The average lifespan of a countertop microwave oven is typically around 5 to 10 years, depending on usage and maintenance. With proper care and regular cleaning, you can extend the lifespan of your microwave oven.nnIt's important to note that certain factors such as power surges or mechanical issues can affect the lifespan of your oven. Regularly checking and servicing your microwave can help ensure its optimal performance and longevity.