15 Mental Math Strategies Every Child Should Know
Mental math isn't about memorizing—it's about understanding numbers so well that you can manipulate them flexibly. Here are 15 strategies that develop mathematical thinking.
You don't need to teach all of them at once. Pick the ones that fit your child's grade, practice one for a week, and let your child decide which strategies feel natural.
Why Mental Math Matters
A child who can tell that 48 + 29 must be close to 80 will notice when a calculator slip or a written mistake gives 617. That checking habit is worth as much as the arithmetic itself.
Addition Strategies
1. Counting On
Start from the bigger number and count up.
A common habit is starting from the smaller number: for 3 + 8, counting on 8 times from 3. Show your child that 3 + 8 and 8 + 3 give the same answer, so starting with the bigger number saves work.
2. Making Ten
Combine numbers to make 10 first.
The 5 is split into 2 and 3, because 8 needs 2 more to make 10. This only works smoothly if your child knows the pairs that make ten by heart (1 and 9, 2 and 8, 3 and 7, 4 and 6, 5 and 5). Practice those first. The same idea scales up: 38 + 5 = 38 + 2 + 3 = 43.
3. Doubles
If you know doubles, use near-doubles.
4. Compensation
Adjust numbers to make calculation easier.
The most common mistake here is adjusting in the wrong direction: adding 30 and then adding 1 more, getting 79. Ask, "Did you add too much or too little? So do you need to take some away or put some back?" Another example: 99 + 46 = 100 + 46 − 1 = 145.
5. Left-to-Right Addition
Add the biggest place values first.
This is the opposite of the written method, which starts with the ones, and that's fine. Working left to right means the first number your child gets is already close to the answer.
Subtraction Strategies
6. Counting Back
Start from the larger number and count down.
Watch for the off-by-one error: saying "11, 10, 9" and answering 9. The starting number is not one of the counts. Have your child put up one finger for each number they say after 11.
7. Counting Up (Finding Difference)
Find the distance between numbers.
Counting back 48 steps from 52 would be slow and error-prone. When two numbers are close together, counting up is much faster.
8. Subtract to a Landmark
Go to a friendly number first.
The 17 is split into 13 and 4, because subtracting 13 lands exactly on 40.
9. Same Difference
Add or subtract the same amount from both numbers.
The gap between two numbers stays the same if you shift both by the same amount, like sliding a ruler. This is a lifesaver for problems like 100 − 37: subtract 1 from both to get 99 − 36 = 63, with no borrowing at all.
Multiplication Strategies
10. Skip Counting
Count by the multiplier.
Skip counting is a bridge, not a destination. Once your child skip counts a fact many times, encourage them to try remembering it before they count.
11. Doubling
Double known facts.
Doubling is also the fastest route to the 4s (double, then double again) and the 8s (double three times). For 4 × 7: 2 × 7 = 14, double that is 28.
12. Breaking Apart (Distributive Property)
Split one factor into easier parts.
This works for bigger numbers too: 6 × 23 = (6 × 20) + (6 × 3) = 120 + 18 = 138.
13. Using 10s
Multiply by 10 and adjust.
A common slip is subtracting 9 instead of 7. Talk it through: "Ten sevens is one seven too many, so take away one seven."
Division Strategies
14. Related Multiplication
Turn division into multiplication.
This is why multiplication facts matter so much. A child who knows 7 × 8 = 56 gets four facts for free: 7 × 8, 8 × 7, 56 ÷ 8, and 56 ÷ 7.
15. Halving
Divide by 2 repeatedly for powers of 2.
Dividing by 8 is the same as halving three times, because 2 × 2 × 2 = 8. Halving works for dividing by 2, 4, and 8.
Teaching Mental Math
Daily Practice
A number talk at home takes three minutes. Say one problem, like 25 + 19. Give quiet thinking time with no paper. Then ask for the answer and, more importantly, how they got it. Share your own way too. Someone might do 25 + 20 − 1; someone else might do 24 + 20. Both are right.
Celebrate Multiple Methods
There's no "one right way." Encourage sharing different strategies.
Build on What They Know
Start with comfortable numbers, then extend. If 8 + 5 is easy, try 28 + 5, then 48 + 15.
Make It Fun
If your child gets anxious under time pressure, skip timers entirely. Accuracy and a calm explanation matter more than speed.
Progress by Grade
K-1: Counting on, making 10
2-3: Compensation, doubles, near-facts
4-5: All strategies, larger numbers
6+: Applying strategies to fractions, decimals, percents