Can you enroll in ObamaCare whenever you want?
You can only enroll in health insurance under the Affordable Care Act (ObamaCare) during Open Enrollment (Nov 1 - Dec 15 each year) unless you qualify for Special Enrollment.
For example, if you move or lose your plan for any reason other than non-payment, you may qualify for a short special enrollment period where you can enroll in a new marketplace plan.
This rule applies to all individual and family coverage obtained privately, such as plan purchased on the Health Insurance Marketplace HealthCare.Gov.
With that said, you may qualify for insurance not sold on the marketplace at other times of the year.
For example, Medicaid / CHIP is offered all year round, and Medicare and employer coverage have unique enrollment periods and rules.
Learn more about Open Enrollment.
Learn more about Special Enrollment.