Basic health insurance:
For mandatory basic insurance the following applies: your application to a new company is provisional until they receive confirmation of your cancellation from your current insurer. This way, no one has to pay double premiums for basic health insurance if they missed the cancellation deadline.
Applications for supplementary insurance are legally binding, which means that, after submitting the signed offer, the applicant is bound for 14 days (Insurance Policies Act, Art. 1). Should he be denied supplementary insurance, or only be accepted with certain restrictions, the applicant is freed. However, if a medical examination is required, the applicant will remain bound for 4 weeks. There is no right of withdrawal as is the case for door-to-door sales, unless the contract explicitly states the right of withdrawal.
Double insurance is possible with supplementary insurance: If an application is accepted but the applicant missed the cancellation deadline for his former insurance company, he has to pay both premiums. The new insurance company may agree to postpone or suspend coverage, but is not obliged to do so.