Margin equity is the dollar amount you actually own in a margin brokerage account: the current market value of your securities minus the debit balance you owe your broker. That single figure determines whether your account is in good standing, how much more you can buy, and whether your broker is about to sell your holdings to cover the loan.
The Formula
Every margin account runs on one equation:
Margin Equity = Market Value of Securities − Debit Balance
Market value is what your holdings are worth right now at the last traded price. The debit balance is the total you owe your broker: the original loan plus any accrued interest and fees. That balance grows daily as interest compounds, something new margin users often miss.
Say you buy $40,000 of stock using $20,000 of your own money and $20,000 borrowed from the broker. Market value is $40,000, debit balance is $20,000, and margin equity is $20,000. If the stock climbs to $50,000, equity rises to $30,000 because the loan stays the same. If the stock drops to $30,000, equity shrinks to $10,000. The loan doesn’t shrink with your losses.
Why the Equity Percentage Matters More Than the Dollar Figure
Brokers translate your equity into a percentage by dividing margin equity by the market value of your securities. In the example above, $20,000 divided by $40,000 is 50%. That percentage is what brokers compare against regulatory and internal thresholds to decide whether your account is compliant.
When the stock drops to $30,000, the math changes fast: $10,000 in equity over $30,000 in market value is roughly 33%. A further decline to $26,000 in market value would leave $6,000 in equity, about 23%, which falls below the federal maintenance floor. Percentage declines accelerate as market value drops, because leverage works against you with the same force it worked for you on the way up.
How Much Equity You Need to Open a Position
Before you can borrow to buy, you have to put up a minimum share of the purchase price yourself. Federal Reserve Board Regulation T sets that initial margin requirement at 50% for most equity securities.1eCFR. 12 CFR 220.12 – Supplement: Margin Requirements So to buy $40,000 of stock on margin, you need at least $20,000 of your own money in the account.2U.S. Securities and Exchange Commission. Understanding Margin Accounts
Some brokers require more than 50% for volatile or concentrated positions. And not every security qualifies for margin borrowing. Certain low-priced stocks, newly issued shares, and other thinly traded securities have to be paid for with 100% of your own funds even inside a margin account.3FINRA. Margin Regulation You can hold them, but they generate no borrowing power.
Maintenance Margin, Margin Calls, and Forced Liquidation
After you open a leveraged position, your account has to stay above a minimum equity percentage called the maintenance margin. FINRA Rule 4210 sets that floor at 25% of current market value for long equity positions.4Financial Industry Regulatory Authority. FINRA Rule 4210 – Margin Requirements Most brokers set their own house requirements higher, often in the 30% to 40% range, to give themselves a buffer.
When your equity percentage drops below the broker’s requirement, the broker issues a margin call. You can restore equity by depositing cash, adding eligible securities, or selling holdings to pay down the debit balance. FINRA rules allow up to 15 business days to resolve a general margin deficiency, but individual brokers almost always impose much shorter deadlines.4Financial Industry Regulatory Authority. FINRA Rule 4210 – Margin Requirements
Take the $40,000 position with a $20,000 debit balance. If the broker’s house maintenance requirement is 30%, minimum equity is 30% of market value. At a market value of $28,000, your equity is $8,000, or about 28.6%, which triggers a call. The broker will calculate the deposit needed to bring the percentage back to at least 30%.
This is where margin accounts get dangerous. Your broker can sell your securities without asking first. Brokers are not required to issue a margin call before liquidating, and they can sell enough to pay off the entire loan rather than just enough to meet the minimum.5FINRA. Know What Triggers a Margin Call The broker picks which positions to sell. In a fast-declining market, your best long-term holdings can be dumped at the worst possible price.2U.S. Securities and Exchange Commission. Understanding Margin Accounts
Buying Power
Margin equity directly controls how much more stock you can buy, a figure brokers call buying power. Under Regulation T’s 50% initial requirement, every dollar of excess equity above the maintenance requirement gives you roughly two dollars of buying power.1eCFR. 12 CFR 220.12 – Supplement: Margin Requirements If your account has $10,000 in excess equity, you can buy up to about $20,000 in new margin-eligible securities.
Buying power moves in real time. A bad day for your portfolio doesn’t only threaten a margin call; it also shrinks what you can invest going forward. If equity falls below the maintenance requirement, buying power goes to zero until you restore the account.
What Moves Your Equity Day to Day
Four forces push margin equity up or down. Price movement is the biggest: rising prices lift market value and equity, falling prices cut both. Cash deposits raise equity by reducing the effective debit balance; withdrawals do the reverse. Dividends received on your holdings add to equity. And interest charged on the debit balance erodes equity every single day.
Margin interest accrues daily on the borrowed amount, and the standard industry convention calculates it using a 360-day year. On a $30,000 loan at 6% annual interest, the daily charge is about $5.00, or roughly $150 a month added to the debit balance regardless of whether your positions move. Rates typically vary with loan size and the prevailing benchmark, with larger balances qualifying for lower rates. Because interest keeps increasing the debit balance, it keeps reducing your equity, even on days the market doesn’t move. Over months and years, that drag is meaningful and makes margin a poor fit for long-term buy-and-hold strategies.
Short Selling Uses a Different Formula
Short positions flip the equation. When you sell short, the broker lends you shares, and the sale proceeds plus your initial deposit sit in a credit balance. The formula becomes:
Short Margin Equity = Credit Balance − Current Market Value of Short Position
With shorts, rising prices are the danger. FINRA’s maintenance requirements for short positions can differ from long positions, and brokers often impose higher house requirements on shorts because the theoretical loss is unlimited.
The $25,000 Rule for Pattern Day Traders
If your account is flagged as a pattern day trading account, the equity rules tighten significantly. FINRA requires pattern day traders to keep at least $25,000 in margin equity on any day they place day trades.6FINRA. Day Trading The $25,000 can be a mix of cash and eligible securities, but it has to be in the account before you start trading, not deposited afterward.
If equity dips below $25,000, the account is frozen for day trading until you restore it. Many brokers won’t let you trade on margin at all in that situation, limiting you to cash-only transactions. Some brokers set their minimums above $25,000.6FINRA. Day Trading If you fail to meet a pattern day trader margin call within five business days, the restriction extends to 90 days of cash-only trading.4Financial Industry Regulatory Authority. FINRA Rule 4210 – Margin Requirements
Tax Treatment of Margin Sales and Interest
A forced liquidation during a margin call is still a taxable sale. Your broker selling stock to cover a deficiency is treated the same as a voluntary sale. If the shares sold for more than you paid, you owe capital gains tax on the difference. If they sold at a loss, you can claim a capital loss, subject to the usual wash sale and loss limitation rules. The involuntary nature of the sale doesn’t change the tax treatment.
Margin interest you pay may be deductible as an investment interest expense. Under IRS rules, you can deduct investment interest up to the amount of your net investment income for the year.7Internal Revenue Service. Publication 550 – Investment Interest Expense Net investment income generally includes interest and ordinary dividends but excludes long-term capital gains and qualified dividends unless you elect to include them. Any margin interest you can’t deduct in the current year carries forward to future years.8Internal Revenue Service. Form 4952 – Investment Interest Expense Deduction You have to itemize deductions to claim the benefit, and you file Form 4952 with your return.