Maths SolverA TI-84 costs about $\pounds 100$. Desmos is free in your web browser. The Casio fx-9750GIII is somewhere in the middle. Phone apps range from free to a few pounds. Given that all of these basically do the same job, parents quite reasonably ask why anyone should spend $\pounds 100$ on a piece of plastic from the 1990s.
The honest answer is: usually you should not, but there is exactly one situation where you should, and that situation is “your exam requires it.” The rest of this post is about how to figure out which calculator you actually need, what each option is good for, and the calculator habits I see students develop that quietly cost them marks on exams.
The exam-board picture
| Exam | What you can use |
|---|---|
| UK GCSE Maths (papers 2 & 3) | Any standard scientific calculator. Graphing calculators are technically allowed by some boards but are overkill; most students bring a Casio fx-83 or fx-991. |
| UK A-Level Maths | Calculator with statistical functions and an equation solver, allowed throughout. The Casio fx-991EX (or similar) handles everything you need; a graphing calculator is permitted but not necessary. |
| SAT Math (digital) | Built-in Desmos calculator on the test interface. You can also bring your own approved graphing calculator. Most students just use the built-in Desmos. |
| AP Calculus AB / BC | Approved graphing calculator required (TI-84 series, TI-Nspire, Casio fx-9750GIII, and similar). Used for plotting, finding zeros, computing derivatives at a point, and computing definite integrals numerically. |
| IB Mathematics | Graphing calculator from a small approved list (TI-84 Plus CE, TI-Nspire CX, HP Prime, Casio fx-CG50). Required throughout. |
The pattern: at the highest end of school maths (AP Calc, IB) a graphing calculator is genuinely required. Below that level, a scientific calculator is fine, and most students who buy a graphing calculator never use the graphing functions in a real exam.
A specific common waste of money: parents in the UK buying a TI-84 “to be safe” for a child sitting GCSE. The TI-84 is a US high-school staple and is nearly useless for UK GCSE. A $\pounds 25$ Casio fx-83GTX does everything the GCSE calculator papers ask for, and is the calculator your child’s teacher will assume they have.
What each option is genuinely good for
Standard scientific calculator (Casio fx-83/991, around $\pounds 15$–$\pounds 30$)
Right for: GCSE, A-Level, most undergraduate maths, and any test where graphing functions are not required. Battery lasts years. Reliable. Cheap enough to lose.
Wrong for: anything that needs you to plot a graph in real time, or the AP and IB exams.
Graphing calculator (TI-84 family, Casio fx-CG50, around $\pounds 80$–$\pounds 130$)
Right for: AP Calc, IB Maths, and any course where the syllabus explicitly relies on having a graphing calculator. Useful because it is allowed in the exam. Standardised — everyone in the class will use the same model, so the teacher can give specific button sequences.
Wrong for: any task where Desmos exists and is free. The TI-84 interface is from 1996 and looks it; the screen is tiny; entering an equation involves the worst keyboard ever designed. The reason it survives is exam compliance, nothing else.
Desmos (free, in any browser)
Right for: everything you do at home. Better than any graphing calculator at displaying functions. You can drag sliders to see how a parameter changes a curve in real time, plot multiple functions simultaneously, see them in different colours, type maths naturally instead of pecking at calculator keys. This is the tool to use for homework, for exploring concepts, for checking your hand work.
Wrong for: anything where you cannot use the internet. Almost any exam outside the digital SAT.
Phone apps (Photomath, Wolfram Alpha, Symbolab)
Right for: checking an answer you already think you have, or getting unstuck on a homework problem when no human is available. Wolfram Alpha in particular is genuinely useful for verifying integrals, derivatives, and series.
Wrong for: doing your homework with, in the sense of typing in problems and writing down the answer. This is where students get into real trouble — not because they cheat (though some do) but because they end up unable to do the problems on the exam, where the app is not allowed. The skill the homework was supposed to build never builds.
The habits that quietly cost students marks
A few specific habits I see students fall into when they have a calculator (any kind) at hand. These are silent-killer mistakes; they never feel like they are costing you, until you sit down with a marked exam paper and discover you got most of the questions right but lost easy marks throughout.
1. Reaching for the calculator before thinking
$25\%$ of $80$ is $20$. You should never type that into a calculator; it should fall out of your head before your hand reaches the buttons. Same for tip percentages, simple fractions, doublings, and ten-thousand other small calculations that come up in word problems. The calculator is for the awkward arithmetic, not the routine.
The reason this matters: students who calculator everything also lose the ability to sanity-check their final answer. When the calculator says “the bridge is $4{,}500$ kilometres long,” you should notice that is wrong. If you never compute anything by hand, you lose the feel for whether numbers are plausible.
2. Trusting the calculator’s default mode
Almost every wrong answer in trigonometry is caused by a calculator in radians when the question wanted degrees, or vice versa. Check the mode indicator at the top of the screen every single time before computing a trig function. Make this a literal physical habit; it costs zero seconds and saves dozens of marks across a year.
3. Typing the whole expression, then reading the answer once
Long expressions are easy to type wrong. The fix is to chunk the calculation: compute one piece, write it down, compute the next, combine. The intermediate results give you sanity-check opportunities. The single-typed-expression approach gives you no way to know whether you keyed in $5.7$ when you meant $57$.
4. Storing intermediate results in calculator memory and then trusting them
The calculator’s ANS variable holds the result of the last calculation. It is a great feature, until you do an extra calculation between the two you wanted to chain, and now ANS holds the wrong number. Better: write the intermediate down on paper. Always.
5. Skipping the algebra because the calculator can do it numerically
Using the numerical-solver function on a TI-84 to find roots of an equation is fast. It is also the wrong answer for almost every exam question, because the question wants you to show your method. “I plugged it into the calculator and got $x = 2$” gets zero marks even when the answer is right. Use the calculator to check your hand work, not to replace it.
What to actually buy, depending on your situation
Putting it all together. If you are:
- A UK GCSE student: get the Casio fx-83GTX or fx-991EX for $\pounds 15$–$\pounds 30$. Use Desmos at home for graphing.
- A UK A-Level student: same calculator (fx-991EX is the safer pick because of the equation-solver feature). Desmos at home.
- An AP Calculus student: a TI-84 Plus CE is the standard. The Casio fx-9750GIII is cheaper and equally allowed. Use Desmos at home and the TI in the exam.
- An IB Maths student: TI-84 Plus CE or TI-Nspire CX, both on the IB approved list. Same as above for home use.
- A SAT taker: just use the built-in Desmos calculator on the digital test. You can bring an approved graphing calculator as backup, but most students do not need to.
Total spending if you do this right: $\pounds 25$ for GCSE/A-Level students, around $\pounds 100$ for AP/IB students. Anything more than that is buying features you will not use in a real exam.
One thing the calculator cannot do
None of these tools, free or paid, will help you understand a topic you don’t already get. Calculators speed up the arithmetic once you know what arithmetic to do. They do not tell you that the right method here is integration by parts, or that you should recognise this as a Pythagorean problem, or that the negative root of the quadratic doesn’t make physical sense in this context. That part is on you.
The most common mistake students make about calculators is overestimating how much of the work the calculator does. The calculator is roughly the last $20\%$ of an exam question. The first $80\%$ is reading, setting up the problem, choosing a method, doing the algebra. If you are weak on the first $80\%$, no amount of calculator firepower fixes it.