Thank you, bro!
I solved it, with your advice C:

Hi mate, thanks for you reply!
But i did it, my algorithm return progress equals 0 when user's rank is 8.
When i test it, everytime i got 0 points progress when users' rank is 8.
So I really don't know what's wrong with my algorithm :C

After applying rank of 8 the progress was expected to be 0, but was actually 1 expected:<0> but was:<1>
What's wrong?
I did that difference with 2 or more ranks worths 1 progress point.
and after getting rank 8, you couldnt up your progress anymore

Did it work with just Expection?