This is an excellent question and one we hear a lot. I know you asked about assistance for day-to-day care. But the side-question I would ask, what type of "professional help" do you need? There are a multitude of professional services: medical, psychological, care-giving..... I would suggest you first ensure that you have the right diagnoses for your parents. This will inform what type of cognitive issues you are dealing with and what type of care you may dealing with now and in the future. You may also need help defining that type of care and the safety issues surrounding cognitive decline. Back to your original question - when to bring in care-givers. Many people wait until a crisis hits and that is too late. You need to gauge the ability of your parents' current support system, understand the gaps (or where someone is doing too much and approaching burnout). Then fill those gaps with a professional care-giving agency. Your mother may accept a small amount of help now, especially if you let her know it is for your peace of mind. This care can often grow as she begins to see the benefits.