Learn the 3-Step Method
1Find the actual change.
New − original: 25 − 20 = 5 cm.
2Divide by the ORIGINAL.
5 out of the original 20 → 5/20.
3Convert to a percentage.
5/20 = 25/100 = 25%.
Worked Example
A phone's price drops from £250 to £200. What is the percentage decrease?
Watch Out! Common Mistakes
Wrong! Divide by the original (20), not the new value: 5/20 = 25%.
Wrong! The 5 cm change must be compared with the original: 5/20 = 25%.
Check the direction! The price went down — it’s a 20% decrease.
⬇ Cheat Sheet
- Change = difference between new and original.
- Divide the change by the ORIGINAL.
- Convert the fraction to a percentage.
- Say whether it's an increase or a decrease.
📖 Continue Your Journey
Quick summary
- Percentage change = change ÷ original, then convert to %.
- The original (starting) amount always goes on the bottom.
- 20 → 25 is a 25% increase; £250 → £200 is a 20% decrease.
- State the direction: increase or decrease.
Frequently asked questions
What is the formula for percentage change?
Change divided by the original amount, converted to a percentage. From 20 to 25: change 5, so 5/20 = 25% increase.
Why divide by the original and not the new amount?
Because the question asks how big the change is compared with where you started. Dividing by the new value gives a different (wrong) answer — the most common error in this topic.
Is percentage change on the KS2 curriculum?
It goes slightly beyond the standard Year 6 objectives, but grammar-school and independent-school 11+ papers use it regularly, so we teach it as a clearly-marked stretch topic.
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