Mental Addition Tricks and Shortcuts
With the right strategies, you can add numbers in your head faster than reaching for a calculator. These tricks work because they exploit patterns in our base-10 number system.
Trick 1 – Making Hundreds (or Thousands)
Round one number up to the nearest hundred (or thousand), add, then subtract the rounding adjustment.
67 + 99 → think 67 + 100 − 1 = 166
456 + 998 → think 456 + 1000 − 2 = 1454
Trick 2 – Doubles and Near-Doubles
If the two numbers are close to each other, use the nearest double and adjust.
7 + 8: double 7 = 14, then +1 = 15 or double 8 = 16, then −1 = 15
24 + 25: double 24 = 48, then +1 = 49 or double 25 = 50, then −1 = 49
Trick 3 – Left-to-Right Addition
Add the largest place value first (left to right), then work through smaller values. This gives a running total and is faster than carrying mentally.
347 + 235: 300+200=500, 40+30=70 → 570, 7+5=12 → 582
Trick 4 – Friendly Number Pairs
Look for pairs that total 10, 100, or 1000 and add them first.
4 + 7 + 3 + 6: spot (4+6) = 10 and (7+3) = 10 → 10+10 = 20
Trick 5 – Splitting to Make Easy Numbers
Split one addend to make the other a round number.
48 + 37: split 37 as 32+5 → 48+32=80, then 80+5 = 85
Summary Table
| Trick | Best for | Example |
|---|---|---|
| Making hundreds | Numbers close to 100, 1000 | 67+99=166 |
| Near-doubles | Numbers within 1-2 of each other | 13+14=27 |
| Left-to-right | Multi-digit mental addition | 347+235=582 |
| Friendly pairs | Several single-digit numbers | 4+7+3+6=20 |
| Splitting | One awkward number | 48+37=85 |
Key Takeaways
- Rounding one number and adjusting afterwards is one of the most powerful tricks.
- Near-doubles exploit the doubling facts you already know.
- Spot friendly pairs (that make 10, 100, etc.) when adding multiple numbers.
- Left-to-right addition mirrors how we naturally think about numbers.
Practice Questions
- Use the making-hundreds trick to find 83 + 99.
- Use near-doubles to find 16 + 17.
- Use left-to-right addition to find 254 + 343.
- Find 5 + 9 + 5 + 1 by spotting friendly pairs.
- Use splitting to find 56 + 38.