What Is a Margin Account?

Michael Whitman · Trading since 2017, full-time since 2020 · Published 2026-09-06 · Updated 2026-10-04 · Reviewed 2026-10-04

How it works

A margin account is a loan facility attached to a brokerage account. You put up cash, the broker lends against it, and you hold a larger position than your own money would buy.

If you are new to investing, leave margin switched off. A cash account can lose what you put in; a margin account can lose more than that, and nothing on this page is needed to buy and hold a fund.

What makes it different from an ordinary loan is the collateral. The security for the loan is the position itself. If the position falls, the collateral falls with it — the thing backing the debt and the thing losing value are the same thing.

Nothing about the price changes because you borrowed to buy it. A price chart looks exactly the same whether you paid cash or borrowed most of the money. Leverage is applied to the outcome, not to the probability.

Two numbers govern the account. The initial requirement is what fraction of the purchase your own money must cover. Under Regulation T (12 CFR 220.12) that is 50% for a margin stock, so $10,000 of cash buys $20,000 of stock. FINRA Rule 4210 adds a floor: the account needs equity of at least $2,000 before the broker extends credit, except that you never have to deposit more than the cost of what you bought.

The maintenance requirement is the second number — the fraction your equity must stay above once the position is on. Under FINRA Rule 4210 the floor is 25% of the market value of the stocks you hold long. The same rule tells every firm to set its own house requirements, which can be higher on any stock, and Rule 2264’s disclosure says the firm can raise them “at any time” without advance written notice.

The margin maintenance arithmetic

Equity is what you would have left if everything sold right now: position value minus what you borrowed. The call comes when equity divided by position value falls under the maintenance fraction.

The call price has a short formula. Call price = loan ÷ (shares × (1 − maintenance fraction)). Bought with half your own money at a 25% requirement, that is a fall to two-thirds of the entry price, a 33.33% fall, which on a purchase at $75 puts the call level at exactly $50.

Borrowing three dollars for every one of your own removes the cushion entirely. Hold four dollars of stock per dollar of equity and the call price as a fraction of entry is 3 ÷ (4 × 0.75) = 1.0 — the maintenance line sits exactly at your entry price. That was the most a pattern day trader could extend intraday under FINRA’s old day-trading rules, which Regulatory Notice 26-10 replaced with intraday margin standards effective 4 June 2026, sized to actual exposure during the day. Because firms have until 20 October 2027 to phase the change in, a broker may still be running the old rules.

A worked example

Take $15,000 and buy $30,000 of stock: 400 shares at $75. You owe $15,000. The price falls 20% to $60, so the position is worth $24,000 and you still owe $15,000. Equity is $9,000, which is 37.5% of value — above 25%, no call, and you have lost 40% of your money on a 20% move.

Push the price down to $50, a fall of one third, and the position is worth $20,000 against the same $15,000 debt. Equity is $5,000, which is 25% of value. That is the call at FINRA’s minimum.

Now apply a house requirement instead. Same 400 shares and the same $15,000 loan:

A 40% house requirement halves the room. The call arrives after a fall of one sixth instead of one third, on the same position and the same loan.

What arrives is a demand, and any deadline on it is a courtesy, not a right. The margin disclosure every US broker must hand you under FINRA Rule 2264 says the firm “can sell your securities or other assets without contacting you”, that you do not get to choose what is sold, and that you are “not entitled to an extension of time on a margin call.” The same rule text adds that an extension may be available under certain conditions, but a customer has no right to one, and in a fast fall the firm can sell at once, picking what goes and when.

Meeting a margin call: cash against sales

Let the price in the example keep falling to $45. The position is worth $18,000, the loan is still $15,000, and equity is $3,000. A 25% requirement on $18,000 is $4,500, so the account is $1,500 short.

Depositing cash fixes it with $1,500. Cash adds to equity directly: $3,000 + $1,500 = $4,500, exactly 25% of $18,000.

Selling stock takes $6,000 of sales to fix the same shortfall. A sale repays loan and shrinks the position by the same amount, so equity stays at $3,000. The requirement only falls by 25 cents for every dollar sold: $3,000 = 25% × ($18,000 − $6,000). At a 25% requirement, meeting a call by selling takes four times the cash amount, and at a 40% requirement it takes two and a half times.

Two kinds of call behave differently. A maintenance call comes from FINRA’s floor or the firm’s house requirement, and FINRA Rule 4210 gives the firm at most 15 business days to collect it unless FINRA grants more time. A Regulation T call comes from the initial requirement on a new purchase: 12 CFR 220.4 says it must be met within one payment period, which only the firm’s examining authority can extend, on the firm’s application, and if it is not met the firm must sell enough to cover it (a shortfall of $1,000 or less excepted).

The loan also carries interest. On a position held for months that is a real drag, and it is charged whether the position is working or not.

The short side of a margin account

Every short sale lives in a margin account, and the requirements run the other way. Regulation T sets the initial requirement for a short sale at 150% of the stock’s value: the sale proceeds count as 100%, and you deposit the other 50%.

Sell 100 shares short at $50. The $5,000 of proceeds plus a $2,500 deposit leaves a $7,500 credit, and your equity is $7,500 minus the cost of buying the shares back. FINRA Rule 4210’s maintenance requirement for a short stock at $5 or more is the greater of $5 a share or 30% of its value.

Solve for the call. Equity falls to 30% of the position when $7,500 − 100 × price = 0.30 × 100 × price, which gives a price of $7,500 ÷ 130 = $57.69, a rise of 15.38%. At that price 30% is $17.31 a share, above the $5 floor, so the 30% test is the one that binds. A long position bought at the same leverage had a 33.33% cushion; the short has less than half that, and a rise has no ceiling. Short selling covers the rest of the mechanics.

The original data

How much is borrowed across the industry. Under FINRA Rule 4521, every member firm that carries customer margin accounts reports, as of the last business day of each month, the total of all debit balances in customers’ securities margin accounts. FINRA publishes the totals; the table and its download were read on 4 October 2026 from FINRA’s margin statistics page.

At the end of August 2026 the total was $1,453,832 million, about $1.45 trillion, against $1,059,723 million a year earlier: up 37.19%. Over the same month-ends the S&P 500 rose 18.98%, from 6,460.26 to 7,686.14 (Yahoo Finance daily closes, price only). The highest month-end in FINRA’s table, which runs from January 1997, was June 2026 at $1,502,072 million; July 2026 then fell 5.65% while the index slipped 0.13%. Customers also held $425,140 million of free credit balances in cash and margin accounts in August 2026.

The series is read here from February 2010, when FINRA began collecting it under Rule 4521 from all member firms; before that, FINRA and the New York Stock Exchange collected similar figures separately. FINRA also notes that some month-to-month variation may come from firms changing how they compute the balances. From February 2010 to August 2026 the total grew 5.51 times, from $263,657 million, while the S&P 500’s month-end close grew 6.96 times.

Margin debt moved with the market, and further. Across the 198 month-to-month changes from March 2010 to August 2026, the change in debit balances and the change in the S&P 500 went the same direction 148 times, 74.75%, and the two series of monthly changes had a correlation of 0.71. From the October 2021 high of $935,862 million to December 2022, debit balances fell 35.18% to $606,659 million while the index fell 16.63%. These are totals across all customers; they show how borrowing tracked prices, not what any one account did, and they say nothing about what the index does next.

The monthly table with the matching S&P 500 closes is published as the margin debit table.

Few video titles name it. In the 24,971-video search study behind this site, 3 titles name margin accounts, margin trading or buying on margin, at a median of 125,237 views.

When it fails

A stop-loss does not cap a margin loss. A stop is an instruction to trade at the market once a price prints. If the market opens through it, you are filled where it opened — and the shortfall is money you borrowed, so a large enough gap can leave the account owing more than it holds.

And most of the time nothing dramatic happens. Leverage simply makes an ordinary sideways stretch more expensive, because every cost — the spread, the interest, the round trip — is multiplied while the range is not.

The other failure is arithmetical rather than dramatic. A cash account cannot go below zero: the worst case is that the position becomes worthless. A margin account can, because the debt is fixed while the collateral is not. Owing the broker after a position closes is a real outcome, not a theoretical one, and it is the reason the deposit is not the maximum loss.

The failure that catches people is timing, not direction. The maintenance calculation runs on the broker’s clock. Being right about the company three weeks after being sold out of it is the same outcome as being wrong.

And a call met by selling shrinks the position faster than it feels. Four dollars of stock sold for every dollar of shortfall at the FINRA minimum means a modest call can take a large slice of the holding, at the worst prices of the move.

Related

Margin is the account; leverage is what you do with it, and the sizing math is identical. Short selling is a margin position whether you asked for one or not. The pattern day trader rule governed intraday buying power until June 2026, and settlement explains why a cash account behaves so differently.

This page is educational, not financial advice. Test every idea on your own charts before risking money.