U.S. · Trading
Margin interest calculator.
Daily, monthly and yearly interest on a margin loan, plus equity, the price drop to a maintenance call and the return you need to cover it.
Your numbers
Result
Margin interest is the quiet cost of borrowing to invest: it accrues every day and is posted to your account, whether the trade works or not. This calculator turns a loan balance and rate into cost per day, per month and per year, handles a two-tier rate schedule, and shows the other number margin borrowers need, which is how far the position can fall before the broker asks for more money.
How this is calculated
Interest per day is the balance times the annual rate divided by the days in the broker's year. Brokers do not all say the same thing: Fidelity's margin page says interest is charged daily on settled debit balances, with the rate set by a schedule based on the average daily debit balance; Interactive Brokers says it accrues interest daily on a benchmark-plus-spread basis, with tiers applied to slices of the balance and posted monthly; Schwab says interest accrues daily and is posted monthly. None of those pages states the day-count, so the tool lets you choose a 360- or 365-day year. The tool does not supply rates; it uses the one you type.
For the risk figures it uses the rules around the loan. Regulation T (12 CFR 220.12) requires 50 percent of the current market value as margin for a margin equity security, so equity below 50 percent of the position is flagged. FINRA Rule 4210 sets a maintenance margin of 25 percent of the current market value of the margin securities held long. If equity is value minus loan, the call happens when (value - loan) / value falls to the maintenance level, so the drop to a call is 1 - loan / ((1 - maintenance) x value). As of 2026-10-26 those two figures are from the eCFR text and FINRA's rulebook, and your broker can require more.
Interest paid on a margin loan used to buy investments is investment interest. IRS Topic 505 says investment interest is deductible as an itemized deduction but limited to your net investment income; Publication 550 covers the limit and Form 4952.
Worked examples (hypothetical figures, real arithmetic)
One rate. You borrow $25,000 at 10% on a 360-day basis. Interest is $25,000 x 10% / 360 = $6.94 a day, $208.33 for 30 days, $2,500.00 over a 360-day year. The same loan on a 365-day basis costs $205.48 for 30 days. For the position to just cover the interest it must gain 0.42% in those 30 days.
The maintenance call. The loan sits under a $50,000 position, so your equity is $25,000.00, 50% of the position, exactly the Regulation T 50% starting level. With a 25% maintenance requirement a call comes when the position falls to $25,000 / 0.75 = $33,333, a 33.3% drop.
Two tiers. Borrow $150,000 with the first $100,000 at 8% and the rest at 7%. Daily interest is ($100,000 x 8% + $50,000 x 7%) / 360 = $31.94, so $958.33 for 30 days, a blended rate of 7.67%.
Mistakes people make
- Using the headline rate for the whole loan. Tiered schedules charge less on larger slices, so the blended rate differs.
- Ignoring the day-count. 360 versus 365 changes the cost a little; use your broker's.
- Treating 25% as your call line. Brokers can set higher maintenance requirements, sometimes called house requirements.
- Assuming it is deductible. The deduction is limited to net investment income and only if you itemize.
Who this is for, and what it does not cover
It is for someone using a margin loan to hold long stock. It does not cover short sales, portfolio margin, options margin, interest compounding when interest is added to the loan, changing balances during the period, or any broker's current rates, which you must read from its schedule.
FAQ
How is margin interest calculated?
Balance times the annual rate divided by the days in the broker’s year, accrued daily and posted monthly. Some brokers use a 360-day year and some a 365-day year, so check your margin agreement.
Is there a minimum equity or maintenance level?
Regulation T requires 50 percent of the value as initial margin for most equity purchases. FINRA Rule 4210 sets a 25 percent maintenance margin on long margin securities. Brokers can require more.
How far can my stock fall before a margin call?
With loan L and position value V, the call comes when (V - L) / V reaches the maintenance percent. At 25 percent maintenance the drop is 1 - L / (0.75 x V).
Is margin interest tax deductible?
It can be deducted as investment interest if you itemize, but only up to your net investment income, according to IRS Topic 505 and Publication 550.
Do brokers charge different rates for bigger loans?
Often yes. Interactive Brokers, for example, describes tiers where each slice of the balance pays its own rate. Use the tier boxes to model that.
Does this tool know my broker’s rate?
No. Rates change and differ by account, so the tool uses only the rate you enter from your broker’s schedule.
Sources
Retrieved 2026-10-26. Each link was opened and checked against the claim next to it.
- 12 CFR 220.12, Regulation T margin requirements: 50 percent of current market value for a margin equity security.
- FINRA Rule 4210, Margin Requirements: maintenance margin of 25 percent of the current market value of margin securities held long.
- Fidelity: Margin rates: interest charged daily on settled debit balances; rate set by a schedule based on average daily debit balance.
- Interactive Brokers: Margin rates: interest accrued daily, posted monthly, with tiered balances.
- Charles Schwab: Margin loans: interest accrues daily and is posted monthly.
- IRS Topic no. 505, Interest expense: investment interest is an itemized deduction limited to net investment income; see Publication 550.
Not tax or investment advice
This page is general information, not tax, legal, investment or financial advice. Rules, limits and rates change, and your facts may differ. Trading, options and margin can lose more than you expect. Confirm anything that matters with the IRS, a CPA, an enrolled agent or a registered adviser before you act. Everything runs in your browser; nothing you enter is sent anywhere.
Common mix-ups
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Often assumedMargin interest is always tax deductible, so the real cost of margin is lower than the rate.
What the source saysIRS Topic 505 says investment interest is deductible as an itemized deduction but limited to your net investment income. Without enough investment income, or without itemizing, the deduction may be reduced or unavailable. [1]
Checked against these sources on .