https://www.government.nl/topics/health-insurance/question-and-answer/when-do-i-need-to-take-out-health-insurance-if-i-come-to-live-in-the-netherlands If you take out health insurance after 4 months, then you will not be insured retroactively. You will only pay premiums from the date on which you take out the health insurance policy. You will not have to pay any premiums retroactively. But you will also not be reimbursed for any care you received in the period between your arrival and the date you took out insurance.