What are work credits for determining SSDI eligibility?

What are work credits for determining SSDI eligibility?

• Work credits are based on your total yearly wages or self-employment income. You can earn up to 4 credits each year. The amount needed for a credit changes from year to year.
• The number of work credits you need to qualify for disability benefits depends on your age when you became disabled. Generally, you need 40 credits, 20 of which were earned in the last ten years ending with the year you become disabled.
• Younger workers may qualify with few credits