Monthly Return is the period returns re-scaled to a period of 1 month. This allows investors to compare returns of different assets that they have owned for different lengths of time.
How YCharts Calculates Monthly Returns:
Monthly Return = Closing Price on Last Day of Month / Closing Price on Last Day of Previous Month
People frequently convert annual returns to average monthly returns using this formula:
Monthly Return = (Period Ending Price/Period Beginning Price)^(1/12) – 1