My baby birth weight was 3.820 kg now he is 4.200 kg at 26 days of birth is this good

A. It’s an average weight gain I must tell you that the child should gain at least 500 g in a month your child is a little less as per the expected weight gain so maybe hopefully by next time your child is going to get about 600 g in a month and if that does not happen then you can consult the doctor and can start giving formula