"Daily Margin Interest (Short Position) = The Daily Market Value of the Borrowed Stocks when Market Closes* Margin Rate for That Stock/360." http://www.webull.com/pricing
I thought it was an accounting convention. They use 360 days as the standard value for a year. But what do I know. I hated accounting in college. Lol.
"MONTHLY?" My favorite is the number of weeks in a month: "Well! Just multiply by 4!" No. There are 4.3333 weeks in the average month, so a weekly paycheck gets reduced when figuring monthly income; weekly-paid costs get reduced when figuring month totals...