Window Installation Cost. The average window installation cost is $4,400. This assumes you’re adding or replacing between 5-10 windows. As you may expect, the more windows you add, the higher your cost will be. We have seen single window installations cost as little as $1,200 and 10+ window projects cost as much as $20,000. Assuming you’re not replacing all the windows in your home, expect to pay between $3,100 and $5,100.