You can only drop COBRA and sign up for a Marketplace plan and premium tax credits during Open Enrollment. You will have to drop your COBRA coverage effective on the date your new Marketplace plan coverage begins. After Open Enrollment ends, however, if you voluntarily drop your COBRA coverage or stop paying premiums, you generally will not be eligible for a special enrollment opportunity and will have to wait until the next Open Enrollment period. The exception to this rule is if your former employer agreed to help pay your COBRA premiums for a period of time, e.g., for the first six months. When employer contributions to COBRA premiums cease, you can also qualify for a special enrollment opportunity to switch to Marketplace coverage.