iOS/Android/Desktop: Default calculator apps suck. They work like a traditional handheld calculator, which only displays one value at a time and can only do basic maths. If you want to do anything more than calculate a sales discount, you’re better off with these free and cheap calculator apps.
These apps help you do typical “real life maths” or solve basic textbook maths problems.
MyScript Calculator 2 ($4.49 on iOS/Android): Write equations onto your phone or tablet with your finger, and MyScript will recognise and solve them. The app supports advanced arithmetic, absolutes and factorials, trigonometry, logarithms, and constants like pi.
Calc+ (free on Android): Type and edit arithmetical calculations to solve. Save calculations or export to notes apps.
PhotoMath (Free and ad-free on iOS/Android): Type or photograph a maths problem (printed or hand-written) to solve and to see a step-by-step guide to the solution. Supports arithmetic, algebra, trigonometry, calculus, and graphing. Great for helping your kid with maths homework, checking your answers, and tackling complicated problems.
AutoMath (free on Android): Similar to PhotoMath, but contains ads and doesn’t support hand-written equations. Type or photograph a maths problem to solve and see the steps to the solution. Supports arithmetic, algebra, inequalities, basic trigonometry, and graphing.
Wolfram Alpha ($4.49 on iOS/Android/Windows Phone, free on web): Enter a maths problem or word problem to solve and get step-by-step solutions. Supports arithmetic, algebra, calculus, trigonometry, geometry, graphing, differential equations, alternate bases (e.g. binary), factorisation, functions, logic, set theory, statistics, probability, definitions and history of maths terms, and real-world variables.
Wolfram Alpha is like a nerdier Google, so it’s great for figuring out complicated real-world maths problems as well as working on advanced maths homework. $9.99 per month pro subscriptions add “image as input” support.
These apps are for cool teens who want to hide things from their parents because their family has trust issues.
Secret Calculator (free on iOS): Secret browser and file vault hidden behind a working calculator app. Requires passcode to unlock. Watch out for less popular apps with very similar names. And don’t bother buying the “pro” version, which hasn’t been updated in years.
Vault Calculator Hide Pictures (free on Android): Similar to Secret Calculator: a secret browser and file vault with cloud backup, hidden behind a calculator app. Supports multiple passwords for specific albums, and can send alerts when a user enters the wrong app passcode.