How to calculate percentage change (increase or decrease)

Percentage change = (new − old) / old × 100. From 80 to 100: (100 − 80) / 80 × 100 = +25%. Going back from 100 to 80 is −20% because the base is different.

Change—

Formula: (New − Old) / Old × 100

Open the full tool: Percentage calculator →

Chart: gain needed to recover a loss

DropGain needed
−5%+5.26%
−10%+11.11%
−15%+17.65%
−20%+25%
−25%+33.33%
−30%+42.86%
−40%+66.67%
−50%+100%
−60%+150%
−75%+300%
−80%+400%
−90%+900%

The base is always the old value

Percentage change is measured against the starting value. That is why 80 → 100 is +25% while 100 → 80 is only −20%. The chart above shows how big the asymmetry gets: after a 50% drop you need a 100% gain to break even.

Percent vs percentage points

When the value itself is a rate or share (say 10% → 12%), the difference is better stated in percentage points: +2 pp, which is a 20% relative increase.

Examples

A price going from 250 to 300 is +20%. Revenue falling from 1.5M to 1.2M is −20%. Followers growing from 1,000 to 1,300 is +30%.

FAQ

How do I calculate a percentage increase?

(New − old) / old × 100. From 250 to 300: 50 / 250 × 100 = +20%.

How do I calculate a percentage decrease?

Use the same formula; the result is negative. From 100 to 85: −15 / 100 × 100 = −15%.

Why don’t −50% and +50% cancel out?

After −50%, 100 becomes 50, and +50% of 50 is only 75. You need +100% to get back to 100.

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