Stock Margin Calculator
Position, loan and equity, with the call price attached.
Work out Stock Margin. Position, loan and equity, with the call price attached. Shows the price the call arrives at, not just today's position.
Reg T's floor is 50%. Your broker may require more.
FINRA's floor is 25%. Brokers commonly require 30–40%, more on volatile names.
Leverage
2.00×
$10,000 of equity holding $20,000
Equity moves with the whole $20,000 while your $10,000 stays fixed, which is exactly why the percentage return is multiplied by 2.00. A 50% fall removes the stake entirely, and the call arrives well before that, at $66.67.
How the Stock Margin Calculator works
One identity carries the whole of brokerage margin: equity equals market value less the loan. Everything else — leverage, the initial requirement, the price a call arrives at — is that expression rearranged. This lays the position out so those quantities are visible together rather than scattered across a statement.
Also known as: margin trading calculator · brokerage margin calculator · equity margin calculator · margin account calculator · share margin calculator
The calculation itself
One identity carries all of it: equity = market value − loan. Leverage is market value divided by equity. The initial requirement caps how large a position a given amount of cash can open.
Everything else in this cluster is that expression rearranged. The call price solves it for price; buying power solves it for market value; the wipeout move solves it for the fall that takes equity to zero.
The loan is fixed in dollars while the position moves. That asymmetry is the entire source of leverage's effect.
In practice
$10,000 of cash buying 200 shares at $100 gives a $20,000 position and a $10,000 loan — exactly 2:1, which is the maximum Regulation T allows at its 50% floor.
A 10% rise takes the position to $22,000. The loan is still $10,000, so equity is $12,000: a 20% return on the cash. The whole gain accrues to you because the lender's claim is fixed.
A 10% fall works identically in reverse, leaving $8,000 of equity — down 20%. And a 50% fall leaves $10,000 of position against a $10,000 loan: equity is zero.
The margin call arrives well before that. At a 25% requirement it comes at $66.67, a 33.3% fall, which is the number that actually governs how much decline the position can survive.
Where the figure deceives
Leverage is usually described as amplifying returns, which is true and incomplete. It amplifies the percentage move in both directions, but only the downside has an absolute floor — you can lose the entire stake and there is no mirror-image outcome on the upside at the same distance.
Interest is invisible in the position and real in the account. It accrues daily whether the position rises or falls, and on a long hold it can exceed the gain entirely.
And the requirement is checked continuously, not at purchase. A position opened at exactly the initial requirement is immediately at risk from any decline, because the maintenance test starts applying the moment the trade settles.
Acting on it
Work out the call price and the wipeout move before opening, and decide whether you could hold through both. If the answer is no at the size you were considering, the size is the thing to change.
Leave room between what you may borrow and what you do. Buying power is a regulatory ceiling, not a target.
Price the interest across the holding period you actually intend, not the one you hope for.
Not financial advice. This calculator is for planning and illustration, not financial advice. Real products carry fees, taxes, and terms it does not model. Confirm figures with your lender or a qualified adviser before committing.
Frequently asked questions
How does buying stock on margin work?
You put up part of the purchase and the broker lends the rest against the securities as collateral. Regulation T caps the loan at half the purchase for most stocks, so $10,000 of cash buys $20,000 of stock.
What is my equity in a margin position?
Market value less the loan. It moves with the full position while your contribution stays fixed, which is exactly why leverage amplifies the percentage return in both directions.
What happens if the stock rises?
The loan stays flat and the gain is entirely yours, so a 10% rise on a 2:1 position is a 20% return on equity before interest. That asymmetry is the appeal, and it works identically in reverse.
Is margin the same as a leveraged ETF?
No. A leveraged ETF rebalances daily, which decays returns over time in a way a margin loan does not. A margin position carries interest and a call risk instead. Different mechanisms and different failure modes.
Do I pay interest on the loan?
Yes, accrued daily for as long as the loan is outstanding. It is charged whether the position rises or falls, and on a long hold it can exceed the gain — the break-even move is worth calculating before opening the position.
Put this calculator on your own site
Free to use, on any site, commercial or not. Paste this where you want it to appear. It is a plain iframe, so it works in WordPress, Squarespace, Wix, Webflow, Ghost and anything else that accepts HTML.
<iframe src="https://www.thecalclibrary.com/embed/stock-margin-calculator" width="100%" height="640" style="border:1px solid #e2e8f0;border-radius:12px" loading="lazy" title="Stock Margin Calculator"></iframe>The only condition is that the credit line stays visible. It sits inside the frame, so you do not have to do anything to keep it.