Although it’s fun to have a web site guess at your student’s percentage chance at each college, I think it’s probably misleading, whether it’s conservative or optimistic.
But you don’t need percentages. The main purpose of “chancing” is to build a practical list. You need at least one or two likely schools. You don’t want to drive yourself crazy applying to a whole lot of unlikely high reaches. And it’s nice to have a bit of variety in the target and reach category, since admission in these categories is less predictable.
I like the College Kickstart method. CK is a pay service, but you can use their method yourself. (The below screenshot is just my google sheets sketch of their categorization system.)
For each institution, the row is determined by the school’s selectivity (admit rate). Be as precise as possible (for example if you know admit rate for the student’s major, use that one).
The column is determined by comparing the student’s stats to each institution’s publicly posted ranges for GPA and test scores. Again, be as precise as possible.
It’s a bit subjective when the GPA and test scores appear in different ranges for that institution. In that case I try to be more conservative.