It's not per day. Yo have to read the post right below OP. It's all explained there.
4% per day is never legit. That would be 120% a month. Only ponzi schemes can offer that much. If it was legit nobody would be trading anymore as most traders barely make 10% a month. People who could earn 120% without lifting a finger would just put 0.1 bitcoin there and quit their day jobs.
OP obviously misunderstood the plan, I would mark the site HYIP or Ponzi scheme if it is 4% daily because it's not sustainable not even a big company or a bank can give you 4% daily interest but 4% annually with compounding is just right and sustainable I have never seen a site that can sustain even 3% daily interest I remember seeing a lot of program offering 3% and they are all reported and within a month the program was offline.