If you make K 1,800,000 a year living in Zambia, you will be taxed K 688,855. That means that your net pay will be K 1,111,145 per year, or K 92,595 per month. Your average tax rate is 38.3% and your marginal tax rate is 38.5%. This marginal tax rate means that your immediate additional income will be taxed at this rate. For instance, an increase of K 100 in your salary will be taxed K 38.50, hence, your net pay will only increase by K 61.50.
A K 1,000 bonus will generate an extra K 615 of net incomes. A K 5,000 bonus will generate an extra K 3,075 of net incomes.