If you make 1,200,000 KSh a year living in Kenya, you will be taxed 309,383 KSh. That means that your net pay will be 890,617 KSh per year, or 74,218 KSh per month. Your average tax rate is 25.8% and your marginal tax rate is 31.4%. This marginal tax rate means that your immediate additional income will be taxed at this rate. For instance, an increase of 100 KSh in your salary will be taxed 31.38 KSh, hence, your net pay will only increase by 68.62 KSh.
A 1,000 KSh bonus will generate an extra 686 KSh of net incomes. A 5,000 KSh bonus will generate an extra 3,431 KSh of net incomes.