Margin Call Calculator
Find the equity, maintenance requirement, call amount, and the exact price where a long margin position falls short.
What it does
A margin account lets an investor buy more stock than their cash by borrowing the rest from the broker. The broker holds the position as collateral and sets two guardrails: the initial margin at purchase and the maintenance margin that must hold afterward.
Equity is what the position is worth minus the loan. If $10,000 of stock was bought with $5,000 of cash at 50% initial margin, the loan is $5,000 and equity tracks the market value minus that loan.
A margin call happens when equity falls below the maintenance requirement, usually 25% of the position value under FINRA rules. At that point the broker demands a deposit, or it can sell shares to restore the balance.
This calculator solves the position in both directions. It shows the current equity, margin percentage, requirement, and any call amount, then inverts the formula to name the exact price per share where the call begins.
That critical price matters because it does not depend on the current quote at all: it is fixed the moment the purchase is made, as long as the loan amount and margin rules stay the same.
How to use
- Enter the number of shares and the price you paid.
- Set the initial margin: 50% is the Regulation T standard for new long purchases.
- Set the maintenance margin: 25% is the FINRA floor, and brokers can require more.
- Enter the current price to see equity, margin percentage, and any call amount.
- Read the call price per share, the level where the requirement is exactly met.
- Check your broker's actual requirements; house rules and concentrated positions can raise them.
Formula
- Loan
- The borrowed part of the purchase, fixed at the time of the trade.
- Equity
- Position value minus the loan.
- Call price
- The share price where equity equals the maintenance requirement.
The maintenance test compares equity against a percentage of the current position value, not the purchase price, so the bar falls as the stock falls, but the equity falls faster. The call price solves equity = maintenance margin x position value for price, which gives loan / (shares x (1 - maintenance margin)). Below that price a deposit or a sale is needed; margin interest accrues separately and is not included in these figures.
Worked example
Example: 200 shares bought at $50, now $30
200 shares, $50 paid, 50% initial, 25% maintenance, now $30 (defaults).
- Loan at purchase: 200 x 50 x 50% = $5,000.
- Position now: 200 x 30 = $6,000. Equity: 6,000 - 5,000 = $1,000.
- Maintenance requirement: 25% x 6,000 = $1,500.
- Equity is $500 below the requirement, so the call amount is $500. Current margin: 16.7%.
- Call price: 5,000 / (200 x 75%) = $33.33 per share; below that the account falls short.
Reference table
| Price | Equity | Margin | Call |
|---|---|---|---|
| $50 | $5,000 | 50.0% | $0 |
| $40 | $3,000 | 37.5% | $0 |
| $33.33 | $1,666.67 | 25.0% | $0 |
| $30 | $1,000 | 16.7% | $500 |
| $25 | $0 | 0.0% | $1,250 |
| $20 | -$1,000 | -25.0% | $2,000 |
Limits
- Long stock positions only; short sales run the math in the other direction.
- Margin interest, commissions, and dividends are not included.
- Brokers can set higher house requirements and special rules for concentrated positions.
- Portfolio margin accounts use a different risk model entirely, not a flat 25%.
- The call price assumes the loan never changes; paying down the loan rebuilds the cushion.
Common mistakes
- Setting maintenance margin below the broker's real requirement and understating the call.
- Forgetting that the call is a demand for equity, not an automatic sale at the critical price.
- Ignoring margin interest, which grows the loan and raises the call price over time.
- Treating 25% as universal when many brokers require 30% to 40% on volatile stocks.
- Adding to the position on margin after a call, which deepens the hole instead of filling it.
Try it yourself
Quick checks. Answers sit tucked under each question.
100 shares at $80 with 50% initial, now $60, 25% maintenance?
Loan $4,000; equity $2,000; requirement $1,500; no call. Call price $53.33.
500 shares at $20, now $12?
Loan $5,000; equity $1,000; requirement $1,500; call of $500. Call price $13.33.
200 shares at $50, now $30, but maintenance is 30%?
Requirement rises to $1,800, so the call becomes $800; the call price moves to $35.71.
Questions
What triggers a margin call?
Equity falling below the maintenance requirement, usually 25% of the position value at the FINRA floor. The broker sends a demand to deposit funds or sell positions.
How long do I have to meet a call?
Brokers typically give a few business days, but they can liquidate sooner in fast markets. The account agreement sets the terms.
Why is the call amount bigger than the shortfall?
It is not in this model: the call equals the shortfall under the maintenance test. Some brokers may demand enough to climb back to the initial margin, which is larger.
What is Regulation T?
The Federal Reserve rule that sets the initial margin for new purchases, generally 50% of the purchase price for long stock.
Does the call price change over time?
The raw formula stays fixed, but margin interest grows the loan, which raises the call price slightly as time passes.
Can a broker raise my maintenance requirement?
Yes. House requirements start at the FINRA floor and go up, especially for volatile or concentrated positions, and changes take effect immediately.
Sources
- FINRA Rule 4210: margin requirements, 25% maintenance floor
- 12 CFR 220.12: Regulation T initial margin requirements