How margin interest is charged
Margin interest accrues daily on your debit balance, the amount you have borrowed, and is usually billed monthly. The interest for a period is the balance times the annual rate times the days, divided by the days in the interest year.
Omni Calculator's margin interest formula divides by 360, and so does this page by default. Other brokers use 365, and your margin agreement decides, so you can switch the day count.
Worked example: published margin interest cases
Omni Calculator's example is $3,000 at 5% for 30 days, which costs $12.50. The same page shows $5,000 for 10 days at 5% costing $6.94.
On a $50,000 balance at 8% for 30 days, the interest is $333.33, or $11.11 a day. On a 365-day year the same loan costs $328.77. Over a full 365-day year, a 360-day basis charges more than the stated rate: $10,000 at 6% costs $608.33, which is 6.08%.
Tiered margin rates
Many brokers charge a lower rate as the balance grows. Interactive Brokers' published USD table for IBKR Pro, as we read it on 26 October 2026, showed 5.380% up to 100,000 and 4.880% from 100,000 to 1,000,000. The page says it blends the tiers, charging each slice at its own rate. Rates move with the benchmark, so check the broker's page and type in the current figures.
On a $150,000 balance with those two tiers, blended interest is $7,820.00 a year, which is 5.21% on the whole balance. That is $651.67 for 30 days on a 360-day year, or $642.74 on 365. If the whole balance were charged at the second tier's 4.88%, 30 days would cost $610.00. Not every broker says which method it uses, so the calculator offers both and labels the one you choose.
The margin call price
Your broker sets a maintenance margin, the least equity share it requires. A margin call happens when the portfolio falls to the loan divided by one minus that share. For a $50,000 loan and a 30% maintenance margin, that is $71,428.57, so a $100,000 portfolio is $28,571.43 above the level and would need to fall 28.57% to trigger a call.
Hold 1,000 shares of one stock and a 25% maintenance margin on a $50,000 loan, and the call price is $66.67 a share. This page does not quote a required minimum: enter the figure from your own broker, because firms can set requirements above any general rule.
Taxes and what is left out
This page does not include tax. It also leaves out compounding of posted interest, margin requirements on individual positions and trading fees. A margin loan is a demand loan, so your broker can ask for more money or sell holdings if the account falls.
For the investment interest deduction, use the margin interest tax deduction calculator.
Use the right country page
UK investors use different terms and a different day count.
For the UK, open the UK margin loan interest calculator.
For any currency, use the margin loan interest calculator.
Inputs for the US margin loan interest calculator
Days in the interest year
The divisor for the daily rate, 360 or 365. Your margin agreement says which.
Rate tiers
One rate, or two or three tiers by balance. With tiers, choose blended or whole balance and enter each tier's limit and rate.
Margin loan balance
How much you owe the broker, assumed level for the whole period.
Margin interest rate (per year)
The annual rate your broker charges. With tiers, this is the rate on the first tier.
Days borrowed
How many days you hold the loan.
Portfolio value
The market value of everything held in the account, used for the margin call level.
Maintenance margin
The least equity share your broker requires. Brokers set their own, so check yours.
Shares held in one stock (optional)
To see a margin call price per share. Enter 0 to skip.
CALCULATOR QUESTIONS
US margin loan interest calculator questions
How do you calculate margin interest?
Multiply the balance by the annual rate and the days, then divide by 360 or 365. On $3,000 at 5%, 30 days cost $12.50 on a 360-day year.
Do brokers use 360 or 365 days?
Both are used. Omni Calculator's formula uses 360. Check your margin agreement and set the day count to match.
Are margin rates tiered by balance?
Often. Interactive Brokers says it blends its tiers. Other brokers may charge the whole balance at one tier's rate, so check how yours applies them.
How do I find my margin call price?
Divide your loan by one minus your broker's maintenance margin, then by your shares. A $50,000 loan, 25% margin and 1,000 shares gives $66.67.
Is margin interest tax deductible?
This page does not work out tax. The margin interest tax deduction calculator covers the US treatment.