The design life of a component or product is the period of time during which the item is expected by its designers to work within its specified parameters; in other words, the life expectancy of the item. Engineers follow a theory to calculate the life expectancy from expected conditions, uses and physical properties. It is not always the actual length of time between placement into service of a single item and that item's onset of wearout.
Another use of the term design life deals with consumer products. Many products employ design life as one factor of their differentiation from competing products and components. A disposable camera is designed to withstand a short life, whilst an expensive single-lens reflex camera may be expected to have a design life measured in years or decades.
