Calculator
Stock Buying Power & Margin Exposure Calculator
The result is a simplified initial-purchase scenario. Broker house requirements, non-marginable securities, existing positions, open orders, options, settlement, and maintenance rules can reduce displayed buying power or cause earlier liquidation.
Buying power is not the same as cash. In a margin account, eligible securities and broker rules can allow a larger initial purchase, but the same leverage magnifies losses and can lead to forced liquidation. Enter available cash, the broker's initial margin requirement, and a stress decline to estimate maximum initial purchasing power and the equity left after the modeled move.
How this stock buying power & margin exposure calculator works
The calculator divides available cash by the entered initial margin percentage to estimate maximum eligible stock exposure. It treats the difference as borrowing, then applies the stress decline to the gross position so the loss is measured against the investor's smaller equity base.
Formula
Maximum initial purchase = cash available ÷ initial margin requirement; equity after stress = cash − maximum purchase × modeled decline
Regulation T permits—but does not require—firms to extend specified credit for eligible securities. Brokers can impose higher house requirements, change them, restrict securities, or liquidate positions under the account agreement. This calculator cannot reproduce a broker's live buying-power engine.
Before you use the result
Assumptions
- • The security is eligible for margin at the entered initial requirement.
- • Cash is fully available and there are no existing positions, orders, unsettled transactions, or account restrictions.
- • The margin loan is unchanged during the modeled price decline and interest, fees, taxes, and slippage are excluded.
Quick start
- 1. Use the initial margin requirement shown by your broker for the specific security, not an assumed universal percentage.
- 2. Compare the maximum purchase with a cash-only purchase to see the leverage created.
- 3. Stress a larger decline and then use the margin-call calculator with the broker's maintenance requirement before placing a trade.
Frequently asked questions
How is stock buying power calculated?
In this simplified initial-margin scenario, available cash is divided by the broker's initial margin percentage. Real buying power also depends on security eligibility, current holdings, open orders, settlement, account type, and house rules.
Does $5,000 always provide $10,000 of buying power?
No. A 50% initial requirement would produce that estimate for an otherwise eligible purchase, but a broker can require more equity or make a security non-marginable.
Is buying power the same as account value?
No. Account value measures current equity or assets. Buying power estimates purchase capacity under account and broker rules and may include borrowing.
Can I lose more than the cash I deposit?
Yes. Leverage magnifies losses, gaps can bypass modeled thresholds, and liquidation proceeds can be insufficient to repay the loan and other obligations.
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