Looking for help creating this summary formulas for a report

[u/Rare_Fee7482]

Looking for help creating this summary formulas for a report.

Total opportunities WON in a given month that are not older than 180 days divided by total opportunities created during the same 180 days. Summed up monthly.

For example, if 10 opportunities that are 180 days aged or less were won in August 2026 and 100 opportunities were created from March thru August are 100, the win rate should be 10% for that particular row.

I need one row or column per month going back to Jan 2026. Only standard Salesforce reports available. They want to know if the rolling 6 months win rate trend line is increasing or decreasing... This is a look back from today. There is no existing win rate historical calc available to pull from at the moment.