Summary
If you make 8,245,128 円 a year living in Japan, you will be taxed 2,162,360 円. That means that your net pay will be 6,082,768 円 per year, or 506,897 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 25.74 円, hence, your net pay will only increase by 74.26 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 3,713 円 of net incomes.