Check the permitted list. Then buy the Casio.

The exam rules decide the calculator, not your math teacher and not the salesperson. Start by finding the official approved list for your exam board — most publish one. If your calculator isn’t on it, it doesn’t matter how good it is.

The biggest thing to avoid is a CAS (computer algebra system) or anything with symbolic manipulation. Those are almost always banned. Same with models that have wireless communication or a QWERTY keyboard. What you want is a scientific calculator that’s non-programmable, but can still do fractions, logs, trig, and statistical functions.

The safest bet is the Casio fx-991EX (or the newer fx-991CW) if your board allows it. It’s got a great screen, handles almost everything you’ll see in exams, and is cheap enough to lose. If you’re in the UK, the fx-83GTX or fx-85GTX are the usual go-to. In the US, the TI-30X IIS is the classic trusted option.

One more thing: buy the exact model on the approved list. Don’t buy the “slightly newer version” and assume it’s fine — some boards list specific models. Then practice with it a few times before exam day. You don’t want to be figuring out the fraction button when the clock is running.

A calculator is a tool, not a magic box. Get the one that’s allowed, learn it well, and forget about the rest.