Achieved % is the amount that has so far been accumulated for the goal. As you start allocating assets to a goal, this amount gets updated with the current value of the asset. As and when the client makes further investment this amount will be updated dynamically. 


Additionally, for the assets that are linked to this goal, on a daily basis their values keep updating themselves. E.g. Mutual Fund NAV, stock prices, values of fixed deposit or recurring deposit etc. to name a few. This will keep updating the achieved % whenever you/client loads the goal tracker section.