Stock Margin Calculator
Buying stock on margin means the broker lends you part of the purchase price, and this calculator prices that deal: the total position value, the cash you must deposit up front, the amount the broker lends, the minimum equity you must keep, and the buying power your deposit creates. It is the stock brokerage version of margin math under Regulation T and FINRA rules, not the forex leverage formula and not the profit-margin percentage that most pages titled “margin calculator” actually compute.
Maintenance margin here is a dollar figure computed from the purchase value, not a live equity monitor. Brokers measure it against the current market value of your position, which moves every second the market is open.
Quick Answer
Buying 100 shares at $100 with a 50% initial margin and a 25% maintenance margin means a $10000.00 position, $5000.00 of your own cash up front, $5000.00 borrowed from the broker, a $2500.00 maintenance margin floor, a $66.67 margin-call price, and $10000.00 of buying power. The values are pre-filled in the calculator; press Calculate margin to reproduce them exactly.
Key takeaways
- Initial margin is the entry ticket, set by Regulation T at 50% of the purchase price for most U.S. stocks. Maintenance margin is the ongoing floor, with FINRA requiring at least 25% equity in the account.
- The borrowed amount is the position value minus your initial margin; it is the loan that accrues margin interest, which this tool does not compute.
- Buying power in this calculator equals the position value, because the initial margin is derived from the position rather than from cash you already hold. Brokers compute the reverse direction: buying power = your cash divided by the margin requirement.
- A margin call is triggered by price, not by the calculator’s maintenance-margin line. The price that wipes out your cushion is the borrowed amount divided by (1 − maintenance %), which the calculator now reports as its margin-call price line, with the section below working the same arithmetic by hand.
- Quick Answer
- How to use the stock margin calculator
- The margin formulas, and the rules behind the percentages
- Worked example: 100 shares at $100, checked line by line
- What buying power really means here: an honest reading
- The margin call price, worked by hand
- Margin interest and the other things this leaves out
- What competing margin calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use the stock margin calculator
Enter four numbers and click Calculate margin. The results stay hidden until you calculate.
- Stock price: the per-share price you plan to pay, for example 100. It is pre-filled at $100.
- Number of shares: the size of the planned position, pre-filled at 100 shares for a $10,000 total.
- Margin requirement: the initial margin percentage your broker enforces, pre-filled at 50%, the Regulation T minimum for marginable U.S. stocks.
- Maintenance margin: the ongoing minimum, pre-filled at 25%, the FINRA floor. Most brokers set 30% to 40%, so check your firm’s schedule and type its number.
- Read the six lines: total investment, initial margin, borrowed amount, maintenance margin, buying power and margin-call price per share. Use Copy my results or Share results to keep them.
Every field must be a positive number; anything else shows “Please enter valid values for all fields” and keeps the results hidden.
The margin formulas, and the rules behind the percentages
Every margin figure is a percentage of the position value, which is just price times shares. The arithmetic is deliberately simple because the rules are the hard part:
Initial margin = total investment × margin requirement %
Borrowed amount = total investment − initial margin
Maintenance margin = total investment × maintenance margin %
Buying power = initial margin ÷ margin requirement %
Margin call price = borrowed amount ÷ (shares × (1 − maintenance %))
The percentages are not the tool’s choice; they come from the rulebook. The supplement to Regulation T sets the initial margin for margin equity securities at 50% of the security’s market value, and FINRA Rule 4210 requires your equity to stay at or above 25% of the position’s current market value. Two practical refinements from FINRA’s margin accounts guide: most brokers set house requirements above the 25% floor (often 30% to 40%), and FINRA requires at least $2,000 of equity to open a margin account.
Worked example: 100 shares at $100, checked line by line
The pre-filled example runs all six outputs with the Regulation T 50% requirement and the FINRA 25% floor:
Two more real runs of this calculator to check against:
| Inputs | Total | Initial | Borrowed | Maintenance | Buying power | Margin call |
|---|---|---|---|---|---|---|
| $100 × 100, 50% / 25% | $10000.00 | $5000.00 | $5000.00 | $2500.00 | $10000.00 | $66.67 |
| $80 × 200, 40% / 30% | $16000.00 | $6400.00 | $9600.00 | $4800.00 | $16000.00 | $68.57 |
| $45.50 × 50, 50% / 30% | $2275.00 | $1137.50 | $1137.50 | $682.50 | $2275.00 | $32.50 |
What buying power really means here: an honest reading
On the worked example the calculator reports $10,000 of buying power on a $10,000 position, which is the construction, not a coincidence. The tool sizes your initial margin from the position you entered, so dividing that margin back by the requirement returns the position. Real brokers run the formula in the opposite direction: they start from the cash already in your account and divide by the requirement, so $5000.00 of settled cash at a 50% requirement genuinely buys $10000.00 of stock, and $5000.00 at a 60% house requirement buys only $8333.33.
The badge under the results says this out loud each time you calculate, because several rival tools report a buying-power number with no explanation of which direction the math runs. Treat this tool’s buying power as “the position this margin requirement supports”, and use your broker’s own figure, based on your actual account equity, before placing the trade. The distinction also matters for leveraged crypto margin, a separate product with its own isolated and cross-margin rules, covered by the isolated margin calculator rather than this page. Options have their own margin schedule too, which is why the option margin calculator exists alongside this one.
The margin call price, worked by hand
The maintenance margin line ($2,500 on the worked example) is frozen at the purchase price. A real margin call is triggered when your equity, which is market value minus loan, falls below the maintenance percentage of the position’s current market value. The price at which the call arrives is:
On the worked example: $5000.00 ÷ (100 × 0.75) = $66.67 per share. Check it: at $66.67 the position is worth $6666.67, equity is $6666.67 − $5000.00 = $1666.67, and $1666.67 ÷ $6666.67 = 25.00%, exactly the floor. At $70.00 the position is worth $7000.00, equity $2000.00 is 28.6% of market value, so no call; at $60.00, equity is $1000.00 against a $1500.00 floor, and the broker demands cash or starts selling.
Two warnings belong with that number. First, brokers can liquidate without asking: your margin agreement gives them the right to sell your securities to cover a call, with no obligation to contact you first, a point FINRA states explicitly. Second, the calculator now reports this price directly as its margin-call price line; the hand-check above is how you verify it.
Margin interest and the other things this leaves out
The borrowed amount is a loan, and loans charge interest. Margin interest accrues daily on the debit balance and compounds monthly at most brokers, running whether the position rises, falls or sits still, which is why the SEC’s fee guidance treats financing costs as a first-class drag on returns. This calculator has no interest input and no holding period, so it cannot show that drag; use it for the requirement math, then price the carry cost against your broker’s published margin rates, such as the schedules on Schwab’s margin pages.
Three more honest boundaries. The tool models a long stock purchase only: short sales flip the equity math (FINRA’s minimum for shorts is 30%, not 25%) and are not computed here. It assumes one stock and one requirement, so a portfolio with mixed requirements needs your broker’s real-time margin screen, not this page. And leveraged gains are still taxed as capital gains when realized; the IRS rules on capital gains and losses apply to the profit, not to the leverage that produced it. For the profit side of a completed trade, the stock market calculator and the stock sell calculator carry the trade P&L and CAGR arithmetic.
What competing margin calculators miss
Searching “margin calculator” returns at least four different products, and matching the right one to your question matters more than any single feature:
- Correct-intent but thin tools (Brave Calculator’s stock margin page): computes the initial margin from price, shares and a percentage, then stops: no borrowed amount, no maintenance line, no buying power, and none of the Reg T and FINRA rules behind the percentages.
- Margin-call specialists (OnlyCalculators’ margin call tool): the strongest rival for the downside question, with an equity-zone visualization and the exact call price. It does not do the initial margin or buying-power side at all, which is why the two tools complement rather than replace each other.
- Wrong-intent tools (Calculator Doc, Calculator Ultra’s “stock margin” pages): these compute a profit ratio, selling price divided by purchase price times 100, which answers a question a margin trader never asked.
- Wrong-market tools (India MTF calculators, forex margin calculators): the Indian margin-trading-facility tools price daily interest and broker charges under SEBI rules, and forex tools price lot-size leverage. Both are legitimate for their markets and misleading for a U.S. Reg T stock purchase.
- The gap this page fills: the complete six-line Reg T picture in one run, the rules named beside the numbers they produce, an honest account of which direction the buying-power math runs, and the margin-call price computed in the tool and worked by hand with the warning that brokers can liquidate without calling you first.
Frequently asked questions
Under the Federal Reserve’s Regulation T, a broker may lend you at most 50% of the purchase price of a marginable stock, so you must deposit at least 50% yourself. On a $10,000 purchase that is $5,000 of your own money and a $5,000 margin loan. Brokers may set higher house requirements, and some securities cannot be bought on margin at all.
Initial margin is the one-time deposit to open the position; maintenance margin is the ongoing minimum equity you must keep while the position is open. FINRA requires your equity to stay at or above 25% of the position’s current market value, and most brokers enforce 30% to 40%. Fall below it and you face a margin call.
Buying power is the total value of securities you can purchase, combining your cash with the broker’s loan. The standard relationship is buying power = cash deposited divided by the margin requirement, so $5,000 of cash at a 50% requirement supports a $10,000 position. Your broker’s figure is based on your actual account equity and is the one that governs real trades.
Because the tool works from the position you entered rather than from cash you hold: it sizes the initial margin from the position, then divides that margin back by the requirement, which returns the position value. It is the same buying-power relationship read in the opposite direction, and the badge under the results says so explicitly. It tells you what position the requirement supports, not what your account can currently buy.
A margin call is your broker’s demand for more cash or securities when your equity falls below the maintenance requirement. You can meet it by depositing funds, depositing marginable securities, or selling positions. If you do not act, the broker may liquidate your holdings without contacting you first, a right your margin agreement grants them.
Divide the borrowed amount by shares times (1 minus the maintenance percentage). For 100 shares with a $5,000 loan and a 25% maintenance requirement, that is $5,000 divided by (100 times 0.75) = $66.67 per share. At that price your equity is exactly 25% of the position value; below it, the broker can call the loan. The calculator now prints this price directly as its margin-call price line.
No. The borrowed amount is a loan and margin interest accrues daily on it, compounding monthly at most brokers, but this tool has no interest-rate or holding-period input, so it cannot show that cost. Price the carry separately against your broker’s published margin rates.
No, this page models a long stock purchase only. Short sales use different minimums (FINRA’s floor is 30% for shorts) and inverted equity math, while crypto margin products use isolated or cross-margin schemes with liquidation prices rather than Reg T percentages. Use the isolated margin calculator for crypto-style margin and the option margin calculator for options positions.
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References
- Financial Industry Regulatory Authority (FINRA). Margin Accounts. Accessed October 23, 2026.
- Financial Industry Regulatory Authority (FINRA). Rule 4210: Margin Requirements. Accessed October 23, 2026.
- Financial Industry Regulatory Authority (FINRA). Rule 2264: Margin Disclosure Statement. Accessed October 23, 2026.
- Legal Information Institute, Cornell Law School. 12 CFR § 220.12: Supplement: margin requirements (Regulation T). Accessed October 23, 2026.
- Financial Industry Regulatory Authority (FINRA). Margin Statistics. Accessed October 23, 2026.
- Charles Schwab. Margin Loans: Margin Trading Account. Accessed October 23, 2026.
- U.S. Securities and Exchange Commission, Investor.gov. Introduction to Investing: Stocks. Accessed October 23, 2026.
- Financial Industry Regulatory Authority (FINRA). Investing Basics: Stocks. Accessed October 23, 2026.
- U.S. Securities and Exchange Commission, Investor.gov. Understanding Fees. Accessed October 23, 2026.
- Internal Revenue Service. Topic No. 409, Capital Gains and Losses. Accessed October 23, 2026.