There is no set answer. When you will need to repaint mainly depends upon the quality of the materials used, as well as the condition of the substrates (whatever is being painted), exposure to the elements and the colors (some colors are less stable than others). Depending upon the product used, clear wood sealers can last for as little as 6 months and up to 2 years, semi-transparent stains may last 3-5 years, solid stains 4-7 years and properly applied paint finishes 5-15 years. The preparation, priming and number of finish coats, as well as the quality of the paint, are all determining features.