Buying Power Calculator
What the cash supports, at the requirement your broker sets.
Work out Buying Power. What the cash supports, at the requirement your broker sets. Free, with no account and no broker login.
Reg T's floor is 50%. Your broker may require more.
Brokers apply house requirements above the regulatory floor, exclude some securities from margin entirely, and treat day-trading accounts under separate rules this does not model. Your actual buying power will often be lower than this.
Buying power
$20,000
2.00× your cash at 50%
At 50% this cash supports $20,000, borrowing $10,000. That is a ceiling set by regulation, not a recommendation — using all of it leaves no cushion, and the requirement is checked continuously rather than only at purchase. A position opened at exactly this limit is one ordinary down day from a call.
How the Buying Power Calculator works
Buying power is cash divided by the initial margin requirement. At Regulation T's 50% floor that is twice the cash, which is where the familiar two-to-one comes from. It is a ceiling imposed by regulation rather than a recommendation, and the distance between what you may borrow and what you should is the entire subject.
Also known as: margin buying power calculator · initial margin calculator · Reg T buying power · required margin calculator
The calculation itself
Buying power is cash divided by the initial margin requirement. At Regulation T's 50% floor that is twice the cash; at a 30% house requirement it would be 3.33 times.
The borrowed portion is the buying power less the cash. The resulting leverage is one divided by the requirement.
Being a ceiling set by regulation, it says what is permitted rather than what is sensible — and the distance between those two is the whole subject.
In practice
$10,000 of cash at a 50% requirement supports $20,000 of stock, borrowing $10,000. That is the familiar 2:1.
Drop the requirement to 25% and the same cash supports $40,000 at 4:1 — and a 25% fall then removes the entire stake rather than a 50% one. Halving the requirement doubles the position and halves the move that ruins you.
Raise it to 100% and buying power equals the cash: no borrowing, no leverage, no call.
Where the figure deceives
Real buying power is usually lower than the formula. Brokers apply house requirements above the floor, exclude some securities from margin entirely, and impose concentration limits that bite before the headline requirement does.
It also moves during the day with the value of everything in the account. Buying power on a portfolio that has fallen since the morning is smaller — which means it contracts precisely when a falling market makes using it most tempting.
Day-trading accounts operate under separate rules, including a pattern day trader designation with its own minimum equity and its own buying power arithmetic. None of that is modelled here.
And using the full amount leaves nothing for a call. The requirement is tested continuously, so a position opened at the limit is one ordinary down day from needing cash you have already spent.
Acting on it
Ask for the house requirement on the specific security before sizing anything. The regulatory floor is rarely the number that applies.
Size against the fall you could sit through rather than against the maximum permitted.
Keep a cash reserve outside the calculation. Buying power that is fully deployed is a position with no defence.
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 is buying power calculated?
Cash divided by the initial margin requirement. $10,000 at 50% supports $20,000; at a 30% house requirement it would support $33,333. The requirement is set by your broker at or above the regulatory floor.
What is Regulation T?
The Federal Reserve rule capping initial margin for most equities at 50% of the purchase. It is a floor on your contribution, not a ceiling — brokers routinely require more, particularly on volatile or thinly traded names.
Why is my buying power different from this?
Because brokers apply house requirements above the minimum, exclude certain securities from margin entirely, and treat cash and margin buying power differently. Day-trading accounts operate under separate rules this does not model.
Should I use all my buying power?
Using the maximum leaves no cushion, and the requirement is checked continuously rather than at purchase. A position opened at exactly the limit is one ordinary down day from a call.
Does buying power change during the day?
Yes, with the value of everything in the account. Buying power on a portfolio that has fallen since the morning is lower, which is why it contracts precisely when a falling market makes it tempting to buy.
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<iframe src="https://www.thecalclibrary.com/embed/buying-power-calculator" width="100%" height="640" style="border:1px solid #e2e8f0;border-radius:12px" loading="lazy" title="Buying Power 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.