Margin Interest Calculator
Daily accrual, and how far the position must rise to cover it.
Work out Margin Interest. Daily accrual, and how far the position must rise to cover it. Built to be checked against your own margin agreement.
From your broker's schedule — rates are tiered and move with the benchmark.
Used for the break-even move.
Interest cost
$66.67
over 30 days at 8%
The position has to gain 0.33% before the borrowing has paid for itself, and that is the number a statement never shows next to the holding. Interest accrues whether the position rises or falls, and over a full year this loan would cost $811.11.
How the Margin Interest Calculator works
Margin interest accrues daily on a 360-day year for as long as the loan is open, whether the position rises or falls. The number worth reading is not the interest itself but the break-even move: how far the position has to gain before the borrowing has paid for itself. On a long hold at a typical rate that figure gets uncomfortable, and it never appears next to the position on a statement.
Also known as: margin loan calculator · stock margin interest calculator · margin lending calculator · margin interest rate calculator · margin loan repayment calculator
The calculation itself
Loan balance times the annual rate, divided by 360, accrued each day the loan is open. The 360-day year is the banker's convention, the same one discount notes use.
The consequence is that a quoted rate understates the annual cost slightly: you are charged 365 days of interest at a rate divided by 360. An 8% quote works out near 8.45% effective.
The figure worth reading, though, is the break-even move — total interest as a share of the position. That is how far the holding must rise before the borrowing has paid for itself.
In practice
A $10,000 loan at 8% accrues $2.22 a day. Over 30 days that is $66.67; over a full year, $811.11.
Against a $20,000 position, thirty days of interest is a 0.33% break-even — trivial. Held for a year it becomes 4.06%, which is no longer trivial: the position must rise more than four percent before the leverage has earned anything.
Measured against your own $10,000 of equity rather than the position, that year of interest is 8.11% — the cost of the borrowing expressed as a drag on the capital actually at risk.
None of this appears beside the holding on a statement. Interest is reported separately, as an account charge, which is precisely why the break-even move is worth calculating deliberately.
Where the figure deceives
Rates are tiered by balance and vary widely between brokers — large loans pay materially less than small ones, and the spread between the cheapest and dearest brokers is measured in whole percentage points rather than basis points.
Unpaid interest is generally added to the loan, so it compounds. On a position held for years without paydown, the loan grows on its own and takes the call price up with it.
The rate is also not fixed. It moves with the benchmark, usually without notice, which makes a long-held margin position a floating-rate liability against a volatile asset.
This assumes a constant balance. Adding to or paying down the loan changes the daily accrual from that day forward, so a real statement will not match a single-balance calculation.
Acting on it
Calculate the break-even move over the period you actually intend to hold, and compare it against what you expect the position to do. If they are close, the leverage is not earning its keep.
Compare broker rates before assuming they are similar. On a large balance the difference is worth more than most trading edges.
Pay the interest rather than letting it capitalise, if the account allows it. Compounding on a loan secured against a falling asset is the worst version of this arrangement.
Not financial advice. This calculator is for planning and illustration, not financial advice. Real products carry fees, taxes, and terms it does not model. Confirm figures with your lender or a qualified adviser before committing.
Frequently asked questions
How is margin interest calculated?
Loan balance times the annual rate, divided by 360, accrued each day the loan is outstanding. $10,000 at 8% costs about $2.22 a day, or $66.67 over thirty days.
What rate will I pay?
It depends on the broker and on the size of the loan — rates are tiered, with large balances paying materially less. They move with the benchmark, so this takes the rate as an input rather than quoting one that would be stale within weeks.
Why a 360-day year?
It is the banker's convention, and it makes the effective annual cost slightly higher than the quoted rate because you are charged 365 days of interest on a rate divided by 360.
Is margin interest tax deductible?
In the US, investment interest expense may be deductible against investment income if you itemise, with limits and carryforward rules. It is genuinely situation-specific, so treat that as a question for a tax adviser rather than a calculator.
Does the interest compound?
Unpaid interest is generally added to the loan balance, so subsequent interest accrues on it. On a position held for years without paydown, that compounding is a meaningful part of the total cost.
Put this calculator on your own site
Free to use, on any site, commercial or not. Paste this where you want it to appear. It is a plain iframe, so it works in WordPress, Squarespace, Wix, Webflow, Ghost and anything else that accepts HTML.
<iframe src="https://www.thecalclibrary.com/embed/margin-interest-calculator" width="100%" height="640" style="border:1px solid #e2e8f0;border-radius:12px" loading="lazy" title="Margin Interest Calculator"></iframe>The only condition is that the credit line stays visible. It sits inside the frame, so you do not have to do anything to keep it.