immediately, with no advance call and no deadline to wait on.⁴ The broker chooses which securities to sell and when. Forced sales typically happen during the same market drops that triggered the call, which works against you. You have no right to pick which positions get closed or to request more time.

What You Stand to Lose

The SEC specifically warns that margin investors can lose more than they originally deposited.⁴ Say you buy $50,000 of stock using $25,000 of your own money and the position falls to $15,000. Selling everything repays only $15,000 of the $25,000 loan. Your original $25,000 is gone, and you still owe the broker $10,000 plus accrued interest.

Leverage magnifies losses at the same rate it magnifies gains. A 20% decline in a fully margined account wipes out 40% of your equity. A 50% decline erases your equity and puts you into debt. If a forced liquidation does not fully cover the margin loan, you remain personally liable for the shortfall, and the broker can pursue that deficiency like any other debt.⁵ Daily interest keeps compounding through all of it, and because the broker can sell without warning, you may lose positions you had hoped to hold through a recovery.

Pattern Day Trader Rules

Active trading in a margin account triggers its own rules. If you make four or more day trades within five business days, and those trades make up more than 6% of your activity in the margin account during that period, the broker must flag you as a pattern day trader.⁶ A day trade is buying and selling the same security on the same day.

Pattern day traders must keep at least $25,000 of equity in the margin account at all times, and that balance has to be in place before any day trading starts.⁶ Drop below $25,000 and day trading is off limits until you top the account back up. Exceeding your day-trading buying power triggers a separate margin call with up to five business days to deposit funds; miss it and the account is restricted to cash trades for 90 days. A trader with $10,000 who runs a few quick round trips in a week can hit this without seeing it coming.

Short Selling Needs a Margin Account

Short selling is only available in a margin account, because the strategy involves borrowing shares from the broker to sell with the goal of buying them back lower.⁷ Regulation T requires a deposit equal to 150% of the position’s value when you open it, and maintenance requirements apply from there. Losses on a short are theoretically unlimited, because the stock you shorted can keep rising with no ceiling.

Deducting Margin Interest

Margin interest can be deductible on your federal return. Under 26 U.S.C. § 163(d), interest paid on money borrowed to buy taxable investments qualifies as investment interest expense, deductible if you itemize.⁸

The deduction is capped at your net investment income for the year. That generally includes ordinary dividends and taxable interest, but not long-term capital gains or qualified dividends unless you elect to treat them as ordinary income. Any amount you cannot use in the current year carries forward automatically. Interest on margin used to buy tax-exempt securities such as municipal bonds is not deductible at all. You report the deduction on IRS Form 4952, and your broker should list total margin interest charged on your year-end statement.

1
Interactive Brokers. US Margin Loan Rates Comparison
2
eCFR. 31 CFR 1023.220 – Customer Identification Programs for Broker-Dealers
3
FINRA. FINRA Rule 4210 – Margin Requirements
4
U.S. Securities and Exchange Commission. Investor Bulletin: Understanding Margin Accounts
5
Charles Schwab. What to Know About Margin
6
FINRA. Day Trading
7
Interactive Brokers. Short Selling and Margin
8
Office of the Law Revision Counsel. 26 USC 163 – Interest