Percentage Change Calculator
Percentage change — the relative increase or decrease between two values — is one of the most important metrics in business analysis, finance, and reporting. It tells you not just how much something changed in absolute terms, but how large that change was relative to where it started. A £5 price increase means something very different when the original price was £10 versus £100. Percentage change captures this proportional relationship and makes comparisons meaningful.
This calculator works in two modes. The first finds the percentage change between two numbers — enter the original (old) value and the new value to see the exact percentage increase or decrease. The second applies a known percentage change to a starting value — enter the original value and the change percentage to calculate the resulting figure. A 25% increase from £80 gives £100; this can be immediately verified by running the reverse calculation in the first mode. Both directions show the formula used.
Percentage change is used in virtually every type of business and financial analysis: year-on-year revenue growth, price movement tracking, salary review calculations, portfolio performance measurement, and comparing results across reporting periods. An important distinction to understand is the difference between percentage change and percentage points — a variable moving from 4% to 6% is a 2 percentage-point increase but a 50% relative change. Confusing these two measures is one of the most common errors in financial communication and reporting.
Formula
Percentage Change = ((New − Old) ÷ |Old|) × 100 New Value = Old Value × (1 + Change% ÷ 100)
To find the percentage change, subtract the old value from the new, divide by the absolute value of the old, and multiply by 100. A positive result means increase; negative means decrease. To apply a change, multiply the original value by (1 + rate).
Worked Examples
Frequently Asked Questions
What is the formula for percentage change?▾
Percentage change = ((New Value − Old Value) ÷ |Old Value|) × 100. A positive result means the value increased; a negative result means it decreased. Always divide by the original (old) value, not the new one — dividing by the wrong value is the most common formula error.
How do I calculate a percentage increase?▾
Subtract the original value from the new value, divide by the original, and multiply by 100. For example, from 80 to 100: (100 − 80) ÷ 80 × 100 = 25% increase. Alternatively, the new value is 125% of the original (100 ÷ 80 = 1.25), confirming a 25% increase.
How do I calculate a percentage decrease?▾
The formula is the same as for a percentage increase — the result will simply be negative when the new value is lower. For example, from 100 to 75: (75 − 100) ÷ 100 × 100 = −25%. This indicates a 25% decrease. The magnitude of a decrease and a subsequent increase are not symmetric: a 25% decrease followed by a 25% increase returns you to only 93.75% of the original, not 100%.
What is the difference between percentage change and percentage points?▾
Percentage change is relative: if a rate moves from 20% to 25%, the percentage change is (25 − 20) ÷ 20 × 100 = 25%. Percentage points measure the absolute arithmetic difference: 25% − 20% = 5 percentage points. These are very different quantities and are often confused. In financial reporting, it is critical to specify which measure is being used.
How do I reverse a percentage change to find the original value?▾
If you know the current value and the percentage change, divide by (1 + change ÷ 100). For example, a value is now £120 after a 20% increase: £120 ÷ 1.20 = £100 original. For a decrease, divide by (1 − rate ÷ 100): if a value is now £80 after a 20% decrease, the original was £80 ÷ 0.80 = £100.
How is percentage change different from ROI?▾
ROI (Return on Investment) uses the same percentage change formula but applied specifically to financial returns: (Gain − Investment) ÷ Investment × 100. Percentage change is the general-purpose version of the same calculation applied to any two values. When the 'old value' is your initial investment and the 'new value' is the total return, percentage change equals ROI.
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All calculations are for informational purposes only. They should not replace professional financial, tax, or legal advice. Always consult a qualified professional for decisions affecting your finances or business.