In Tamriel Unlimited (Elder Scrolls Online (ESO)) there is a Champion Point system and by adding champion points to the Mage constellations (Apprentice, Atronach and Ritual constellations) characters can gain additional Magicka. Below is a calculator which will calculate the effects on Magicka with changes in points in the tree. The data used to derive the equations was gathered by @Bouvin. It should be noted that while 400 points (100 per star) may be put into each constellation (meaning 1200 are possible for the Mage), only the first 1000 points will increase you Magicka. This was discovered by @Soulac and many thanks to him for this tidbit. He created and supports standalone build planner that fulfills a slightly different purpose than my calculators.
If you encounter a wildly inaccurate calculation please submit it through the Contact Us Forum on the homepage.