Why can you have enough money to buy stocks, yet later need to reduce the position? What do initial margin and maintenance margin each require?

Initial margin mainly determines whether you can open or increase a position; maintenance margin determines whether your account can continue to support existing positions. A fall in share prices reduces account equity. Higher broker margin requirements can also reduce your cushion.

We will use one hypothetical example throughout: you contribute $50,000, borrow another $50,000 from your broker, and buy $100,000 of stock. First, we will calculate what happens when the shares fall, then explain why adding $2,000 in cash and selling $2,000 of stock have different effects.

This article covers purchases of marginable US stocks in a standard Regulation T (Reg T) margin account. Reg T is one of the US rules governing securities credit; its initial margin requirement is explained below. These calculations do not apply directly to short selling, options, futures, or portfolio margin accounts.

1. Stock value, borrowing, and account equity

Buying stocks on margin means combining your own money with money borrowed from your broker. The market value of the shares in your account is not all your own capital.

Suppose you contribute $50,000, borrow $50,000, and buy $100,000 of stock:

• Stock market value: $100,000;
• Loan balance: $50,000;
• Account equity: $50,000.

In this simplified account containing only stocks and a loan:

Account equity = stock market value − loan balance.

Think of equity as what would remain if you sold all the shares at that price and repaid the loan, ignoring fees for now.

Share price movements change the stock value and your equity, but the loan principal does not rise or fall in proportion to the shares.

Initial and maintenance margin both specify how much equity an account needs, but serve different purposes:

Concept	Question it answers	How it applies here
Stock market value	What are your shares worth now?	Initially $100,000
Account equity	How much is yours after deducting the loan?	Initially $50,000
Initial margin	How much equity is needed to open or increase a position?	At an assumed 50% requirement, buying $100,000 of stock requires $50,000 in equity
Maintenance margin	How much equity must you retain to support existing positions?	An assumed 40% of the position’s current market value

Margin here is not a fixed deposit handed to the broker. It is the equity your account must maintain, which is different from the amount borrowed.

2. How do the 50% initial and 25% maintenance requirements differ?

For ordinary purchases of marginable stocks covered by Reg T, Federal Reserve rules generally require 50% initial margin.

Buying $100,000 of stock generally requires at least $50,000 of your own equity; the remaining amount may be financed.

Once you hold the shares, you must also meet maintenance requirements. The SEC’s guide to margin accounts explains that FINRA generally requires equity of at least 25% of the current market value of the relevant long stock positions. Brokers can require more.

A regulatory minimum of 25% therefore does not mean every stock in your account needs only 25% equity, or that you can pay just 25% when buying it.

The calculations below use the same assumptions throughout:

• The initial margin requirement is 50%;
• The maintenance margin requirement stays fixed at 40%;
• The account holds only this eligible stock position;
• Interest, fees, and other assets are excluded for now.

The 40% rate is a hypothetical assumption for illustration, not the current requirement for any particular stock or account.

We will distinguish three things: the required percentage, the dollar amount of equity required, and the shortfall when actual equity is insufficient.

3. Why can a 20% stock decline mean a 40% equity loss?

The shares fall, but the loan principal stays the same

Initially, the shares are worth $100,000, with $50,000 of equity and a $50,000 loan.

If the shares fall 20%, the position is worth $80,000, but the loan principal remains $50,000:

Account equity = $80,000 − $50,000 = $30,000.

Your equity falls from $50,000 to $30,000, a loss of $20,000. As a percentage of your original contribution, the loss is:

$20,000 ÷ $50,000 = 40%.

In this example, a 20% stock decline produces a 40% loss on your own capital, before interest and fees.

Recalculate maintenance requirements using current market value

Assume the maintenance requirement is 40%. With the shares now worth $80,000, the required equity is:

$80,000 × 40% = $32,000.

Actual equity is only $30,000, leaving a shortfall of:

$32,000 − $30,000 = $2,000.

You can also express equity as a percentage of stock value:

Actual equity percentage = $30,000 ÷ $80,000 = 37.5%.

Since 37.5% is below the assumed 40% requirement, the account no longer meets this maintenance requirement.

The cushion can run out before the shares fall 20%

If your own equity must cover 40% of the stock value, borrowing can account for no more than the remaining 60%.

With the loan fixed at $50,000, the stock value at which the account just meets the requirement is:

Stock value at the maintenance threshold = $50,000 ÷ 60% ≈ $83,333.33.

A fall from $100,000 to approximately $83,333 is a decline of about 16.67%.

In other words, with these assumptions unchanged, a decline of roughly 16.67% reaches the maintenance threshold—you do not have to wait for a 20% drop.

This is a simplified calculation, not a liquidation price promised by the broker. Interest, fees, changing margin requirements, and other positions can all affect the account.

4. Why can a $2,000 shortfall require selling $5,000 of stock?

Adding cash and selling shares to repay borrowing change different parts of the account.

Continue with the same situation: $80,000 in stock, a $50,000 loan, and $30,000 in equity, leaving a $2,000 shortfall against the 40% maintenance requirement.

For the calculations below, ignore price changes, fees, transfer delays, and settlement timing. Assume all new cash or sale proceeds go toward repaying the loan.

Adding cash increases account equity

After adding $2,000 and using it to repay borrowing:

• Stock value stays at $80,000;
• The loan falls to $48,000;
• Account equity rises to $32,000.

The equity percentage becomes:

$32,000 ÷ $80,000 = 40%.

The account just meets the requirement in this model.

Selling stock to repay borrowing reduces the position and its maintenance requirement

If you sell $5,000 of stock and use all the proceeds to repay borrowing:

• Stock value falls to $75,000;
• The loan falls to $45,000;
• Account equity stays at $30,000.

The equity percentage becomes:

$30,000 ÷ $75,000 = 40%.

Selling $5,000 of stock does not mean losing another $5,000. Under these assumptions, you simply convert some shares into cash and use that cash to repay debt. The earlier share price loss is already reflected in account equity.

Here are the three account states side by side:

Item	Before action	Add $2,000 and repay debt	Sell $5,000 of stock and repay debt
Stock market value	$80,000	$80,000	$75,000
Loan balance	$50,000	$48,000	$45,000
Account equity	$30,000	$32,000	$30,000
Equity required at 40%	$32,000	$32,000	$30,000
Actual equity percentage	37.5%	40%	40%

The distinction is straightforward: adding cash increases equity; selling shares to repay debt reduces the position, lowering the amount of equity required.

If you sell only $2,000 of stock to repay borrowing, stock value falls to $78,000 and the loan to $48,000. Equity remains $30,000:

$30,000 ÷ $78,000 ≈ 38.46%.

That is still below 40%.

Both remedies above only bring the account exactly to the requirement, with no cushion. They also do not mean you will necessarily have time to carry out these transactions after a real shortfall develops.

5. Interactive Brokers: what to watch and why you cannot wait for a notice

Capacity to add positions and capacity to retain them are different

At Interactive Brokers (IBKR), start by distinguishing two balances:

• Available Funds: relates to initial margin requirements and helps show whether there is room to add positions;
• Excess Liquidity: relates to maintenance margin requirements and indicates the remaining maintenance cushion for existing positions.

For the securities segment of an account, IBKR defines Excess Liquidity as:

Equity with Loan Value − maintenance margin requirement.

Equity with Loan Value is the equity the broker recognizes under the applicable rules for supporting margin borrowing. It is not necessarily the net value of all account assets. In a complex account, total Net Liquidation Value cannot simply be substituted. If you hold assets in different account segments, such as securities and futures, check the corresponding figures separately.

Return to the original simplified example: after the purchase, equity is $50,000. If the initial margin requirement is also $50,000, the capacity for further purchases under that requirement is fully used.

However, the maintenance requirement is:

$100,000 × 40% = $40,000.

This still leaves:

$50,000 − $40,000 = $10,000 of maintenance cushion.

An account can therefore have no room to add positions while still meeting maintenance requirements for its existing holdings.

The cushion can shrink even without another price decline

Suppose the shares fall to $90,000 in value. With the loan still at $50,000, account equity is $40,000.

At a 40% maintenance requirement, the required equity is $36,000, leaving a $4,000 cushion.

If the broker raises the requirement to 45%:

$90,000 × 45% = $40,500.

Even without a further price decline, actual equity of $40,000 is now $500 short.

When your cushion shrinks, check both the prices of your holdings and the applicable margin requirements.

IBKR’s real-time controls do not guarantee time to add funds

IBKR’s margin guide describes real-time margin monitoring and liquidation. It generally does not follow a traditional margin-call process that first sends a notice and then allows several days to deposit funds.

If equity is insufficient to meet the applicable maintenance requirement, positions may be liquidated. The earlier $2,000 shortfall illustrates how the account changes; it should not be treated as a funding plan you can comfortably carry out after receiving a notice.

Other holdings in the same margin account are not automatically isolated from margin risk just because you label them an “unleveraged core position.” The SEC also notes that brokers may sell securities in the account to meet requirements without obtaining your prior consent.

6. Interest, intraday trading, and overnight positions

Interest depends on the relevant balance, not just hours held

Margin requirements and the amount borrowed are different things. Interest calculations depend on the applicable balance, rate, and calculation rules.

IBKR’s interest calculation guide uses relevant settled cash balances and other inputs to calculate interest. Holding a position for “two hours in the overnight session” alone does not tell you how much interest will be charged, or establish that no interest will be due.

Consider a separate hypothetical example: a US dollar loan balance remains at $50,000 for 30 days, at an assumed fixed annual rate of 8%, using a 360-day basis:

$50,000 × 8% ÷ 360 × 30 ≈ $333.33.

The 360-day basis is an interest calculation convention, not a claim that a year has only 360 days. The actual basis depends on the currency and broker’s rules. The 8% rate is illustrative, not IBKR’s current quoted rate.

Intraday buying power and overnight capacity must be assessed separately

Standard Reg T stock purchases, intraday trading arrangements, and portfolio margin use different margin calculations. Intraday buying power is not automatically an overnight holding limit, nor does overnight trading necessarily allow a fixed 4× leverage ratio.

Intraday rules are also changing. FINRA Regulatory Notice 26-10 explains that the new intraday margin standards took effect on June 4, 2026, with a transition period through October 20, 2027, for firms needing more time. The arrangements that apply to a particular account also depend on the broker’s implementation.

For the margin positions discussed here, calculate three things first: the equity needed to open the position, the remaining maintenance cushion, and the daily cost of borrowing. These figures tell you more about the effect on your account than a general statement about “maximum leverage.”

Do not plan a position that only just meets the maintenance margin requirement. Adding $2,000 or selling $5,000 of stock in the earlier example only brings equity to exactly 40%, leaving no cushion. A further price decline, added interest or fees, or a higher broker requirement could create another shortfall.

Before deciding how much to borrow and buy, calculate how much room would remain after a further decline or an increase in margin requirements. If the only remedy would be a last-minute transfer, consider reducing borrowing or the position in advance. Money outside the account that has not yet arrived is not an available margin cushion.