I am interested in Electrical Work. I have been doing electrical work for some time. My question is... If I have a 100amp or 200amp service pannel and I want to install a lighting circuit how do I caculate the amount I can use. I am using 14 gauge romex wire and I am coming off a 15 amp breaker.

Your lighting load can't be more than 80% of 15 Amps because the load can potentially be on more than 3 hours at a time and thus qualifies as a continuous load and therefore must be derated.

Whether you can add another 15 amp circuit or not depends on the other connected loads and what may be running at any one time. I am asking to have thing moved to electrical and lighting. To get a reliable answer, you will have to give the size of the house and major appliances, A/C, hot water, etc.

Sounds like you want to know if an existing service has the capacity to add more load.

If you have been doing electrical for some time, I am sure you have a copy of the National Electric Code.

If not,

In the Read This First sticky note at the top of the Electrical forum:
https://www.askmehelpdesk.com/electrical-lighting/read-first-all-electrical-questions-48863.html

Find the link and instructions to the National Electric Code:
NFPA 70: National Electrical Code® (http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=70&cookie%5Ftest=1)

And review Section 220.83, and get back with any questions you have