Income Tax Article 21 (PPh 21) is a tax on income in the form of salaries, wages, honorarium, allowances and other payments. Taxes are received by domestic individuals in any form related to the work or position, services and activities carried out by that person. Tax calculations are still done manually, which is a problem that often arises. To overcome this problem, the PPH 21 application is designed to assist employees and companies in calculating and paying PPH 21. The main features of this application include calculating PPH 21 and generating PPH 21 reports automatically, making it easier for users to provide PPH 21 to be paid by employees. This study uses the extreme programming method in developing the system. The results of the test show the success of the system for each input and the accuracy of PPH 21 calculations under different conditions. In non-functional testing it shows success when the system is used on several different devices with the results of the system adjusting the screen size according to the device used (responsive).