If you make 1,200,000 円 a year living in Japan, you will be taxed 232,620 円. That means that your net pay will be 967,380 円 per year, or 80,615 円 per month. Your average tax rate is 19.4% and your marginal tax rate is 19.4%. This marginal tax rate means that your immediate additional income will be taxed at this rate. For instance, an increase of 100 円 in your salary will be taxed 19.39 円, hence, your net pay will only increase by 80.61 円.
A 1,000 円 bonus will generate an extra 806 円 of net incomes. A 5,000 円 bonus will generate an extra 4,031 円 of net incomes.
NOTE* Withholding is calculated based on the tables of Japan, income tax. For simplification purposes some variables (such as marital status and others) have been assumed. This document does not represent legal authority and shall be used for approximation purposes only.