Margin Calculator

Frequently Asked Questions

How does margin buying power work?

Reg T allows initial margin of 50%; $10,000 of cash supports $20,000 of stock purchases. Maintenance margin is typically 25-30%; falling below triggers a margin call requiring additional cash or forced sale.

What does margin cost?

Broker margin rates in 2025 typically range from about 5% (large balances at IBKR) to 13%+ (retail brokers, smaller balances). Margin interest is tax-deductible against investment income with limitations.

What are the risks?

Margin amplifies both gains and losses. A 50% drop in a fully-margined position wipes you out. Forced liquidations during a panic often happen at the worst possible prices. Most retail investors should avoid more than 10-20% leverage.

Is portfolio margin different?

Yes; portfolio margin uses risk-based calculations (often 15% margin on diversified portfolios, vs. 50% Reg T). It requires $100,000+ accounts and an application. It allows much larger leverage but with the same amplified risk.

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Investment Disclaimer: Estimates only. Not investment advice.

This calculator provides estimates for educational purposes only and is not investment advice. Past performance does not guarantee future results. Consult with a qualified financial advisor before making investment decisions. All investments carry risk, including potential loss of principal.

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How This Calculator Works

You enter your cash equity, the initial and maintenance margin percentages, the share price and number of shares, your broker's margin interest rate, a holding period, and a stress-test price drop. From these the tool derives your maximum buying power, the size of the margin loan you would take on, your equity percentage, and the critical margin call price - the level at which equity falls below the maintenance threshold and the broker demands more cash. It also computes the dollar interest cost over your holding period and runs a stress test showing whether the chosen price decline would trigger a call. A warning fires if your position exceeds available buying power.

Formulas Used

Buying power = cash ÷ initial margin%, so at the Reg T standard of 50% your buying power is twice your cash. Margin loan = position value − cash; equity% = (position − loan) ÷ position. A call triggers when (position − loan) ÷ position < maintenance%, which rearranges to a call price of loan ÷ (shares × (1 − maintenance%)). Interest = loan × rate × (days ÷ 365). The stress test re-prices the position at (1 − drop%) and re-checks the equity ratio.

Worked Example

With $25,000 cash, 50% initial margin gives $50,000 of buying power. Buy 500 shares at $100 ($50,000): the loan is $25,000 and equity is 50%. At a 30% maintenance requirement, the call price = 25,000 ÷ (500 × 0.70) ≈ $71.43, so the stock can fall about 28.6% before a call. Borrowing $25,000 at 11% for 90 days costs roughly $678 in interest. A 20% stress drop takes the price to $80 and equity to about 37.5% - still above 30%, so no call - but a 30% drop would breach it.

Common Mistakes

Maxing out buying power and leaving no cushion - a modest dip then triggers a forced sale at the worst time.

Forgetting that margin amplifies losses at the same rate as gains; 2× leverage doubles a drawdown.

Overlooking interest, which accrues daily and quietly erodes returns.

Assuming the maintenance requirement is fixed - brokers can raise it unilaterally on volatile names, tightening the call price without warning.

Tips & FAQ

Reg T (the Federal Reserve's Regulation T) sets initial margin at 50%; FINRA Rule 4210 sets the maintenance minimum at 25%, though brokers commonly require 30–40%. 2025 retail margin rates range from roughly 5.8% at Interactive Brokers to 11–14% at full-service brokers. Best practice is to keep a 30%+ cushion above the call price, avoid margin on single volatile positions, and compute the call price before opening a trade. Pattern day-trading rules require a $25,000 minimum equity. Educational only, not investment advice.

Frequently Asked Questions

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