Margin Call Calculator

The price at which the phone rings

Buy something with borrowed money and there is a price below which your broker stops being relaxed about it. This works out where that price is.

Enter what you paid, the margin you put up, and the minimum your broker requires you to keep. It returns the price at which your equity drops to that minimum and a margin call is triggered.

It is a number worth having before you open a position rather than after. The whole difficulty with leverage is that the distance to trouble feels abstract until it is expressed as a price, and then it is often much closer than expected.

Three fields

1. Initial Purchase Price. What you paid. Enter a price per share and you get a price per share back. Enter the total value of the position and you get the total value at which the call triggers. The arithmetic works either way, so pick whichever you think in.
2. Initial Margin. The percentage of the purchase you funded yourself, rather than borrowed. Put up half and this is 50.
3. Maintenance Margin. The minimum percentage of the position's current value that your equity must stay above. Your broker sets this.

Press Calculate and you get the margin call price.

Both percentages describe equity as a share of position value, and the maintenance figure should be the lower of the two. If it were higher than your initial margin, you would be under call the moment the trade was placed.

Where the formula comes from

The formula looks arbitrary until you build it, and building it explains the whole mechanism.

Margin call price = P × (1 - initial margin) ÷ (1 - maintenance margin)

Start with what happens when you buy on margin at price P with an initial margin of m.

• Your own money in the position: P × m
• Borrowed from the broker: P × (1 - m)

Now the price falls to some level X. Two things happen, and only one of them is what people expect.

The position is now worth X. But the loan is still P × (1 - m). Debt does not shrink when prices do. Your equity is whatever is left after the loan: X minus P(1 - m).

Your broker requires that equity be at least the maintenance percentage of the current value:

(X - P(1 - m)) ÷ X ≥ maintenance margin

Rearrange for X and the formula falls out. The call arrives when X drops to P(1 - m) divided by (1 - maintenance margin).

The important line in all of that is the one about the loan not moving. Your borrowing is fixed in money terms while your position is not, so every unit the price falls comes entirely out of your equity rather than being shared with the lender. That asymmetry is what leverage is, and it is why the losses arrive faster than the gains did.

The textbook case, and the tool's own defaults

A standard US equity purchase. Buy at 100 with 50 percent initial margin and a 25 percent maintenance requirement.

Call price = 100 × 0.50 ÷ 0.75 = 66.67

So the stock can fall 33.33 percent before you hear from anyone. That is a reasonable cushion, and it is roughly what the US regulatory floor is designed to give you.

Now the values the tool starts with. A position of 1,000 with 10 percent initial margin and 5 percent maintenance.

Call price = 1,000 × 0.90 ÷ 0.95 = 947.37

A fall of 5.26 percent and you are called.

Those default numbers describe ten to one leverage, which is contract for difference and foreign exchange territory rather than share dealing. A five percent move is an ordinary week in most markets and an ordinary hour in some. If those are your numbers, the cushion is not really a cushion.

Leverage decides how much room you have

Initial margin and leverage are the same fact stated two ways. Put up 50 percent and you are levered two to one. Put up 10 percent and you are levered ten to one.

Here is what that does to your room to move, with the maintenance requirement set at half the initial margin in each case:

Doubling the leverage roughly halves the distance to a call. At fifty to one, a one percent move against you is the end of the position.

The other variable matters too, and it moves faster than people expect. Hold the maintenance requirement at 25 percent and vary only what you put in:

Notice the last row. When your initial margin equals the maintenance requirement, the call price equals your purchase price. You are at the threshold from the first second, and any fall at all triggers a call. That is the arithmetic explaining why brokers insist the initial requirement sits well above the maintenance one.

What the two percentages should actually be

Do not guess these. They are set by rule and by your broker, and the difference between the regulatory floor and what your broker actually applies is often substantial.

For US listed equities:

Initial margin is 50 percent, set by the Federal Reserve's Regulation T. A broker may lend you up to half the purchase price of a marginable equity security, so you fund at least the other half.

Maintenance margin is 25 percent, set by FINRA Rule 4210 for long positions in margin securities. If your equity falls below a quarter of the current market value, the broker is required to call.

Two things about those numbers that matter more than the numbers.

Your broker can require more, and usually does. Thirty to forty percent maintenance is common, and concentrated positions, leveraged exchange traded products and thinly traded stocks routinely attract far higher requirements. The regulatory 25 percent is a floor, not a description of your account.

Your broker can raise the requirement at any time, on any position, without notice. This is the part that catches people, because it means the call price you calculated on the day you opened the trade is not fixed. In a falling or volatile market, requirements go up precisely when your equity is going down.

Short positions work differently again, with a 30 percent maintenance requirement rather than 25, reflecting that a short can lose more than the position is worth.

Outside US equities the numbers change entirely. Futures margins are set by the exchange and move with volatility. Retail contract for difference and foreign exchange leverage is capped by regulators in many jurisdictions, and the caps vary by instrument and by where you are. Get your actual figures from your actual broker rather than from any table, including this one.

This is a long position formula

The derivation above assumed you bought something and it fell. That is a long position, and the formula belongs to it.

A short position inverts the danger. You borrowed shares and sold them, so you are hurt when the price rises, and your call comes from above rather than below. The relationship between the numbers is different, the maintenance requirement is typically higher, and the loss is not bounded, since there is no ceiling on how far a price can climb.

Do not run a short through this and read the answer as a floor. It is not measuring your risk.

Two other cases where the number here is only a starting point. If you hold several positions in one margin account, the call is assessed on the account as a whole rather than position by position, so a gain elsewhere can offset a fall here. And if you add money or reduce the position, everything recalculates from the new figures.

What a margin call actually is

Worth being clear about the mechanics, because the phrase carries a lot of drama and the reality is more procedural and, in one respect, worse.

A margin call is a demand to restore your equity to the required level. You can meet it by depositing money, by depositing eligible securities, or by closing part of the position to reduce the borrowing.

The part people do not expect is what happens if you do not. Your broker can sell your positions to bring the account back into line, and the terms you agreed to when you opened the account generally allow them to do so without contacting you first, to sell whichever holdings they choose rather than the ones you would have picked, and to do it at whatever price the market offers at that moment.

Which tends to be the worst moment. Forced selling happens when prices are falling, so the sale crystallises a loss at close to the bottom of the move, and you no longer hold the position if it recovers.

Two habits that follow from the arithmetic on this page.

Work out your call price before you open the position, not after. If the distance to it is smaller than a normal move in that instrument, the position is too large.

And leave a buffer rather than sizing to the limit. A position that triggers a call on a five percent move will trigger it, because five percent moves are not unusual. Sizing so that the call price sits outside the range you would expect in ordinary conditions is the difference between a trade that has room to be wrong for a while and one that does not.

This is a planning estimate rather than a statement of your broker's requirements, and nothing here is investment advice. Trading on margin can lose you more than you deposited.

Questions people ask

How is the margin call price calculated?

Purchase price multiplied by one minus the initial margin, divided by one minus the maintenance margin. At 100 with 50 percent initial and 25 percent maintenance, that gives 66.67.

Why does the loan amount matter so much?

Because it does not change when the price does. The position falls in value while the borrowing stays fixed, so the entire fall comes out of your equity rather than being shared with the lender.

What percentages should I enter?

For US equities the regulatory figures are 50 percent initial under Regulation T and 25 percent maintenance under FINRA Rule 4210. Your broker may require more, often 30 to 40 percent maintenance, so use their figures rather than the floor.

Can my broker change the requirement after I buy?

Yes, at any time, on any position, generally without notice. Requirements tend to rise in volatile markets, which is exactly when your equity is under pressure.

Do I enter a price per share or the whole position?

Either. The formula scales, so a price per share returns a price per share and a position value returns a position value.

Does this work for short positions?

No. This is a long position formula, where the danger is a falling price. Shorts are called when the price rises, carry a higher maintenance requirement, and have no upper bound on the loss.

How much can the price fall before I am called?

It depends almost entirely on leverage. At two to one you can absorb a third. At ten to one, about five percent. At fifty to one, about one percent.

What happens if I cannot meet a call?

Your broker can liquidate positions to restore the required equity, typically without contacting you first and without letting you choose which holdings are sold. That selling happens while prices are falling, which locks in the loss.

References

The initial margin requirement of 50 percent for listed equity securities is set by the Federal Reserve Board's Regulation T at 12 CFR 220.12(a). The maintenance margin requirement of 25 percent of current market value for margin securities held long, and 30 percent for short positions, is set by FINRA Rule 4210, which also requires the broker to call for additional collateral when an account falls into margin deficiency. The point that member firms commonly impose requirements above the regulatory floor, and may raise them on leveraged and concentrated positions, follows FINRA's published interpretations of that rule.

1. Financial Industry Regulatory Authority, FINRA Rule 4210: Margin Requirements. https://www.finra.org/rules-guidance/rulebooks/finra-rules/4210
2. Financial Industry Regulatory Authority, Margin Regulation: Key Topics. https://www.finra.org/rules-guidance/key-topics/margin-accounts
3. Financial Industry Regulatory Authority, Interpretations of Rule 4210. https://www.finra.org/rules-guidance/guidance/interps-4210
4. Securities and Exchange Commission, Order Approving a Proposed Rule Change Relating to FINRA Rule 4210 (Margin Requirements), Federal Register, 14 March 2024, citing Regulation T at 12 CFR 220.12(a). https://www.federalregister.gov/documents/2024/03/14/2024-05363/self-regulatory-organizations-financial-industry-regulatory-authority-inc-order-approving-a-proposed