What is the purpose of a 'deductible' in a health insurance plan?

A deductible is the amount an insured must pay out of pocket for covered health services within a plan period before the insurer starts paying its share. For example, with a $1,000 deductible, the insured pays the first $1,000 of covered costs before coverage kicks in (some services may be covered before the deductible, such as certain preventive care). The premium, by contrast, is the ongoing amount paid to keep the policy in force. Deductibles are part of cost-sharing along with copayments and coinsurance. Understanding the deductible as the insured's upfront cost-share before benefits begin is fundamental health insurance content.