The amount that is "too much" to cut off a tree depends on various factors, including the tree's species, age, health, and size. In general, you should avoid removing more than 25-30% of a tree's canopy in a single pruning session, as this can stress the tree and lead to potential health problems. However, it's best to consult with a certified arborist or tree care professional for specific guidance based on your tree's unique characteristics and needs.