GST Calculator - Tool is a free Android application developed by Zoomtook that is designed to help users calculate Goods and Service Tax (GST) on sales or purchases of goods or services. The app is a combination of two calculators, the Simple GST Calculator and the Combined GST Calculator, both of which are useful for quick and accurate calculations.

The Simple GST Calculator has a user-friendly interface that allows users to enter the initial amount of a transaction and the GST rate and get the results calculated as they type in. It also shows the amount inclusive or exclusive of tax amount and allows users to add or remove the GST from the given amount with the touch of a button. Additionally, the app offers custom tax rates and pre-provided rates of 3%, 5%, 12%, 18%, and 28%.

The Combined GST Calculator is equipped with a GST Calculation Box that allows users to copy and share the GST calculations and shows the bifurcation of the taxes as per the current Indian Goods and Service Tax system in the form of IGST, CGST, and SGST. It also includes basic mathematical calculations such as addition, subtraction, multiplication, division, and percentage-based calculations. The app has a scrollable calculation view to keep track of what users are calculating.