Baby sleeps 12+ hours a day??

Is it normal for my 4 month old to only stay awake for about 9 hours a day? She doesn't really have a sleep schedule cause I'm a stay at home mom so she just sleeps when she wants. I also co sleep so at night when she gets hungry I just feed her and she goes right back to sleep, so she stays asleep longer. I just didn't know if this is healthy or normal.. Any advise?