Summary
If you make 20,435,904 円 a year living in Japan, you will be taxed 6,547,542 円. That means that your net pay will be 13,888,362 円 per year, or 1,157,363 円 per month. Your average tax rate is 32.0% and your marginal tax rate is 38.4%. 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 38.42 円, hence, your net pay will only increase by 61.58 円.
Bonus Example
A 1,000 円 bonus will generate an extra 616 円 of net incomes. A 5,000 円 bonus will generate an extra 3,079 円 of net incomes.