If you have 30% coinsurance, it means you pay 30% of any expenses eligible for an insurance claim. Meanwhile, the insurer takes care of the rest minus the deductible. For example, you need to pay $7,000 for various bills and have a $1,000 deductible. You’re responsible for 30% of $6,000 — $1,800 — plus your $1,000 deductible. Your insurer covers the other $4,200.