Margin interest calculator
Turn amount borrowed, the broker's quoted annual rate, and a holding period into one dollar figure, and see how sensitive that figure is to rate and to time.
Worked example — Interest cost over 90 days: $1,479.45. $50,000 borrowed at 12% per year, $16.44 a day
90-day hold at 12%: The page's own default and worked-example scenario.
Typical retail margin rates run roughly 6% to 14% depending on balance tier, as a general anchor, not any one broker's quote.
Brokers usually compound monthly and can change the rate without notice, and a margin call can force you to add cash or sell while the loan is outstanding.
Real margin accounts charge on the average daily balance and usually price the rate as a base rate plus a spread that can float with the broker's cost of funds, so treat a quoted rate as an estimate for the period rather than a locked number. This calculator charges the full period at a simple daily rate with no compounding inside the period; brokers that compound monthly add a small amount on top, growing with the term. The loan is secured by your securities: if the account falls below the maintenance requirement, the broker can force a sale to bring it back, at whatever the market is doing at that moment.
Interest cost by holding period
| Holding period | Interest cost | Total to repay |
|---|---|---|
| 7 days | $115.07 | $50,115.07 |
| 30 days | $493.15 | $50,493.15 |
| 90 days | $1,479.45 | $51,479.45 |
| 180 days | $2,958.90 | $52,958.90 |
| 365 days | $6,000.00 | $56,000.00 |
Interest is linear in days: double the holding period and the cost doubles with it. A year-long hold at this rate costs $6,000, exactly the $6,000 annual figure the rate implies, since 365 days is the full year the rate is quoted against.
Your rate vs. two points either side
| Rate | Daily interest | Interest over 90 days |
|---|---|---|
| 12% (entered) | $16.44 | $1,479.45 |
| 10% (-2 pts) | $13.70 | $1,232.88 |
| 14% (+2 pts) | $19.18 | $1,726.03 |
Four points of rate on $50,000 is a $5.48 daily gap, $493.15 over the entered 90-day period. The gap scales with the amount borrowed and the holding period, not with the rate itself, which is why shopping a quote by even a point or two is worth doing on a large or long-held balance.
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Compounding margin models, rate-vs-period comparison tables, margin call stress tests, and after-tax cost estimates are Pro features. The launch list sends one email at launch.