The cr of the animal + what awakened adds (is it +1?). It then has to earn any class levels. It should loose any benefits if it was an animal companion. Awakened animals can be followers just fine.
In my game, the DM decided that an awakened heavy horse would start at cohort level 5. A heavy horse is CR 2 with two hit dice, but he felt it was more on par altogether with CL 3. Then, the Awaken spell added two levels, so it came out to CL 5. From there, I leveled him up as a Fighter. He also allowed it to have d10 had instead of d8. It's worked very fairly.
Beyond that, I'm not aware of any rubric that neatly translates it for you. If you search the forums for discussions on CR and CL, you'll see what I mean.
Why does that suck? The cohort can learn class levels after. Mr. Cave bear can become a tetori monk if he wants.
Its just neither awakened or being a cohort grants levels by raw.
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You can also check out the article "Beast Leaders" in Kobold Quarterly 18.
It covers this exact topic (as well as other, closely related topics)!