What is margin interest?
Margin interest is the cost charged by a brokerage for borrowing money against securities in an account (a margin loan), typically used to buy additional securities.
The formula
Margin Interest = Loan Amount × Annual Rate × (Days Held / 365). Margin rates are usually variable and tiered based on the size of the loan, and interest often accrues daily and compounds.
This calculator is for general education; margin trading involves significant risk, including the potential for losses beyond your initial investment.
Last reviewed August 2026