This site has been providing a free on-line maximum demand calculator since 2010. This year, for its third birthday, I gave it a revamp, so it looks better and works better on modern phones, tablets and computers.
I’ve just added a discussion forum, so you can ask any questions that have been burning on your mind about the wiring rules, or help out a mate by answering a question. There’s also a place to discuss anything else relating to electrical work.
I hope you find it useful and easy to use!