Margin calls: when they trigger, how to calculate them, what to do

A margin call is your broker telling you that the collateral behind your loan is no longer enough. Either you add money or securities, or the broker will reduce the loan by selling what you hold. Most investors meet their first margin call on a bad day in the market, which is exactly when a forced sale does the most damage.

The good news is that a margin call is not a surprise in the mathematical sense. Given your loan, your share count and the firm's maintenance requirement, you can calculate in advance the exact price at which a call will trigger, and how much it would take to cure it. Investors who know those two numbers before they borrow are rarely caught flat-footed.

This page derives the call-price formula, works through two examples, explains the difference between a Regulation T call and a maintenance call, and sets out what US rules (as of 2026) let your broker do when a call is not met. It is educational, not advice on whether to borrow.

Two kinds of margin call

People say "margin call" for several different demands. They come from different rules and have different deadlines.

Regulation T call (also called a federal or "fed" call). When you buy on margin, Regulation T requires you to deposit 50% of the purchase price. If the account doesn't already hold enough equity, the shortfall is a Reg T call. Under 12 CFR 220.4 it must be met within one payment period, which Regulation T defines as the standard settlement cycle plus two business days, so three business days after the trade date under T+1. If it isn't met, the broker must sell securities to cover it, unless the shortfall is $1,000 or less, in which case Regulation T does not require action. A firm can apply to its regulator for an extension in exceptional circumstances; that is the firm's request, not your right. A Reg T call has nothing to do with the price falling: it is about paying for what you bought.

Maintenance call (also called a house call or FINRA call). After a purchase, your equity has to stay above the maintenance requirement: at least 25% of the market value of long margin securities under FINRA Rule 4210, or the firm's higher house level. When a falling price, a withdrawal or a rise in the house requirement pushes equity below that line, you get a maintenance call. FINRA's rule says required margin must be obtained "as promptly as possible" and in any event within 15 business days, but that is an outer limit for the firm, not a grace period for you. Firms commonly give a few days, and in a fast market may give none.

Intraday margin deficit (from June 4, 2026). FINRA's replacement for the pattern-day-trader rule adds a third kind: a deficit measured after each trade during the day. It must be met as promptly as possible, and repeat late payers face a 90-day restriction. Firms may phase it in until October 20, 2027; details are in Pattern day trader rule: the legacy PDT test and the 2026 replacement.

Deriving the call price

A maintenance call triggers when equity drops below the maintenance fraction of market value. Write n for shares, P for price, L for the loan and m for the maintenance requirement:

Equity percentage is not the same as your loss from the purchase price, which is why the call often comes sooner than people expect. With 2:1 leverage at the start (50% equity), the price only needs to fall a third for equity to reach 25%.

That "sell four dollars to fix one" ratio surprises many investors. At a 25% requirement each dollar of deficiency takes four dollars of stock sales to clear; at 30%, about 3.33; at 40%, 2.5. It is also why a forced liquidation tends to sell much more than the deficiency itself.

What happens when a call is not met

FINRA's investor guidance is blunt, and every margin agreement says the same thing in legal language. Your firm:

• can sell your securities without notice to meet a call. It is not required to contact you first, even if it often does;
• decides which securities to sell. You don't get to choose;
• may raise its house requirement at any time, without advance notice, and that can create a call on its own;
• does not owe you an extension of time to meet a call.

These points must be spelled out in the margin disclosure statement that FINRA Rule 2264 requires firms to give customers. In practice, firms often liquidate more than the bare deficiency, sometimes the whole position, to get the account comfortably above the requirement. If the sale proceeds are less than the loan, which happens after a large gap down, you still owe the remaining debit.

Real-world patterns

Margin calls cluster. When a broad market falls quickly, many leveraged accounts cross their call prices at once, and forced selling adds pressure to the prices that caused it. Single stocks can do the same thing in miniature: after a bad earnings report, a stock that gaps down 25% overnight can send leveraged holders straight past their call price before the market opens, with no chance to act at the call price itself. Firms also tend to raise house requirements on a stock right after it becomes volatile, so calls can arrive even as the price stabilizes.

How to reduce the chance of a call

None of these is a recommendation; they are the levers the arithmetic gives you.

• Borrow less than the maximum. At 25% maintenance, starting at 70% equity instead of 50% moves the call price for a $50 stock from $33.33 to $20.00. (Check: a $3,000 loan on 200 shares gives $3,000 ÷ 150 = $20.)
• Know your firm's requirement for each holding, not just FINRA's 25% minimum.
• Keep cash or unmargined securities available, so a call can be met by deposit rather than by a forced sale at a low price.
• Diversify the collateral. A single stock can move far more than a broad portfolio.
• Watch the call price, not the purchase price. Calculate it when you open the position and recalculate when you add, sell or withdraw.

Margin call types compared

How Finabase helps

Finabase does not hold your account, calculate your broker's equity or receive margin calls, so your firm's platform is the authority on whether you have one. What Finabase can do is make the call price visible before it is reached. Work out your call price with the formula above, then set an alert on the stock just above it; alerts fire on live trades and arrive as a push notification in the Stock Master app or by email. A symbol page shows the live quote and chart, and the performers page shows which stocks are making the day's largest moves, the kind that create calls.

Frequently asked questions

How long do I have to meet a margin call?

It depends on the type and the firm. A Reg T call must be met within one payment period, about three business days after the trade under T+1. A maintenance call is due when the firm says, often within a few days, and the firm may sell immediately without waiting.

Can my broker sell my stock without telling me?

Yes. FINRA states that a firm can sell your securities without notice to meet a margin call, and that it chooses which ones to sell. Many firms try to contact you first, but they are not required to.

How do I calculate the price that triggers a margin call?

Divide your loan by the number of shares times one minus the maintenance requirement: P = loan ÷ (shares × (1 − m)). With a $5,000 loan, 200 shares and 25% maintenance, that is $5,000 ÷ 150 = $33.33.

Does depositing cash or selling stock fix a call faster?

A cash deposit cures the deficiency dollar for dollar; selling stock needs about deficiency ÷ maintenance % of sales, four times the shortfall at 25%. Either works if done in time, but selling realizes gains or losses and shrinks the position.

Can a margin call happen without the price falling?

Yes. Withdrawing cash, a firm raising its house requirement on a stock, or margin interest growing the loan can all push equity below the requirement while the price stands still.

Summary

A maintenance margin call triggers when equity falls below the maintenance share of market value: 25% under FINRA Rule 4210, often more at your firm. The trigger price is loan ÷ (shares × (1 − m)), and curing a deficiency by selling takes deficiency ÷ m of stock. Reg T calls are a separate demand for the initial 50% on new purchases, due within one payment period and subject to mandatory liquidation if unmet. FINRA is clear that a firm can sell your securities without notice and in the order it chooses, so the time to know your call price is before you borrow, not after the price gets there.