public function previousMonth( $date ) {
			if ( PHP_INT_SIZE <= 4 ) {
				if ( date( 'Y-m-d', strtotime( $date ) ) < '1902-02-01' ) {
					throw new OverflowException( esc_html__( 'Date out of range.', 'the-events-calendar' ) );
				}
			}

			// Create a new date object: a badly formed date can trigger an exception - in such
			// a scenario try again and default to the current time instead
			try {
			$date = new DateTime( $date );
			}
			catch ( Exception $e ) {
				$date = new DateTime;
			}

			// set date object to be the first of the month -- all months have this day!
			$date->setDate( $date->format( 'Y' ), $date->format( 'm' ), 1 );

			// subtract a month
			$date->modify( '-1 month' );

			// return the year-month
			return $date->format( 'Y-m' );
		}