Health Insurance begins on the effective date that is chosen. Choosing an effective date can vary by insurance company. Some  Medical Insurance  companies offer an effective date of the next day from applying for coverage. If you have not had previous Medical Insurance prior to applying for coverage, a short waiting period may be imposed and you should apply for health insurance immediately. A health insurance policy must be underwritten, once it is approved, the  Medical Insurance coverage is retroactive back to the chosen effective date.