Mental subtraction strategies

Five tricks for subtracting in your head: tens first, count up, round and adjust, same difference and back to ten.

Why learn to subtract in your head?

Column subtraction always works, but it is slow for problems like 62 − 59 or 300 − 198, and it hides how numbers relate. Mental strategies are quicker and build number sense, and they give a fast check on written answers.

The trick is to look at the numbers first and choose. Different numbers suit different strategies, and children who choose well rarely need a pencil for 2-digit subtraction.

See it: pictures to draw with your child

Copy these onto paper or a whiteboard. A quick sketch makes the idea concrete before any written method.

4050607080−10−10−10−27442
Tens first: 74 − 32 is three jumps back of 10, then 2.
50515253545556575859606162636465+3+2
Count up: 57 to 60 is 3, 60 to 62 is 2, so 62 − 57 = 5.
5060708090−308353
Round and adjust: 83 − 30 = 53, then add 1 back because we took 1 too many: 54.

The five strategies

StrategyExampleBest when
Tens first74 − 32: 74 − 30 = 44, 44 − 2 = 42No regrouping needed, or small ones
Count up62 − 57: 57 → 60 is 3, 60 → 62 is 2, total 5The two numbers are close
Round and adjust83 − 29: 83 − 30 = 53, add 1 back = 54Taking away 9, 19, 29, 98…
Same difference71 − 38 = 73 − 40 = 33Moving both numbers makes it easy
Back to ten53 − 8: 53 − 3 = 50, 50 − 5 = 45Taking a 1-digit number across a ten

Picture it on a number line

Jump back in tens, then ones. Switch to count up for close numbers.

The same-difference trick

If you add the same amount to both numbers, the difference does not change. Picture two children, aged 7 and 10: in 5 years they will be 12 and 15, still 3 years apart.

So 71 − 38 is the same as 73 − 40 (add 2 to both), and 73 − 40 = 33 is easy. For 300 − 198, add 2 to both: 302 − 200 = 102.

You can also take the same amount from both. 500 − 178 is the same as 499 − 177, which needs no regrouping: 322.

How to choose

There is no single right method. Ask your child “how did you do it?” and celebrate different routes to the same answer.

Building the habit

Mental strategies grow from the facts within 20. A child who knows 13 − 8 = 5 instantly can do 63 − 8, 130 − 80 and 1,300 − 800 just as quickly. So keep a few minutes of fact practice going while learning these strategies.

Start with one strategy a week, using numbers that suit it. Then mix problems and ask your child to choose. Writing the jumps on a quick number line is fine at first; the aim is to need the paper less and less.

Quiz: subtract in your head

Pick a strategy for each one. The hint shows a quick way.

Where this fits: subtraction step by step

  1. What is subtraction
  2. Subtraction within 10
  3. Counting back
  4. Subtraction on a number line
  5. Counting up
  6. Fact families
  7. Make 10 subtraction strategy
  8. Subtraction within 20
  9. Subtracting tens and hundreds
  10. 2-digit subtraction
  11. Subtraction with regrouping
  12. 3-digit subtraction
  13. Subtracting across zeros
  14. Mental subtraction strategies (this page)
  15. Checking subtraction with addition
  16. Missing number subtraction
  17. Estimating differences
  18. Multi-digit subtraction
  19. Subtraction word problems

What to say to your child

A short script for teaching it the first time. Pause after each line and let your child do the next step.

  1. “What is 62 − 59? Would you use columns?” (Maybe.)
  2. “Look how close the numbers are. Count up from 59.” (60, 61, 62: three!)
  3. “Now 83 − 29. 29 is nearly 30. Take 30.” (53.) “We took 1 too many, so add it back.” (54!)
  4. “And 74 − 32?” (Tens first: 44, then 42.)
  5. “Which trick did you like best? There is more than one right way.”

More worked examples

Example 1: tens first: 86 − 43

Take the tens: 86 − 40 = 46. Then the ones: 46 − 3 = 43. So 86 − 43 = 43.

Example 2: round and adjust: 152 − 98

98 is nearly 100. 152 − 100 = 52. We took 2 too many, so add 2: 54.

Example 3: same difference: 61 − 27

Add 3 to both: 64 − 30 = 34. So 61 − 27 = 34.

Example 4: back to ten: 42 − 7

42 − 2 = 40, then take the other 5: 35.

Practice questions (answers below)

Ask these out loud or write them down. Check each answer, and ask “how did you get that?” for one or two.

  1. 55 − 23
  2. 71 − 68
  3. 64 − 19
  4. 90 − 47
  5. 43 − 8
  6. 200 − 97
  7. 81 − 39
  8. 500 − 248
  9. A toy costs 79 rupees. You pay with 100. How much change?
  10. Stretch: 1,000 − 999 and 1,000 − 1
Show the answers
  1. 32
  2. 3
  3. 45
  4. 43
  5. 35
  6. 103
  7. 42
  8. 252
  9. 21 rupees
  10. 1 and 999

Common mistakes

Adjusting the wrong way83 − 29: takes 30, then takes 1 more and gets 52.Fix: you took away 1 too many, so give it back: 54.
Changing only one number71 − 38: adds 2 to 38 only and gets 31.Fix: for the same difference, change both numbers by the same amount: 73 − 40.
Counting up wrongly62 − 57: counts 57, 58 … 62 as 6.Fix: count the jumps between numbers: 57 to 62 is 5.

How to teach it at home

Change at the shop

Ask how much change from 100 for a price like 64: count up.

Ages

Ask how many years between two family members’ ages.

One strategy a week

Pick one trick and use it for every subtraction that week.

By grade

More for each grade: Grade 2 math and the CBSE class 2 maths guide; Grade 3 math and the CBSE class 3 maths guide; Grade 4 math and the CBSE class 4 maths guide.

Worksheets and practice

2-digit subtraction worksheet, page 1

2-digit subtraction worksheet: printable PDF with an answer key. · Make a fresh test

Subtraction practice · subtraction speed test · subtraction chart · subtraction for kids

Last reviewed

Questions parents ask

What are mental subtraction strategies?

Ways to subtract in your head without writing columns: tens first, count up, round and adjust, same difference and back to ten.

What is the easiest way to subtract in your head?

It depends on the numbers. Close numbers: count up. Numbers like 29 or 98: round and adjust. Otherwise take the tens first, then the ones.

What is the same difference strategy?

Adding or taking the same amount from both numbers keeps the difference the same. 71 − 38 = 73 − 40 = 33.

What grade learns mental subtraction?

Grade 2 subtracts within 100 using place-value strategies (2.NBT.B.5), and grade 3 within 1,000 (3.NBT.A.2).

Should my child still learn column subtraction?

Yes. Mental strategies are faster for many problems, and the written method handles any size. Children need both.