You can change your health insurance company only once a year and only on 1 January. There is one exception: you can change your health insurance company during the year if you switch from one collective employer’s agreement to another (i.e. if you switch jobs).
You have to cancel your health insurance before 31 December. Your new health insurance company may offer to cancel your old insurance on your behalf. If they don’t offer this, it is best to send an aangetekende brief (registered letter) well in advance. A health insurance company is obliged to accept you for basic insurance, unless there are some payments overdue/outstanding at the current health insurance company. In such a case, the new company can refuse you basic health insurance.
The new health insurance company is allowed to refuse you for additional health insurance if you don’t meet its requirements. Therefore, it is advisable not to cancel your current additional health insurance until you have received an email or letter that the new company accepts you for additional insurance.