Margin equity is the dollar value you actually own in a margin brokerage account: the current market value of your securities minus the debit balance you owe your broker. It is the number that decides whether you can place new trades, whether you’re about to get a margin call, and whether the broker is about to sell your positions without asking.
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, based on the last traded price. The debit balance is what you owe the broker: the original loan plus accrued interest and fees. That debit balance grows daily as interest compounds, which new margin traders often miss.
Say you buy $40,000 of stock using $20,000 of your own cash and $20,000 borrowed from the broker. Market value is $40,000, debit balance is $20,000, equity is $20,000. If the stock climbs to $50,000, equity rises to $30,000. If it drops to $30,000, equity shrinks to $10,000. The loan doesn’t shrink with your losses.
Margin Equity Percentage
Brokers don’t just watch the dollar figure. They divide margin equity by market value to get a percentage, and that percentage is what gets compared against regulatory and house thresholds. In the example above, $20,000 in equity on a $40,000 position is 50%.
When the stock falls to $30,000, equity of $10,000 works out to about 33%. A further slide to $26,000 leaves $6,000 in equity, or roughly 23%, below the federal maintenance floor. The percentage drops faster than the market value because leverage cuts in both directions with equal force.
What You Need to Open the Position
Federal Reserve Board Regulation T sets the initial margin requirement at 50% for most equity securities.1eCFR. 12 CFR 220.12 – Supplement: Margin Requirements 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. Certain low-priced stocks, newly issued shares, and other thinly traded securities can’t be bought on margin at all and must be paid for in full even inside a margin account.3FINRA. Margin Regulation You can still hold them, but they generate no borrowing power.
Maintenance Margin and Margin Calls
Once the position is open, your equity percentage has to stay above a floor called the maintenance margin. FINRA Rule 4210 sets that floor at 25% of market value for long equity positions.4Financial Industry Regulatory Authority. FINRA Rule 4210 – Margin Requirements Most brokers set their own house requirements higher, often between 30% and 40%, to keep a buffer above the regulatory minimum.
When your equity drops below the broker’s maintenance requirement, you get a margin call demanding you restore equity. You can deposit cash, add eligible securities, or sell 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 give you far less time.4Financial Industry Regulatory Authority. FINRA Rule 4210 – Margin Requirements
Take that same $40,000 position with a $20,000 debit. If the house requirement is 30%, minimum equity has to equal 30% of market value. At a market value of $28,000, your equity is $8,000, or about 28.6%. That triggers a call, and the broker calculates the deposit needed to lift the percentage back to 30%.
Forced Liquidation
Here is where margin accounts get genuinely dangerous. Your broker can sell your securities without contacting you first. Brokers are not required to issue a margin call before liquidating, and they can sell enough to pay off the entire loan, not just enough to meet the minimum.5FINRA. Know What Triggers a Margin Call The broker picks which positions get sold, not you. In a fast-declining market, your best long-term holdings can end up dumped at the worst possible price.2U.S. Securities and Exchange Commission. Understanding Margin Accounts
How Margin Equity Controls Buying Power
Margin equity directly sets how much additional stock you can buy, a figure brokers call buying power. Under Reg T’s 50% initial requirement, every dollar of excess equity above the maintenance threshold gives you roughly two dollars of buying power.1eCFR. 12 CFR 220.12 – Supplement: Margin Requirements With $10,000 in excess equity, you can buy about $20,000 of new margin-eligible securities.
Buying power moves in real time with market prices. A bad day doesn’t just threaten a margin call; it also shrinks the amount you can put to work going forward. If equity falls below the maintenance requirement, buying power goes to zero until you restore the account.
Short Positions Use a Different Formula
If you sell short, the standard equity formula flips. The broker lends you shares to sell, and the sale proceeds plus your deposit go into a credit balance:
Short Margin Equity = Credit Balance − Current Market Value of Short Position
With shorts, rising prices are the danger rather than falling ones, because a rising price means it costs more to buy the shares back. FINRA’s maintenance requirements for short positions can differ from long positions, and brokers frequently impose higher house requirements on shorts because the theoretical loss on a short is unlimited.
The Pattern Day Trader Threshold
If your account is flagged as a pattern day trading account, the equity rules get significantly stricter. FINRA requires pattern day traders to maintain at least $25,000 in margin equity on any day they place day trades.6FINRA. Day Trading That $25,000 can be a mix of cash and eligible securities, but it must already be in the account before you trade, not deposited after.
If equity drops 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. Some brokers set their own minimums above $25,000.6FINRA. Day Trading
What Moves Your Equity Day to Day
Four forces push margin equity up or down on any given day. Price movement is the biggest: rising prices increase market value and equity, falling prices reduce both. Cash deposits raise equity by reducing the effective debit balance; withdrawals do the opposite. Dividends received on your holdings add to equity. And interest accrued on the debit balance chips away at equity every single day.
Interest accrues on the borrowed amount daily, calculated using a 360-day year by industry convention. Because the interest continuously grows the debit balance, it continuously shrinks your margin equity, even on days when the market doesn’t move. Over months or years, that drag is meaningful and makes margin less attractive for long-term buy-and-hold strategies.
A stock that drifts sideways for months still produces a slow decline in equity percentage because interest keeps growing the debit balance. The only way to arrest that slide without selling is to deposit cash or collect enough in dividends to offset the interest cost.
Tax Notes When Equity Gets Wiped Out
A forced liquidation during a margin call is still a taxable sale. When your broker sells stock to cover a deficiency, the tax treatment is the same as if you had sold voluntarily: capital gain if the shares went up from your basis, capital loss if they went down, subject to the usual wash-sale and loss-limitation rules. The involuntary nature of the sale doesn’t change any of that.
On the other side, margin interest you pay may be deductible as an investment interest expense. IRS rules let you 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.8Internal Revenue Service. Form 4952 – Investment Interest Expense Deduction You have to itemize to claim the deduction and file Form 4952 with your return.