I've read the margin documentations on IB but am not sure given the following scenarios. I have a reg-t margin account trading stocks/etfs.

Scenario 1:

I do weekly re-balancing of a portfolio of 1-10 securities. I am to be invested at all times but my portfolio will change each week. When I start trading, everything will be ok as I have all cash. But when re-balancing comes along, I must sell all my security holdings and invest in new ones the following week. Since its t+3, I wont get cash settlement until the third day after I've sold my holdings. But given my need to re-balance on the same day I sell all my securities, I will need to use margin to purchase new holdings, is this correct? If so, after 3 days, when my cash does come back in, what happens? Is it still a position on margin?

Scenario 2:

I have a concentrated position on that takes the entire value of my portfolio. No cash left, just 1 big position. (risky, i know) In such scenario, since the position is financed by my cash, no margin comes in to play, correct? What happens when I decide to increase my position using margin? Under the Reg-T margin rules, any position that is traded on margin requires the trader to pay 50% of the value, but I don't have anymore cash, will the new trade be denied?

Thanks so much, anything will help.

2 Answers 2


Scenario 1 -

When you sell the shares in a margin account, you will see your buying power go up, but your "amount available to withdraw" stays the same until settlement. Yes, you can reallocate the same day, no need to wait until settlement. There is no margin interest for this scenario.

Scenario 2 -

If that stock is marginable to 50%, and all you have is $10,000 in that stock, you can buy another $10,000. Once done, you are at 50% margin, exactly.


You have to call Interactive Brokers for this. This is what you should do, they might even have a web chat. These are very broker specific idiosyncrasies, because although margin rules are standardized to an extent, when they start charging you for interest and giving you margin until settlement may not be standardized.

I mean, I can call them and tell you what they said for the 100 rep.


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