The formula
needed average = (target × (credits done + credits left) − current GPA × credits done) ÷ credits left
Say you have a 3.0 after 60 credits and want a 3.3 by graduation, with 60 credits left. You need (3.3 × 120 − 3.0 × 60) ÷ 60 = 3.6, roughly A− work in every remaining course.
Why it gets harder over time
Every credit you have already earned pulls toward your current GPA. After 30 credits, one strong semester can move your GPA by 0.3. After 90 credits, the same semester moves it by less than 0.1. If the planner says a target is out of reach, it also tells you how many credits of straight A's it would take.
Questions
Can I raise my GPA from 2.5 to 3.0?
Yes, if enough credits are left. With 60 credits done and 60 to go you need a 3.5 average. With 90 done and 30 to go you would need 4.5, which is impossible on a 4.0 scale.
Do retakes help more than new courses?
At schools that replace the old grade, yes: the failed credits leave the average. Check your school’s retake policy. The calculator can use replacement or averaging.