Let's say that I have a margin account at a major broker like TD Ameritrade or Interactive Brokers. I am trying to calculate what my cost would be to use margin and I would also like to know when it would be charged.

For simplicity's sake, let's say that the margin stays fixed for 1 year and the borrow rate is 5%. Can I say then that my total cost on $10,000 margin would be $500 a year for a monthly rate of $42?

Do brokers like these charge interest on a daily basis?

1 Answer 1


If the amount borrowed remains constant at $10,000 and with a 5% borrow rate then your calculation is correct.

At IBKR, the margin interest accrues daily and it is deducted from your account at the beginning of the each month. Though I have an account at Ameritrade, I haven't used margin there. I'd assume that the process is the same. A quick call to them would provide the answer

  • So would that mean that I would be charged roughly a 1.36 a day? May 29, 2019 at 18:18
  • @laptop2d Yes, that would be the correct math. $1.36 per day on a $10k margin. IB charges your account monthly.
    – Brian R
    May 29, 2019 at 19:45

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