Hopefully this info is helpful to some. I took the numbers for calculating levels and crunched them out for the following:
To begin with, each time you improve a skill, you gain that skill's value in experience. So if you go from 30 to 31 in archery, for example, you gain 31 'experience points'. To gain a level from a previous level, you need your (current level + 3) * 25 xp. So to go from level 1 to level 2, it requires 100 experience points (1+3)*25. To go from 17 to 18 it requires 500 experience points (17+3)*25. All this is well and good, but what does this mean?
I've seen some posts about character builds and what is required for them. Most of these builds specialize in particular skills, often taking them to 100, sometimes in the absence of all other skills. The purpose of this post is just to demonstrate some of the limits that are imposed when you are planning such a character.
To take a skill from 25 to 100 (a race's 1 'best' skill) will give you 4725 experience points. To take a skill from 20 to 100 (a race's 5 'minor' skills) will give you 4840 experience points. To take a skill from 15 to 100 (a race's 12 'untrained' skills) will give you 4930 experience points.
What this means is if you specialize strictly in 6 untrained skills (e.g., an imperial taking all thief skills to 100), you will only gain 29580 points. This is enough to take you level 46, with 45 perks.
The cutoffs for levels 30-80 in ten level increments are as follows: