We are researching and developing the toilet timing suggestion method for the elderly in order to support their comfortable outing because the elderly are likely to experience frequent urination and often encounter the difficult situation of searching for a restroom with holding their water. Our proposed system calculates the toilet timing in consideration with both their outing schedule and the amount of body water of them, and recommends going to a restroom sufficiently before they feel the need of urinating. In order to implement the system, we've come up with the physiological formula for non-invasive estimation of the amount of body water, and based on the estimation, the toilet timing is calculated. Also, we've devised the suggestion method of the toilet timing to the elderly in order both not to interfere their things to do while their outing and not to be ignored by them. In this paper, we describe our proposed system, and show the experimental result for evaluating both the toilet timing calculation and the suggestion method. © 2012 IEEE.