To calculate maintenance margin, take your account’s equity (market value minus what you borrowed) and divide it by the current market value; that percentage has to stay above your broker’s minimum, which under FINRA Rule 4210 cannot be less than 25% for long equity positions but is usually set higher by the firm itself.1FINRA. FINRA Rule 4210 – Margin Requirements Once you know that percentage, one more formula tells you the exact stock price at which your equity would fall to the minimum and trigger a margin call. Everything below walks through both calculations with real numbers.
The Three Numbers You Need First
Every maintenance margin calculation runs on three inputs:
- The current market value of the securities in your margin account. This ticks up and down with the market.
- Your debit balance, which is the amount you borrowed from the broker. You’ll find both figures on the account balances page or your monthly statement, usually under a “margin” or “liabilities” heading.
- Your broker’s maintenance margin requirement, expressed as a percentage. FINRA sets the floor at 25% for long equity positions, but most firms impose “house” requirements in the 30% to 40% range, and some go higher on volatile names. A stable large-cap stock might sit at 30%; a volatile small-cap could be 50% or more. Check your margin agreement for the exact number.1FINRA. FINRA Rule 4210 – Margin Requirements
Two other rules bracket the calculation. You need at least $2,000 (or 100% of the purchase price, whichever is less) to open a margin account.2SEC.gov. Investor Bulletin: Understanding Margin Accounts And under federal Regulation T, the most you can borrow on a new equity purchase is 50% of the purchase price.3eCFR. 12 CFR 220.12 – Supplement: Margin Requirements So on a $20,000 buy, you must put up at least $10,000 in cash. That 50% is the initial margin. The maintenance margin is the ongoing figure you have to watch after the trade settles.
Calculating Your Current Equity Percentage
Equity is what’s left after you subtract the loan from the market value. Express it as a percentage:
Equity percentage = (Market Value − Debit Balance) ÷ Market Value
Say your portfolio is worth $20,000 and you owe $12,000. Your equity is $8,000, and $8,000 ÷ $20,000 = 0.40, or 40%. If your broker’s house requirement is 30%, you have a ten-point cushion. If it’s 40%, you’re on the edge; one bad session could push you under.
Run this at the close each day if you’re carrying a meaningful margin loan. Watching the number trend down over a week is what gives you time to react before the broker does.
Finding the Price That Triggers a Margin Call
Instead of waiting to see how a price move affects your equity percentage, you can solve for the exact stock price at which equity would hit the maintenance minimum. For a single long stock position:
Margin Call Price = Debit Balance ÷ [Number of Shares × (1 − Maintenance Requirement)]
Work it through. You hold 200 shares, you borrowed $12,000, and your broker’s maintenance requirement is 30%.
- Subtract the maintenance requirement from 1: 1 − 0.30 = 0.70.
- Multiply by the number of shares: 200 × 0.70 = 140.
- Divide the debit balance by that result: $12,000 ÷ 140 = $85.71.
At $85.71 per share your account hits the maintenance floor exactly. Market value would be $17,142, equity would be $17,142 − $12,000 = $5,142, and $5,142 ÷ $17,142 = 30%.4Financial Industry Regulatory Authority (FINRA). Know What Triggers a Margin Call Any price below that puts you in call territory.
Treat this number as your early warning line. A price alert or stop-loss set a few dollars above it buys you time to add cash or trim positions on your own schedule. After the broker’s system flags a deficiency, you lose most of that control.
Why Equity Drops Faster Than Price
The debit balance stays fixed (setting interest aside for a moment) while market value shrinks, so the equity percentage falls faster than the price does. A 10% decline in the stock price does not shave 10 points off your equity percentage. Starting at 40% equity, a 10% drop can pull the equity percentage down to about 33%, because the loan hasn’t moved.
To check the formula, plug the margin call price back into the equity calculation: ($85.71 × 200 − $12,000) ÷ ($85.71 × 200). If that equals your maintenance requirement, you did it right.
The Formula for a Short Position
Short sales flip the direction of danger: you’re calling in trouble when the price rises. The trigger price formula becomes:
Margin Call Price = (Short Sale Proceeds + Initial Margin Deposit) ÷ [Number of Shares × (1 + Maintenance Requirement)]
Short 100 shares at $50 with $2,500 of your own money deposited (50% initial margin). Total account assets are $7,500: $5,000 in short sale proceeds plus $2,500. With a 30% maintenance requirement:
- Add the requirement to 1: 1 + 0.30 = 1.30.
- Multiply by shares: 100 × 1.30 = 130.
- Divide total assets by that result: $7,500 ÷ 130 = $57.69.
At $57.69, the shares you owe are worth $5,769, your equity is $7,500 − $5,769 = $1,731, and $1,731 ÷ $5,769 = 30%. Anything above $57.69 triggers a call. The formula uses (1 + requirement) because the short seller’s risk is a rising price, not a falling one.
Adjustments That Change the Requirement
The base formulas assume every share in the account is marginable at a uniform rate. Two situations break that assumption.
Non-Marginable Securities
Stocks trading at $3 or below typically carry a 100% requirement, meaning they have to be paid for entirely in cash. New IPO shares are ineligible for margin for at least 30 calendar days after the offering.5Fidelity Investments. Trading FAQs: Margin If a portion of your portfolio sits in non-marginable positions, your effective borrowing power is smaller than a simple percentage of the total market value implies.
Concentrated Positions
Brokers raise requirements when a single stock dominates. If one position is 60% or more of the marginable value in your account, the maintenance requirement on the entire account can jump to 50%.6Firstrade Securities. Margin Requirements That change moves the margin call price meaningfully closer to where the stock trades today, so re-run the trigger calculation with the new percentage if you’re near the concentration threshold.
Multiple Holdings
If you hold several securities with different requirements, you need either a weighted-average requirement across the account or a per-position calculation. Most brokers compute a blended requirement internally and post the net surplus or deficit on the balances page. For a diversified account, the broker’s real-time figure is more reliable than adding up individual estimates.
How Margin Interest Moves the Trigger Price
Margin interest is easy to forget because it accrues quietly, but it works against your equity every day. Interest compounds daily and posts to the account monthly.7Charles Schwab. What to Know About Margin Each monthly charge grows the debit balance, which lowers equity and pushes the margin call trigger price higher.
Rates typically use a base rate (tied to something like the prime rate or federal funds rate) plus or minus a spread that varies with loan size. Smaller balances pay the highest rates. As of late 2025, effective rates at major brokerages ran from roughly 6% for balances of $50 million and above to over 10% for balances under $100,000. A $50,000 loan at 10.7% costs about $5,350 a year in interest alone.
If you’re carrying a margin loan for weeks or months rather than days, recalculate the trigger price on a schedule. The formula stays the same; the debit balance goes in higher each time, and the price at which a call hits creeps up along with it.
Reading These Numbers on Your Broker’s Platform
You don’t have to run this math from scratch every day. Every major brokerage displays the relevant fields in real time on the account summary or balances page:
- Margin equity: your ownership stake after subtracting the loan. That’s the numerator in the equity percentage calculation.
- Maintenance excess (sometimes called house surplus): the dollar amount by which your equity exceeds the minimum requirement. When it reaches zero, a call is imminent.8Fidelity. Additional Balances
- Buying power: how much more stock you could purchase given current equity. Useful when adding positions, less relevant during a drawdown.
Many platforms include a “what-if” margin calculator that lets you simulate a price drop and see the effect on maintenance excess. Those tools apply each security’s specific requirement automatically, which is more reliable than running the algebra by hand on a diversified account. Use them before adding to a position, not only after the price starts moving against you.
The dashboard will also distinguish a “house call” from a “federal call” (also called an exchange call). A house call means equity fell below the broker’s internal requirement. A federal or exchange call means the regulatory minimum has been breached, which is the more serious of the two.9Vanguard. You Receive a Margin Call – Now What?
One boundary worth noting. Accounts that qualify for portfolio margin (available at $100,000 in equity or more, higher at some firms) don’t use fixed percentage requirements at all. The broker’s risk system prices requirements against the overall position mix, so the formulas above stop applying cleanly. In that setup, the maintenance excess figure the platform produces is the number to watch.