How margin trading works

A margin account lets an investor buy eligible securities with personal cash and money borrowed from the broker. The securities in the account serve as collateral for that loan.

At a 50 percent initial margin, the investor supplies half of a new purchase. With $10,000 of cash, buying power is $20,000 and the borrowed amount is $10,000. The account then contains an asset worth the purchase amount and a loan owed to the broker.

The loan does not rise and fall automatically with the security price. If the market value falls, the debt is still due, so the investor's account equity absorbs the change first. How stocks work covers the ownership instrument. This page covers the credit wrapped around a margin purchase.

If cash is $C$ and the required initial margin share is $m$, then

$$\text{Buying power} = \frac{C}{m}$$

and

$$\text{Borrowed} = \text{buying power} - C$$

For the standard United States Regulation T illustration, $m = 0.50$. That turns $10,000 into $20,000 of buying power and leaves $10,000 borrowed. A broker can require a larger cash share, and some securities are not eligible for margin at all.

The leverage ratio calculator makes the borrowed share visible. How leverage ratio works owns the broader ratio. Here, financial leverage comes from the broker loan inside the position.

Margin account equity is market value minus the outstanding broker loan:

$$\text{Account equity} = \text{market value} - \text{margin loan}$$

A price gain increases account equity while the loan is unchanged, before interest and other costs. A price loss reduces account equity by the same market movement while the same loan remains payable. That is the leverage effect: the investor's equity changes faster in percentage terms than the security itself.

Equity is the residual after the debt claim. It can become a smaller share of the account even though the number of shares has not changed.

Initial margin governs the opening purchase. Maintenance margin governs the minimum equity share that must remain afterward. They are different tests.

When market losses push account equity below the applicable maintenance requirement, the broker can issue a margin call. The account holder may have to add cash, add eligible securities or reduce the position. The agreement can also permit the broker to sell assets without waiting for the account holder to choose what is sold.

Broker house requirements can be higher than regulatory minimums and can change for a security or account. A position that meets one requirement can fail a stricter one.

The second worked example applies the same formula to a hypothetical 25 percent initial requirement. The same $10,000 then supports $40,000 of buying power and $30,000 is borrowed.

That example is a sensitivity test, not the standard Regulation T initial requirement and not a recommendation. It shows why a lower cash share creates more leverage: the asset position is larger relative to the investor's cash, and the fixed loan claim is larger.

A maintenance percentage should not be inserted into the opening formula as though it automatically authorizes a purchase. The account's initial and maintenance rules each apply at their own stage.

The broker charges interest on the margin loan. That cost reduces the investor's return and continues while the borrowing remains outstanding. A variable borrowing rate can change the cost even when the loan balance is unchanged.

Distributions from a security can help cash flow, but they do not remove the loan or guarantee that maintenance requirements will be met. A broker sale after a margin call can also lock in a loss at a time the investor did not choose.

The two worked accounts isolate initial buying power: $10,000 at 50 percent supports $20,000 with $10,000 borrowed, while the hypothetical 25 percent case supports $40,000 with $30,000 borrowed. Margin eligibility, rates, house rules and loss capacity belong in any real decision. This is educational material, not financial advice.