In my opinion, the best place to check Initial/maintenance margins is the CME’s website. For example, here is the margin page for the E-mini S&P 500: https://www.cmegroup.com/markets/equities/sp/e-mini-sandp500.margins.html
The CME does not list the initial margin, however. Initial margin is 10% more maintenance margin. You can calculate this by taking 1.1 x maintenance margin. For example, at the time of writing this post the ES maintenance margin is $10,800.
10800 x 1.1 = 11,880
Meaning the initial margin of this product is $11,800. A trader must have $11,800 per position of the ES at the time of this response in order to hold these positions into the market close.
For intraday margins, we simply take a percentage of the exchange initial margin requirement. Day trading margins can vary from trader to trader based on risk managementa and due to the fact that we work with different FCMs, each FCM offering different margins.
To find out what your day trading margins are for your account, we suggest you email us directly at: firstname.lastname@example.org.
We hope this helps!