How to filter a report for last two month's of data using prompts?

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Can anyone suggest a way to filter a report using a prompt to capture the last two month's of data?

So ideally we'd add a filter such as "Req First Fully Approved Date Between {prompt} and {2 months prior to prompt}"

This would achieve an auotmatic limit for the report of only two month's data ie. the user wouldn't be able to select, say, six months of data

Look forward to your comments

Ian