I've come to Japan with the intention of working for two years. However, for those staying more than one year, income tax is withheld in the same way as for Japanese citizens, deducted from the monthly salary and calculated for the year. Adjustment usually takes place at the end of the tax year, and returns or collections are made accordingly.
Income tax is calculated based on the income.
The main purpose of National Health Insurance is to reduce personal liability for medical treatment. Fixed premiums are paid monthly and are calculated according to such factors as income and size of family. If you leave Japan before the end of the year or become disqualified from the system, returns will be made following calculation of the monthly installments. Foreigners who stay in Japan for more than a year should register for National Health Insurance. There is also another health insurance system for laborers.