No fake leaderboard here. I have not tested every app, and a definitive ranking without methodology is a sales pitch. Compare any calculator on these seven things instead. - Data source: does it show the year each rate took effect? A calculator lives or dies on its table. - Coverage: thirty countries or two hundred? - Rate types: headline only, or small-business and effective rates too? - Update cadence: a 2023 app is a paperweight with a nice icon. - Offline access: you will want this in a meeting with bad wifi. - iOS and Android parity: your co-founder has the other phone. - Export and sharing: a number you cannot send your accountant is trivia. The app does the arithmetic; the database tells you whether the arithmetic is current. IncorpTrack's free 212-country table is the thing worth comparing against, and the UK/Singapore registration service runs $49 plus the government fee.