Indonesia has developed the National Health Insurance System (NHIS), aiming to achieve the Universal Health Coverage. However, there was deficit problem during 2014 to 2019. The trend is likely to increase. This study aims to evaluate and plan further policies with efficient premiums amount. System dynamic is applied to simulate the effects of ability-to pay, willingness-to-pay, salary, age, health cost each customer, and fund inventory. The results show that the health costs considered for determining the premiums are critical to the financial stability of the NHIS.