My question is pretty straight forward. I am going to have 20 recepticals and 16 recessed lights to wire. I have plenty of room for additional breakers in my box I also prefer using 20 amp breakers 12/2 wiring. How do you calculate how many lights and recepticals can go on one circuit? My maximum length of run will be approx 90ft.

In the US there are no limits in a residential setting, so this is just my own educated opinion.

I would put ten receptacles on a circuit, and all the lighting on one circuit.
I would also NOT use #12 for the lighting. If you do use the #12 for the lighting you'll see afterwards why I said this.

Stanforty, why would you NOT use #12 other than cost?
I agree with the 3 circuits.
dwdon, you can have 30 65 watt bulbs on a 20 Amp circuit.

I almost never use #12 for residential lighting circuits. I also use #14 for certain receptacle circuits.
It is way too much of a pain to work with, fills switch boxes up MUCH faster (box fill wise), is horrendous when 3-ways and 4-ways and dimmers are involved, and IMO there is NO good reason to use it.
Capacity is also a non-issue IMO. I just a few more circuits in the scope of a whole house. It's not like the load on a circuit is going to change much, especially in a new house.

I don't subscribe to the "bigger is always better" philosophy. I subscribe to the "work smarter, not harder" philosophy.

I Believe "Do it right Once and Forget abot it". Not sure if we can use #14 down here yet, even if we could I would likely only use with lighting circuits. 99.9% of work I do is in conduit, plus 1 or 16 lights only need one set of wires at switch box, and use X rings if they need, I use X ring at most switch locations for future upgrade with Automation devices. I also use stranded #12 , fits in boxes better and less stress on devices.

I forgot you are in #12 and conduit country.
Hey, to each his own, and deal with the requirements in your area.

I certainly DO feel using #14 in a logically wired circuit most definitely IS doing it right the first time.