How do I delete files from a folder by month using Powershell or CMD?

When you say by month I am assuming your referring to the modified date.
This one will delete all .txt files older than 30 days.
CMD

forfiles /p "C:\temp" /s /m *.txt /D -30 /C "cmd /c del @path"

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Powershell (all items older than 30 days)

Get-ChildItem –Path "C:\temp" -Recurse | Where-Object {($_.LastWriteTime -lt (Get-Date).AddDays(-30))} | Remove-Item

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Thanks Robert! yes, i meant File modified date.

But I would like to delete only the files that were modified in Jan 2011. And then later I would like to delete files for Feb 2011. I can run the command again as needed. Can you please suggest how that can be done?

Thank you!