Hello Yes there is a difference 잘했어요 is 'you did well' and it is in a polite form as it has "요" attached at the end The same meaning would be 잘했어 which is though in informal form and would be used only to peoplle younger than you or veery close to you 잘한다 is informal form and it is in a present form which means that you would say it if the person is 'doing well' at the moment For example, you are playing tennis and your friend is really good at it you can say '잘한다' (never say it to a person older than you or someone you need to respect!) If you wish to put this into past thense its simply '잘했다' meaning 'you did well' So i think in your situation it is correct to say '오늘 수고했어요. 잘 했어요' Hope this helps^^