🧮 Mental maths in CM1: 7 strategies and a 10-minute daily routine

Mental maths in CM1 takes on a new dimension. Your child is no longer just adding small numbers: now they're expected to work out 25 × 4 in their head, find half of 90 in a flash, or say what 3.5 + 1.5 makes. And if they get stuck, it can bring the whole maths problem to a halt.

The good news is that mental maths isn’t a gift you’re born with. It’s a toolkit: a handful of simple strategies you learn and practise until they become second nature. Here are the key ones for CM1, with clear examples, plus a way to practise them for ten minutes a day—without turning your kitchen into an exam hall.

What your child learns in mental maths in CM1

In CM1, numbers get bigger and more varied. Large whole numbers appear, simple fractions are introduced, and decimals make their debut. Mental maths follows the same path. In practice, your child will work on:

• adding and subtracting two- or three-digit numbers in their head;
• knowing their times tables both ways: 7 × 8 = 56, but also "how many times does 8 go into 56?";
• multiplying and dividing by 10, 100 or 1,000 ;
• using doubles, halves, quadruples and quarters;
• calculating with simple decimals like 0.5, 1.5 or 2.25;
• estimating an approximate answer before calculating.

None of this is mastered in a single evening. What matters is regular practice: little and often, always using the same tools.

The 7 key mental maths strategies for CM1

A child who’s confident with mental maths isn’t necessarily faster than others—they just pick a better route. Faced with 64 + 29, they don’t count up twenty-nine steps; they add 30 and take away 1. Here are the seven tools to have ready by the end of the year.

Don’t try to learn them all at once. Pick one each week, show it with two examples, then let your child try it on five sums. The next week, keep the old one and add a new one: after two months, the toolkit is complete.

The decimal trap: “just add a zero”

This is the most common mistake of the year, and it often comes from a rule heard at home: “to multiply by 10, just add a zero.” It works for 37, which becomes 370. But it doesn’t work at all for 2.5: writing 2.50 doesn’t change its value, while 2.5 × 10 = 25.

The correct explanation is a bit longer, but always true: when you multiply by 10, each digit becomes ten times bigger. Units become tens, tenths become units. Drawing a place value chart (hundreds, tens, units, decimal point, tenths, hundredths) makes it clear: the digits all move one place to the left, but the decimal point stays put.

The same logic works in reverse: 45 ÷ 10 = 4.5 and 300 ÷ 100 = 3. If your child hesitates, help them check with common sense: “If you share 45 sweets between 10 children, each gets more than 4 but less than 5.” The answer 4.5 makes perfect sense.

Simple fractions follow the same sharing idea. To find three quarters of 20, take a quarter (5), then multiply by 3 (15). If this step is tricky, our article on fractions in CM1 explained for parents goes through it all from the start, using slices of cake.

Times tables: the foundation for everything else

Almost all the strategies in the table rely on knowing the times tables. If your child still has to count out 7 × 8 on their fingers, they won’t have enough attention left to choose a clever method. By CM1, the goal is for these facts to be automatic both ways: 7 × 8 = 56 and 56 ÷ 8 = 7 should come to mind just as quickly.

To check your child’s progress, try a simple test: ask ten random multiplications out loud, without a timer. Any that take more than three seconds need more practice. For many children, these are from the 6, 7, and 8 times tables. Print our printable multiplication tables, put them up near your child’s desk, and highlight the tricky products with a marker: the list to work on becomes clear, and it shrinks week by week.

Then, make it fun. Repetition is much easier with a card game or a race against the timer, and you’ll find plenty of ideas in our selection of games for learning multiplication tables.

A 10-minute daily routine at home

When it comes to mental maths, frequency matters more than duration. Ten minutes, four evenings a week, will get you further than an hour on Sunday—which usually ends in tears. Here’s a routine that fits into snack time:

1. Warm-up (2 min). Five quick-fire multiplications: you say “6 × 7”, your child answers, then asks you one in return.
2. Strategy of the week (5 min). Five calculations using the chosen method. For “× 25”, for example: 8 × 25, 12 × 25, 16 × 25, 36 × 25, and 40 × 25 (answers: 200, 300, 400, 900, and 1,000).
3. Timer challenge (2 min). Set a two-minute timer and use a prepared list: your child does as many calculations as possible, notes their score, and tries to beat it tomorrow. Compete only against themselves, never a sibling.
4. Calculation of the day (1 min). A real-life question: “Three cinema tickets at €9 each—how much is that?” (€27).

This short format works even better if you announce it in advance: your child knows exactly when it starts and ends, just like with the Pomodoro method adapted for children. The timer on the table acts as the referee: it says stop, not you.

When your child gets stuck: three common situations

They still count on their fingers. This isn’t a mistake—it’s a sign that some basics, like pairs that make 10 or doubles, aren’t automatic yet. Instead of banning finger-counting, go back to these foundations with the games in our article on mental maths in CE1. They work just as well at age 9 or 10, just a bit faster.

They panic as soon as there’s a timer. Remove the timer. Speed comes as a result of automatic recall, not as a goal in itself. Practise without time limits for two weeks, then reintroduce the timer with a personal score to beat.

They succeed at home but not in class. Often, your child knows each strategy but hasn’t yet learned which one to use. Mix up the calculations: instead of five “compensation” additions in a row, offer a varied list where they must first say “which method?” before calculating. The free printable CM1 exercises from Kidibook provide exactly this mix.

Finally, remember that mental maths skills develop throughout the year. A child who hesitates over 25 × 4 in September may answer instantly by February, as long as those ten minutes a day become a habit rather than a chore.