Let's create a Summary report:
- Use the Opportunity report type.
- Group by Stage and Close Date (Group Dates by Calendar Month).
- Add the summary formula and name it Prev Month Won with this formula: PREVGROUPVAL(AMOUNT:SUM, CLOSE_DATE).
- In this exercise, I'll filter the report to show the only Opportunity for 2 months of Close Date; This is only for simplicity in order to reduce data in the report, see the following screenshot for details:
- Add the formula summary to the Summary report.
- Add the Amount field and summarize it with Sum. You would see something similar to this report: