To develop a tax calculator app like H&R Block, focus on key features such as tax calculation for various income types, deduction and credit management, secure data storage, and a user-friendly interface. Additional features like e-filing, document upload, real-time tax law updates, and AI-driven personalized tax advice can enhance the app's value. The development cost typically ranges from $15,000 to $50,000, depending on the app's complexity, platform choice (iOS/Android), and the development team's expertise. It’s crucial to ensure compliance with tax regulations and data privacy laws. For expert development services, consider DevTechnosys for reliable solutions.