The American Joint Commission on Cancer or AJCC has a staging system for all cancers including melanoma. Using melanoma thickness, the presence or absence of lymph node metastasis and presence or absence of systemic (body) spread, the staging system will place you in a Stage that corresponds to a percentage of patients who survival for a specified time period (typically 5 years). This staging system is updated every few years to insure it has the latest data on melanoma. This is only for patients who have had a melanoma. As far as calculating your risk of getting a melanoma, there is no model where you plug in parameters and then get your chance of getting melanoma.