How to Do Division in Your Head Quickly

6 min read · IQ Tester

The easiest way to learn how to do division in your head is to stop thinking of it as long division. Estimate the answer first, then make the problem smaller: halve both numbers when you can, or break the big number into friendly chunks you can divide easily and add the pieces. For 952 ÷ 7, that's 700 ÷ 7 = 100 plus 252 ÷ 7 = 36, so 136.

If number problems like this are where your reasoning slows down, IQ Tester can confirm whether mental arithmetic is your weak spot and drill it every day: Find my weak spots.

Estimate first

Before dividing exactly, get a ballpark. It tells you how many digits the answer has, and it catches wild slips.

• 623 ÷ 7: 630 ÷ 7 = 90, so the answer is a bit under 90. (Exact: 89.)
• 1,480 ÷ 38: about 1,600 ÷ 40 = 40. (Exact: about 38.9.)
• 58 ÷ 6: about 60 ÷ 6 = 10. (Exact: 9 remainder 4, or 9.67.)

The trick is to nudge the numbers so they divide cleanly. You're not looking for close; you're looking for easy and close. On multiple-choice tests, this step alone often gets you the answer, as our timed test taking tips explain.

Halve and halve again

If both numbers are even, you can halve both without changing the answer. Keep going until the problem is easy.

Example: 144 ÷ 6

• Halve both: 72 ÷ 3
• 24

Example: 312 ÷ 8

Dividing by 8 is the same as halving three times.

• 312 → 156 → 78 → 39

Example: 864 ÷ 24

• Halve both: 432 ÷ 12
• Halve both again: 216 ÷ 6
• Halve both again: 108 ÷ 3
• 36

This is the halving method of division, and it's one of the best ways to do double digit division in your head, because the divisor keeps shrinking toward a single digit.

Quick halving rules

• ÷ 4 = halve twice
• ÷ 8 = halve three times
• ÷ 16 = halve four times: 1,248 → 624 → 312 → 156 → 78

Break the number into friendly chunks

When halving doesn't fit, split the number you're dividing into pieces that the divisor goes into cleanly. This is the chunking method of division, and it's the real way to do long division in your head.

Example: 736 ÷ 8

• 720 ÷ 8 = 90
• 16 ÷ 8 = 2
• 92

Example: 952 ÷ 7

• 700 ÷ 7 = 100
• 252 ÷ 7 = 36 (think 210 ÷ 7 = 30, then 42 ÷ 7 = 6)
• 136

Example: 1,035 ÷ 15

• 900 ÷ 15 = 60
• 135 ÷ 15 = 9
• 69

How to pick good chunks

Look for multiples of the divisor that are round or familiar. For 7, that's 70, 140, 210, 350, 700. For 12, it's 120, 240, 360, 600. Take the biggest chunk you can, then deal with what's left. It works the same way as splitting numbers for multiplication in how to multiply in your head.

Chunking is simple on paper. In your head, you're holding 100 while working out 252 ÷ 7, which itself splits into two more pieces. Lots of people drop the first result along the way and can't tell whether the problem is their arithmetic or their memory. IQ Tester's 16 questions separate mental arithmetic from working memory, among seven weak spots, and give you one daily drill, like "Chunk it" or "Estimate first," aimed at the right one. Find my weak spots

Dividing by 5, 25 and 9

A few divisors have shortcuts worth learning by heart.

How to divide by 5 in your head

Double the number, then divide by 10.

• 235 ÷ 5 → 470 ÷ 10 = 47
• 86 ÷ 5 → 172 ÷ 10 = 17.2

How to divide by 25

Multiply by 4, then divide by 100.

• 675 ÷ 25 → 2,700 ÷ 100 = 27
• 850 ÷ 25 → 3,400 ÷ 100 = 34
• 130 ÷ 25 → 520 ÷ 100 = 5.2

Dividing by 9 and the divisibility rule for 9

First, check whether it divides evenly: a number divides by 9 if its digits add up to a multiple of 9. 423 → 4 + 2 + 3 = 9, so yes.

Then chunk with multiples of 9, like 90, 180, 360, 450, 900.

• 423 ÷ 9: 360 ÷ 9 = 40, and 63 ÷ 9 = 7, so 47
• 504 ÷ 9: 450 ÷ 9 = 50, and 54 ÷ 9 = 6, so 56

Bonus: when the digit sum isn't a multiple of 9, it still tells you the remainder. 427 → 4 + 2 + 7 = 13 → 1 + 3 = 4, so 427 ÷ 9 leaves remainder 4.

Decimals and remainders

Dividing with remainders

For whole-number answers, chunk as far as you can, and whatever's left is the remainder.

• 100 ÷ 7: 70 ÷ 7 = 10, 28 ÷ 7 = 4, leaving 2. So 14 remainder 2.

How to do decimal division in your head

Turn remainders into decimals by knowing a few common fractions:

• ÷ 2 leftovers: 1/2 = 0.5
• ÷ 4: 1/4 = 0.25, 3/4 = 0.75
• ÷ 8: 1/8 = 0.125, so 3/8 = 0.375
• ÷ 3: 1/3 ≈ 0.33, 2/3 ≈ 0.67

Examples:

• 7 ÷ 4 = 1 remainder 3 = 1.75
• 17 ÷ 3 = 5 remainder 2 = about 5.67
• 3 ÷ 8 = 0.375

Dividing by a decimal

Multiply both numbers by 10 or 100 until the divisor is whole.

• 50 ÷ 0.25 → 5,000 ÷ 25 = 200
• 4.8 ÷ 0.6 → 48 ÷ 6 = 8

Practice set

Pick your method first, then solve. Answers below.

1. 196 ÷ 4
2. 585 ÷ 5
3. 850 ÷ 25
4. 504 ÷ 9
5. 918 ÷ 6
6. 1,248 ÷ 16
7. 29 ÷ 4 (as a decimal)
8. 7.2 ÷ 0.9

Answers: 1) 49, 2) 117, 3) 34, 4) 56, 5) 153, 6) 78, 7) 7.25, 8) 8

Make mental division feel automatic

Now you know how to do division in your head: estimate first, halve when you can, chunk when you can't, and keep shortcuts for 5, 25 and 9 ready. IQ Tester's 16 questions take about two minutes and show whether mental arithmetic or working memory is holding you back. If it is, your one-a-day 10-minute drill leans toward number problems, and you can retest whenever you like to see the change.

Find my weak spots

FAQ

What is the easiest way to do division in your head?

Estimate first, then shrink the problem. Halve both numbers when they're even, or break the number you're dividing into chunks the divisor goes into cleanly. Add up the chunk answers at the end.

How do you do long division in your head?

Use chunking instead of the written method. Take the biggest round multiple of the divisor you can, divide it, then deal with what's left. For 952 ÷ 7, that's 700 ÷ 7 = 100 and 252 ÷ 7 = 36, so 136.

How do you divide by a two-digit number in your head?

Halve both numbers until the divisor is small, or chunk using multiples of the divisor. For 864 ÷ 24, halving three times gives 108 ÷ 3 = 36. Estimate first so you know roughly what to expect.

How do you divide by 5 or 25 quickly?

To divide by 5, double the number and divide by 10. To divide by 25, multiply by 4 and divide by 100. So 235 ÷ 5 = 47 and 675 ÷ 25 = 27.

How can I get faster at mental division?

Practise a few problems a day, focusing on one method at a time until it's automatic. Knowing your times tables well makes every method faster. Estimating first helps you catch mistakes before they cost you on a test.