Guides/Percentage increase

How to calculate percentage increase

Percentage increase tells you how much a value grew relative to where it started. It is one of the most useful everyday math skills — for price changes, salary reviews, traffic stats, or test scores.

The formula

Percentage increase = ((new value − old value) ÷ old value) × 100

If the result is negative, the value decreased; the absolute value is the percentage decrease. The starting value cannot be zero (division by zero).

Worked examples

1. Price rise: A product goes from $80 to $100. Change = 20; 20 ÷ 80 = 0.25; × 100 = 25% increase.
2. Discount recovery: After a sale, a $40 item returns to $50. (50 − 40) ÷ 40 × 100 = 25% increase from the sale price (not the same as undoing a 20% off).
3. Score improvement: A quiz score moves from 72 to 81. (81 − 72) ÷ 72 × 100 ≈ 12.5% increase.
4. Subscriber growth: A newsletter goes from 1,200 to 1,500 readers. (1,500 − 1,200) ÷ 1,200 × 100 = 25% increase.
5. Decrease example: Inventory falls from 500 units to 425. (425 − 500) ÷ 500 × 100 = −15% (a 15% decrease).

When to use which tool mode

• Increase / Decrease — you have an old and new value (this guide).
• X% of Y — you know the percent and the base (e.g. 15% of a bill). Seepercentage of a number.
• Discount — original price and off-% to get sale price.
• Tip Calculator — restaurant tip and bill split, not general % change.

Common mistakes

• Dividing by the new value instead of the old one.
• Confusing percentage points with percent change (e.g. 10% → 15% is +5 points, but a 50% relative increase).
• Assuming “+20% then −20%” returns to the start — it does not (100 → 120 → 96). See compound two-step increases.
• Comparing different bases (this month vs last year) without stating the baseline clearly.

Try it free

Use ourPercentage Calculator(Increase / Decrease tab) to check any pair of numbers instantly. All math runs in your browser.

Also useful:% of a number·Tip Calculator·How much to tip