Something I like to do is downgrade pants. I'll go shopping in them, watch TV, write, cook, go for walks, bike. Just when they're on the last legs, I'll subordinate them to garden work, landscaping and car washing. Their final stage in life comes when I paint the house in them. Then they die for good, giving new meaning to the term rigor mortis.
Formal trousers are another matter.
They usually last longer because we wear them less. If styles don't change drastically, and they haven't since the 60s and bellbottoms, they should last 10 years or so. The trick is you can't gain any weight. That is strictly a no-no if you want to maintain your wardrobe. I wore them more this year than in most because it was colder than recent years.