Win Rate Tracker on Dashboard

Please find below several SuiteAnswers articles that might resolve your query:

Create an Opportunity Search That Counts Closed Won Opportunities per Customer in a Certain Period

Create Opportunity Saved Search to Display Total Number of Closed Won and Closed Lost in One Column

Create a Saved Search that Shows the Percentage of Opportunities Won vs. All Opportunities in a Given Period

You can then add the results of these saved searches to your dashboard. You may want to convert a Saved search into a KPI display if you follow up the SuiteAnswers below:

Creating a New Search to be used as KPI display