How this instrument works
A margin loan balance is money a brokerage lends against securities already sitting in the account, so a trader can hold more stock, bonds, or funds than cash on hand would allow. The broker charges interest on that borrowed balance every single day it stays outstanding, whether the position bought with it is up or down — the loan does not track the trade's result, only how much is owed and for how long.
The formula divides the quoted annual rate by 100 and by 365 to get a per-day charge, then multiplies that by the balance and by the number of days held. That day-count convention is what most margin agreements print in the fine print, rather than a flat monthly bill like a mortgage payment. Hold the same balance for exactly 365 days and the daily accrual collapses back to the stated annual rate — a quick way to check the arithmetic.
Real broker rate schedules are tiered rather than flat: the debit balance is sliced into bands, and the rate usually drops as the balance climbs into six or seven figures, and most brokers reprice the whole schedule whenever a reference rate such as SOFR moves. This instrument holds one flat rate across the entered period, so it prices a fixed-rate quote correctly but will drift from a real bill if a balance crosses a tier or a rate changes mid-cycle. It also has nothing to do with a margin call, which is triggered by account equity falling below a maintenance requirement, not by the interest charge itself.
- Enter the amount borrowed in Margin loan balance, $ — the debit balance a brokerage statement shows, not the value of the securities held.
- Set Broker's margin interest rate, % to the annual rate quoted for your account's balance tier.
- Enter Days the balance was held for the stretch you want interest on — an overnight hold and a multi-month position both work.
- Read Interest charged for the dollar cost of carrying that balance over exactly that many days.
Worked example — $10,000 held 30 days at 8%
Take a $10,000 margin loan balance charged at 8% annual interest, held for 30 days. The daily rate is 8 ÷ 100 ÷ 365 = 0.0219178%, and multiplying that by $10,000 gives $2.19178082 per day. Thirty days of that daily charge comes to $65.7534246575, which the sheet rounds to $65.75 — the exact figure a brokerage would post if the balance never moved for the month.
That $65.75 is the price of carrying the borrowed half of a trade, owed regardless of what the shares bought with it do next — a position financed this way needs to clear roughly an 8% annualized return just to offset the loan, before commissions or the trader's own cash at risk are counted. Double the balance to $20,000 at the same rate and days and the charge doubles too, to $131.51, because the formula is linear in balance.
Questions
Why does margin interest accrue daily instead of monthly?
Because a margin debit balance can change any day trades settle, funds move, or buying power gets used, daily accrual lets a broker charge for exactly the days each dollar was actually borrowed. Dividing the annual rate by 12 would treat every month as identical length; the days-in-year convention used here reflects the real calendar instead of a rounded monthly average.
Do I owe margin interest even if my position is losing money?
Yes. Margin interest is the cost of the borrowed money itself, charged on the outstanding balance regardless of what the securities bought with it are currently worth. A losing position still accrues the daily charge — it shrinks only because the balance is paid down or fewer days are held, never because the trade turned unfavorable.
Why doesn't this match the interest line on my brokerage statement?
Most brokers post a tiered rate schedule where the rate drops as the debit balance grows into higher bands, and they typically reprice the whole schedule when a reference rate such as SOFR moves. This instrument applies one flat rate across the whole period entered, so a balance that crossed a tier or a rate that changed mid-cycle will price slightly differently on the real statement.
Is margin interest the same thing as a margin call?
No — they are separate mechanisms. Margin interest is simply the daily cost of the borrowed balance, which is what this sheet calculates. A margin call happens when account equity falls below the broker's maintenance requirement and has nothing to do with the interest rate itself; a balance can accrue interest normally for months without ever approaching a call.
What return does a leveraged position need just to break even?
At minimum, enough to cover the margin interest rate itself, since that cost accrues no matter how the trade performs. On the default sheet, an 8% annual rate means the borrowed portion of a position needs roughly an 8% annualized gain before commissions just to offset the interest — anything below that and the leverage is adding a cost the return isn't covering.
Does the days-held figure include weekends and holidays?
Yes — margin interest accrues on every calendar day the balance stays outstanding, weekends and market holidays included, because the loan does not pause when trading is closed. A position carried over a three-day weekend accrues three days of interest even though only one trading session falls inside it.
References
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.