Mental maths tests for trading interviews: why they matter and how to get faster

Many trading firms put candidates through a timed arithmetic test early in the process. Lots of questions, a short clock and no calculator. It can feel oddly basic for a job that involves serious maths. Why would anyone care whether you can do 97 × 96 in your head?

The answer says a lot about what traders actually do all day.

Why the test exists

A trader quoting prices doesn't have time to open a spreadsheet. They need to know roughly what a position is worth, what a fill means for their risk and whether a price is off by a little or a lot. All of that runs on quick arithmetic done while something else is going on.

So the test isn't checking whether you know how to multiply. It's checking whether arithmetic is cheap for you. If every sum takes effort there's nothing left over for judgement. If sums are automatic your attention goes where it's needed.

Accuracy first, then speed

The most common mistake is rushing. Under a clock it's tempting to guess, but a fast wrong answer is worse than a slower right one. On a desk a wrong number costs money. And if a test marks errors down, guessing can lower your score rather than raise it.

The aim is to be fast because you're accurate, not fast instead of it. Speed comes from having a method ready for each type of question, not from pushing harder.

Five shortcuts worth knowing

None of these are tricks you'll forget. They're ordinary algebra that turns a hard sum into an easy one.

It also pays to know some fractions as decimals by heart. Eighths (1/8 = 0.125, 3/8 = 0.375) and sevenths (1/7 ≈ 0.143) come up often in probability. Knowing them saves you dividing from scratch.

Estimate before you calculate

Before working out an answer, take half a second to guess its size. 97 × 96 is a bit under 100 × 100, so somewhere just over 9,000. If your working gives 8,312 or 93,120 you'll know at once that something slipped.

How to practise

Short daily sessions beat long weekly ones. Ten minutes a day of mixed questions, with a timer running, builds the automatic recall the test is looking for. Track two numbers: how many you got right and how long it took. Push for speed only once your accuracy is steady.

Then practise doing arithmetic while talking. In a live interview you'll often need to work out a number in the middle of explaining something else, such as an expected value or a market you're quoting. That's harder than a silent test and it's closer to the real job.