AbstractAssume a component has a constant failure rate during the first τ unit of time following installation. After that, wearout sets in so that failure rate begins to increase sharply. Assume further that replacement is made at the time of component failure or at τ units of time following installation, whichever occurs first. Under these assumptions, we obtain explicit formulas for the distribution and expected value of the number of planned replacements, the number of failures, and the total number of removals due to either planned replacement or failure replacement, corresponding to any specified length of time. Examples are worked to show the application of these formulas. The results obtained in this article are of use in determining the number of spares to stock or the budget required to maintain the equipment.