Margin trading sounds like free leverage: borrow against the stock you already own, buy more, and multiply the upside. The borrowing part is real — brokers have offered it for decades — but so is the part most pitches skip, which is what happens the day the trade moves against you and the broker can sell your position without calling first. Below is a plain breakdown of how margin actually works, a hypothetical worked example, and a genuinely current wrinkle: the rule that used to govern who could day-trade on margin just changed. None of this is investment advice or a recommendation to use margin, or to buy or sell any specific security.

What “buying on margin” actually means

A margin account lets an investor borrow cash from their broker, using the securities already in the account as collateral, to buy more stock than their cash alone would cover. The Federal Reserve’s Regulation T sets the starting point: for most stock purchases, an investor must put up at least 50% of the purchase price in their own cash or eligible securities, with the broker lending the other 50%. That 50% initial margin effectively doubles buying power — $10,000 in cash can control $20,000 of stock. FINRA Rule 4210(b)(4) separately requires a $2,000 minimum account equity before a broker can extend any margin credit at all, regardless of the Reg T math.

The loan isn’t free. Brokers charge interest on the borrowed amount — a margin interest rate, typically a few points above a benchmark rate, that accrues daily whether the trade is working or not. And the 50% figure isn’t a one-time hurdle; it’s followed by an ongoing requirement called maintenance margin, which is where margin trading actually gets risky.

A worked example, with hypothetical numbers

Say a hypothetical stock, “XYZ Corp,” trades at $100 a share. An investor has $10,000 in cash and wants more exposure, so instead of buying 100 shares outright, they use margin to buy 200 shares: $10,000 of their own cash plus a $10,000 margin loan from the broker, for a total position of $20,000.

  • XYZ rises to $115 (up 15%): the position is worth $23,000. After repaying the $10,000 loan, the investor’s equity is $13,000 — a $3,000 gain on $10,000 of their own cash, or 30%. Margin doubled the percentage return compared to buying 100 shares with cash alone, which would have returned 15%, or $1,500.
  • XYZ falls to $85 (down 15%): the position is worth $17,000. After the $10,000 loan, equity is $7,000 — a $3,000 loss, or 30% of the original $10,000, compared to a 15% loss ($1,500) had the investor used cash only. The loss is doubled in the same way the gain was.
  • XYZ falls to $65 (down 35%): the position is worth $13,000. Equity after the loan is just $3,000 against a $13,000 position — roughly 23%. That crosses below the maintenance floor most brokers enforce, which triggers a margin call.

The maintenance call — and why it can sell you out without asking

FINRA Rule 4210 sets a maintenance margin floor of 25% of the current market value of the securities in a long margin account — meaning the investor’s equity can never fall below a quarter of what the position is currently worth. Most brokerage firms set their own “house” maintenance requirement higher, commonly 30% to 40%, as a buffer above the regulatory minimum. When equity drops below that threshold, the broker issues a margin call, demanding the investor deposit more cash or securities to restore the account.

The part that catches people off guard: a brokerage agreement typically gives the firm the right to sell securities in the account to cover a margin call without contacting the investor first, and without regard to which specific positions get liquidated or any tax consequences that creates. The investor doesn’t get to choose what’s sold, and in a fast-moving decline, a broker can liquidate the same day the equity threshold is breached. That’s the mechanical reason margin calls are described as forced-liquidation risk rather than a simple request for more cash.

What actually changed in 2026

For two decades, FINRA Rule 4210 also carried a separate, specific provision for frequent traders: anyone who made four or more “day trades” (buying and selling the same security within one session) within five business days was classified a “pattern day trader” and required to maintain at least $25,000 in account equity, with trading privileges suspended until that minimum was restored if the account fell below it. That fixed-dollar rule is gone. The SEC approved FINRA’s amendments to Rule 4210 removing the pattern day trader designation and the $25,000 minimum entirely, replacing them with a new intraday margin framework tied to an account’s actual real-time market exposure rather than a flat dollar floor. FINRA published the implementation details in Regulatory Notice 26-10, with the new framework taking effect June 4, 2026.

What didn’t change: Rule 4210’s standard 25% maintenance margin floor for ordinary (non-day-trading) margin positions, Regulation T’s 50% initial margin on new purchases, and the separate $2,000 minimum equity needed to open margin privileges at all. In other words, the $25,000 threshold that kept smaller accounts out of frequent day trading is gone, but the underlying math that makes margin risky for anyone — the 50% initial deposit, the 25% maintenance floor, and the broker’s right to liquidate — is exactly the same as it was before.

The bottom line

Margin is a real tool that professional traders and disciplined investors use deliberately, with position sizes and stop-losses chosen in advance. The mechanics above are the actual, learnable rules: a 50% initial deposit, interest that accrues daily on the borrowed half, a 25% regulatory maintenance floor (often higher at individual brokers), and a broker’s contractual right to sell an account’s holdings without advance notice if that floor is breached. The 2026 removal of the $25,000 pattern-day-trader minimum changed who can trade frequently on margin — it did not change how much a leveraged position can lose, or how fast.

This article is for educational purposes only and does not constitute investment advice. Always do your own research or consult a licensed financial advisor before making investment decisions. See our Financial Disclaimer for more.

Photo by Arturo Añez / Unsplash.