Summary
If you make 8,238,432 円 a year living in Japan, you will be taxed 2,160,637 円. That means that your net pay will be 6,077,795 円 per year, or 506,483 円 per month. Your average tax rate is 26.2% and your marginal tax rate is 25.7%. 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 25.73 円, hence, your net pay will only increase by 74.27 円.
Bonus Example
A 1,000 円 bonus will generate an extra 743 円 of net incomes. A 5,000 円 bonus will generate an extra 3,714 円 of net incomes.