To create a watchlist column with YTD values use the ROC() function set to Yearly timeframe (so the change will be calculated from the close of the last yearly bar). Note: if you want to display as a percentage in a watchlist column divide the result by 100:
If you have divided by 100, right-click on the watchlist column header and change the Column Type to Percentage. It’s also possible to colour code the cells under Custom Labels, eg green > 0 and red < 0 values (note: delete the Label text so just the value shows, as per the example).
You can also show summary information for the column, such as the count (number of items in the list), Average, or Sum. In the Watchlist properties enable Show Summary Row, and to show the average YTD% right-click in the grey bar of the YTD column and under Summary Type select Average: