i have a 1/2 inch conduit that runs from my panel to the far side of my house and supplies 2 rooms, a hallway and a garage.
currently this pipe contains three 15 amp circuits and a 20 amp circuit. these are multiwire circuits. there are 4 14 gague wires and 2 12 gauge wires.

could i add an additonal 2 amp circuit? to do this i would need to pull an additonal 12 gauge wire and a 14 gague neutral.

then i would have 4 15 amp circuits and 2 20 amp circuits.

simply put, the pipe would contain 6-14 AWG (4 current carrying) and 3 12 AWG (2 current carrying) would this be ok, or would the pipe be over stuffed?

It appears that the answer is you can not, but I just did a rough calculation.

What is the wire type? If it is THHN there is not a problem with the conduit fill or with the ampacity adjustment for more than 3 current carrying conductors.
Don

The wire is THHN

Why would you pull a 14 ga. neutral with a 20 ga. hot?

because the there is a multiwire system in the pipe that has a 20 amp and 15 amp circuit. when i add the second 20 amp, i plan to use the 12 gauge neutral that is already in the box, and pull a new neutral for the old 15 amp ciruit that is currently sharing the old 20 amp circuit's neutral.

basically i would end up with a total of 5 circuits. there would be 3 15 amp circuits. 2 of them would share a neutral and one would have it's own neutral (the 14 gauge that i am pulling). The new hot 12 gauge would be hooked up to the old 12 gague neutral. of course i would make sure all of the breakers for the multiwire circuits are on opposite 120V legs.