Mental math strategies for addition
Adding in your head is about splitting numbers into friendly pieces. The main strategies are add the tens then the ones, make the next ten, and round and adjust: 47 + 29 = 47 + 30 − 1 = 76. This page explains each with examples, when to use which, and has a practice set that gives a strategy hint for every answer you miss.
Five mental addition strategies
1. Tens, then ones
46 + 23: 40 + 20 = 60, 6 + 3 = 9, so 69.
2. Add the tens of one number first
58 + 34: 58 + 30 = 88, then + 4 = 92.
3. Make the next ten
67 + 25: 67 + 3 = 70, then 22 more: 92.
4. Round and adjust
47 + 29 = 47 + 30 − 1 = 76. 245 + 99 = 245 + 100 − 1 = 344.
5. Doubles and near doubles
25 + 26 = 25 + 25 + 1 = 51.
Which strategy to use
| One number ends in 8 or 9 | Round and adjust |
| Ones add to more than 10 | Make the next ten |
| No regrouping needed | Tens then ones |
| Numbers are close together | Near doubles |
Mental addition practice
Work each one in your head. Missed ones show the quickest strategy.
Why mental math matters
It builds number sense, makes estimation quick, and gives a way to check written answers. Children who can add 47 + 29 in their head understand place value far better than those who can only line up columns.
Common mistakes
How to teach it at home
Car number plates
Add the first two two-digit numbers you see.
Shopping in your head
Add two prices before reaching the till.
Explain it
Ask “how did you work it out?” and share different ways.
By grade
- Grade 1 (1.NBT.C.4, 1.NBT.C.5): add within 100 using tens and ones; find 10 more and 10 less mentally.
- Grade 2 (2.NBT.B.5, 2.NBT.B.8): add within 100 fluently; mentally add 10 or 100.
- Grade 3 (3.NBT.A.2): fluent within 1,000.
Worksheets and practice
2-digit addition worksheet: printable PDF with an answer key. · Make a fresh test
Last reviewed
Questions parents ask
What are mental math strategies for addition?
Tens then ones, adding tens first, making the next ten, rounding and adjusting, and doubles.
How do you add 9 in your head?
Add 10 and take 1 away: 36 + 9 = 46 − 1 = 45.
How can I help my child get faster at mental math?
Practice a few problems daily, ask them to explain their method, and encourage different strategies.
Is mental math better than writing it down?
Both matter. Mental math builds number sense and checks written work; written methods handle bigger numbers reliably.
When should kids do mental addition?
From grade 1 (tens and ones within 100), building to fluency within 1,000 by grade 3.