The Health Check score is calculated by a formula to measure how well your existing security settings meet the Salesforce Baseline Standard or your selected custom baseline.
There are four risk categories in the Health Check: High-Risk, Medium-Risk, Low-Risk, and Informational. These risk categories tend to affect the score of your Health Check, with High-Risk settings counting the most, Low-Risk settings counting the least. Settings that remain in the Informational category do not factor into your Health Check score.