How do I calculate 20% of a number?

Multiply the number by 20, then divide by 100. You can also multiply by 0.20.

How do I calculate percentage increase?

Subtract the old value from the new value, divide the result by the old value, then multiply by 100.

How do I subtract a percentage?

Convert the percentage into a decimal and subtract it from 1. For example, subtracting 20% means multiplying by 0.80.

Why is removing VAT different from subtracting 20%?

Because the VAT-inclusive price already contains VAT. At 20%, the net price is the gross price divided by 1.20, and the VAT is the difference between gross and net.

How do I calculate 20% of a number?

Multiply the number by 20, then divide by 100. You can also multiply by 0.20.

How do I calculate percentage increase?

Subtract the old value from the new value, divide the result by the old value, then multiply by 100.

How do I subtract a percentage?

Convert the percentage into a decimal and subtract it from 1. For example, subtracting 20% means multiplying by 0.80.

Why is removing VAT different from subtracting 20%?

Because the VAT-inclusive price already contains VAT. At 20%, the net price is the gross price divided by 1.20, and the VAT is the difference between gross and net.

Percentage Increase vs Percentage Difference

Use the Percentage Increase vs Percentage Difference

Use percentage increase or decrease when one number is clearly the old starting value and the other is the new value. Use percentage difference when you are comparing two numbers and neither number is the obvious starting point.

The simple rule

If the question says “from” one value “to” another value, use percentage change. If the question asks how different two values are, use percentage difference.

Want the correct formula automatically?

The percentage calculator includes modes for percentage increase, percentage decrease and percentage difference.

Use the percentage calculator

The main difference

Percentage increase or decrease is directional. It tells you how much a number has changed compared with its original starting value.

Percentage difference is neutral. It compares two values against their average, so the result is the same whichever number you put first.

Calculation	Best for	Uses a starting value?	Example question
Percentage increase	Growth, rises, price increases	Yes	How much did £100 rise to £125?
Percentage decrease	Falls, reductions, drops	Yes	How much did £125 fall to £100?
Percentage difference	Comparing two values fairly	No	How different are 100 and 125?

What is percentage increase?

Percentage increase measures how much a value has gone up compared with where it started. The old value is the base.

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

Example:
Old value = £100
New value = £125
Increase = £25
£25 ÷ £100 × 100 = 25% increase

This is the right formula for pay rises, bill increases, price rises, investment growth, rent increases and any situation where you have a clear “before” and “after”.

For salary examples, the pay rise calculator is usually more useful because it converts the rise into yearly, monthly and weekly figures.

What is percentage decrease?

Percentage decrease works the same way, but the new value is lower than the old value. The old value is still the base.

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

Example:
Old value = £125
New value = £100
Decrease = £25
£25 ÷ £125 × 100 = 20% decrease

This is why a 25% increase followed by a 20% decrease can bring you back to the original number. The base changed between the two calculations.

Important: a rise from £100 to £125 is a 25% increase, but a fall from £125 to £100 is a 20% decrease. The difference is £25 both ways, but the starting value is not the same.

What is percentage difference?

Percentage difference compares two values against their average. It is useful when neither value is the original or “correct” value.

Percentage difference = |A − B| ÷ ((A + B) ÷ 2) × 100

Example:
A = 100
B = 125
Difference = 25
Average = 112.5
25 ÷ 112.5 × 100 = 22.22%

Use percentage difference for neutral comparisons, such as comparing two quotes, two measurements, two prices from different shops, or two estimates where neither is the original value.

Side-by-side example: 100 and 125

The same two numbers can produce different percentage answers depending on the question being asked.

Question	Formula	Answer
What is the increase from 100 to 125?	(125 − 100) ÷ 100 × 100	25% increase
What is the decrease from 125 to 100?	(125 − 100) ÷ 125 × 100	20% decrease
What is the percentage difference between 100 and 125?	25 ÷ 112.5 × 100	22.22% difference

None of these answers is “wrong”. They answer different questions.

Percentage points are different again

A percentage point is the direct difference between two percentages.

Example:
A rate moves from 20% to 25%.

Percentage point change = 25% − 20% = 5 percentage points
Percentage increase = 5 ÷ 20 × 100 = 25%

This matters with interest rates, tax rates, conversion rates, pass rates and survey results. “Up 5 percentage points” is not the same as “up 5%”.

Everyday examples

Price riseA bill rises from £80 to £92. The increase is £12. £12 ÷ £80 × 100 = 15% increase.

Price dropA price falls from £92 to £80. The decrease is £12. £12 ÷ £92 × 100 = 13.04% decrease.

Two quotesQuote A is £480 and quote B is £540. Percentage difference is £60 ÷ £510 × 100 = 11.76%.

Two shopsOne item costs £2.40 and another costs £2.70. If neither is the original, percentage difference is based on their average.

If the comparison is about shopping value, the unit price comparison calculator may give a clearer answer than percentage difference.

Common mistakes

Using percentage difference for price risesIf a price moved from an old value to a new value, use percentage increase or decrease.

Using the wrong basePercentage change is always measured against the starting value, not the final value.

Confusing percent and percentage pointsA rate moving from 10% to 12% is up 2 percentage points, but up 20% relative to the starting rate.

Adding changes togetherA 20% rise followed by a 20% fall does not return to the starting value, because the base changes.

Which formula should you use?

Your situation	Use this calculation	Related tool
A price rose from old to new	Percentage increase	Percentage Calculator
A price fell from old to new	Percentage decrease	Discount Calculator
You are comparing two quotes	Percentage difference	Percentage Calculator
You are adding or removing VAT	VAT formula	VAT Calculator
You are comparing pack sizes	Unit price	Unit Price Calculator

FAQs

Is percentage difference the same as percentage increase?

No. Percentage increase compares a new value with an old starting value. Percentage difference compares two values against their average.

Why is the percentage increase from 100 to 125 not the same as the decrease from 125 to 100?

Because the base value changes. The increase uses 100 as the base, while the decrease uses 125 as the base.

When should I use percentage difference?

Use percentage difference when you are comparing two values and neither is clearly the original or starting value.

What is the difference between percent and percentage points?

Percentage points measure the direct gap between two percentages. Percent change measures the size of the change relative to the starting percentage.

Can I use percentage difference for discounts?

Usually no. A discount has an original price and a sale price, so percentage decrease or discount percentage is normally the right calculation.

Percentage increase vs percentage difference