What is the fastest way to multiply by 9 in your head?

Multiply by 10 and subtract the original number. For 9 x 7: multiply 7 by 10 to get 70, then subtract 7 to get 63. This works for any number: 9 x 23 = 230 - 23 = 207. It is faster and more reliable than trying to recall 9 times tables by rote.

How do you calculate percentages quickly in your head?

Find 10% first by moving the decimal one place left. Then combine: 5% is half of 10%, 15% is 10% plus 5%, 20% is double 10%, 25% is double 10% plus 5%. For harder percentages, use the reversibility trick: X% of Y equals Y% of X. For example, 8% of 25 equals 25% of 8, which is 2.

How do you add large numbers in your head?

Work left to right instead of right to left. For 234 + 178: 200 + 100 = 300, 30 + 70 = 100, so 300 + 100 = 400, then 4 + 8 = 12, so 412. This left-to-right method builds the answer progressively from the most significant digits, which is easier to hold in working memory than carrying from the right.

What are the best tricks for multiplying by 11?

For two-digit numbers: add the two digits and place the result in the middle. For 11 x 43: 4 + 3 = 7, so the answer is 473. For 11 x 67: 6 + 7 = 13, so write 6, carry the 1, get 737. For single-digit numbers, 11 times any digit is simply the digit repeated: 11 x 7 = 77.

Mental Math Tricks to Calculate Faster in Your Head (Works for Any Age)

Calculators are everywhere. Your phone is faster at arithmetic than any human. The skill that matters in daily life is not precision computation but speed estimation: can you quickly verify if a restaurant bill is roughly correct, figure out whether a 40% discount makes something worth buying, or calculate the tip without pulling out a phone?

These tricks make those mental calculations faster, more reliable, and genuinely automatic with practice.

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Test your mental maths speed after reading this

60 seconds. 4 answer choices. Global average is 32 correct. Can you beat it?

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Multiplication Tricks

Multiply by 9: multiply by 10, subtract the original

9 x 7: multiply 7 by 10 to get 70, subtract 7 to get 63.

9 x 23: multiply 23 by 10 to get 230, subtract 23 to get 207.

This works for any number and is faster than trying to recall from rote memory for larger values.

Multiply by 11 (two-digit numbers): add the digits, place in the middle

11 x 43: add 4 and 3 to get 7, place between the original digits to get 473.

11 x 67: add 6 and 7 to get 13. Write 6, add 1 to get 7 in the middle, then 3 at the end: 737.

For single digits, the answer is simply the digit doubled: 11 x 7 = 77, 11 x 4 = 44.

Squares of numbers ending in 5

35 squared: take the tens digit (3), multiply by the next integer (4): 3 x 4 = 12. Append 25. Answer: 1,225.

45 squared: 4 x 5 = 20, append 25 to get 2,025.

75 squared: 7 x 8 = 56, append 25 to get 5,625.

Multiply by 4: double twice

4 x 17: double 17 to get 34, double again to get 68.

4 x 125: double to 250, double to 500.

Addition Tricks

Round and adjust

47 + 38: round 47 up to 50 (adding 3), add 38 to get 88, subtract the 3 you added: 85.

196 + 47: round 196 up to 200 (adding 4), add 47 to get 247, subtract 4: 243.

Left to right addition

234 + 178: start from the left. 200 + 100 = 300. 30 + 70 = 100. Running total: 400. 4 + 8 = 12. Final: 412.

This builds the answer from the most significant digit, which is easier to hold in working memory than carrying from the right.

Make tens: group numbers that sum to 10

Adding 7 + 3 + 8 + 2 + 6: spot the pairs that make 10 first. 7 + 3 = 10. 8 + 2 = 10. Left with 6. Total: 26.

This is especially useful for adding a list of numbers quickly in your head.

Percentage Tricks

Build from 10%

Find 10% by moving the decimal point one place left. Everything else builds from there:

10% of 85 = 8.5
5% of 85 = half of 8.5 = 4.25
15% of 85 = 10% + 5% = 8.5 + 4.25 = 12.75
20% of 85 = double 10% = 17
25% of 85 = 20% + 5% = 17 + 4.25 = 21.25

Reversibility: X% of Y equals Y% of X

Sometimes one direction is much easier to calculate than the other.

8% of 25 is the same as 25% of 8. 25% of 8 = 2. So 8% of 25 = 2.

7% of 50 = 50% of 7 = 3.5.

Choose whichever direction is simpler to calculate mentally.

Percentage	Method	Example: 60
10%	Move decimal left	6
5%	Half of 10%	3
15%	10% + 5%	9
20%	Double 10%	12
25%	Double 10% + 5%	15
50%	Halve the number	30

Division Shortcuts

Divide by 4: halve twice

96 divided by 4: halve 96 to get 48, halve again to get 24.

Divide by 5: multiply by 2, then divide by 10

75 divided by 5: multiply 75 by 2 to get 150, divide by 10 to get 15.

This works because dividing by 5 is the same as multiplying by 0.2, and 0.2 = 2/10.

Divide by 8: halve three times

120 divided by 8: halve to 60, halve to 30, halve to 15.

Divide by 25: multiply by 4, divide by 100

175 divided by 25: multiply 175 by 4 to get 700, divide by 100: 7.

How to Practice

The most effective way to build these into automatic habits is short daily practice rather than long occasional sessions. Two to three minutes per day of deliberate mental calculation produces faster improvement than an hour on weekends.

Natural opportunities to practice: calculating totals at the grocery store before reaching the checkout, verifying restaurant bills mentally, calculating distances and times while travelling, and estimating sale prices before reading the ticket.

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Put these tricks to the test under time pressure

The Math Sprint game starts with single-digit addition and scales up. A perfect warm-up for practising the tricks in this article.

Play Math Sprint

Improving from 32 to 45 correct in 60 seconds, roughly a 40% increase, is achievable for most people within four to six weeks of deliberate daily practice with these methods. The key is replacing slow, rote computation with fast pattern recognition.