Percentage Calculator

Percentage Calculator

Charlotte Green
Charlotte Green
updated on 7 March 2025
Table of Contents
  • What is a Percentage?
  • How to Calculate a Percentage?
  • How is a Percentage Used?
  • How do I calculate a percentage increase?
  • How do I calculate a percentage decrease?
  • How do I calculate a reverse percentage?
  • How to Convert a Percentage to a Grade?
  • How to Calculate a GPA from a Percentage?

Percentages are a quick way to compare numbers, track changes, and understand proportions. Whether you’re working out a sale discount, checking your exam scores, or comparing mortgage rates, understanding percentages makes life easier.

But what is a percentage? How do you calculate it? You can do it manually with a simple formula or use our online percentage calculator to get results in seconds — perfect for when you need a quick answer without the maths! Read on to find out more in our detailed guide.

What is a Percentage?

A percentage expresses a number as a fraction of 100. It’s often used to compare proportions, measure changes, and analyse statistics. You’ll see percentages in finance, retail, education, and health data.

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What is a percentage?

If you scored 85% on your GCSE Maths exam, it means you got 85 out of 100 marks correct.

How to Calculate a Percentage?

To calculate a percentage, use this simple formula:

Percentage = (Part​ ÷ Total) × 100

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For example

You have 10 biscuits, and you eat 4. Want to find out what percentage you ate?

  • Divide the part (biscuits eaten) by the total (all biscuits): 4 ÷ 10 = 0.40
  • Multiply by 100: 0.40 × 100 = 40%

So, you ate 40% of the biscuits.

How is a Percentage Used?

Percentages are a part of everyday life, helping us understand proportions, compare values, and make smarter financial decisions. Here are some real-life examples of how percentages are used:

Shopping: Discounts & Sales

Imagine you find a coat on sale for 25% off its original price of £100. To find your savings:

  • Multiply the discount percentage by the original price: 100 × 0.25 = 25
  • You save £25, and the new price is £75.

Sales and discounts use percentages to show how much you save at checkout.

Finance: Mortgage & Savings Rates

Percentages are essential in banking, especially for interest rates on mortgages and savings accounts.

If your bank offers 3% interest on a £5,000 savings account:

  • Multiply your balance by the interest rate: 5000 × 0.03 = 150
  • You earn £150 in interest for the year.

The higher the percentage, the more you earn on savings!

Health & Nutrition: Food Labels

Ever checked a food label and seen “10% sugar” on a fruit juice bottle? This means that in 100ml of juice, 10ml is sugar.

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For example

If the bottle contains 500ml of juice:

  • Multiply the total weight by 10% (0.10): 500 × 0.10 = 50
  • So, the bottle has 50ml of sugar in total.

Understanding percentages in nutrition helps you make healthier choices. From calculating tips at restaurants to tracking sports statistics, percentages are everywhere!

How do I calculate a percentage increase?

A percentage increase tells you how much something has grown compared to its original value.

Formula:

Percentage Increase = ((New Value − Old Value​) ÷ Old Value) × 100

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How do I calculate a percentage increase?

Your electricity bill was £80 last month, but this month it’s £100.

  • Find the difference: 100 − 80 = 20
  • Divide by the original value: 20 ÷ 80 = 0.2520 ÷ 80 = 0.25
  • Multiply by 100: 0.25 × 100 = 25%

Your electricity bill increased by 25%.

How do I calculate a percentage decrease?

A percentage decrease tells you how much something has reduced from its original value.

Formula:

Percentage Decrease = ((Old Value − New Value​) ÷ Old Value) × 100

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How do I calculate a percentage decrease?

A mobile phone originally cost £600, but now it’s on sale for £450.

  • Find the difference: 600 − 450 = 150
  • Divide by the original price: 150 ÷ 600 = 0.25
  • Multiply by 100: 0.25 × 100 = 25%

The phone is now 25% cheaper.

How do I calculate a reverse percentage?

A reverse percentage helps you find the original value before a percentage change.

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For example

You bought a laptop for £900 after a 10% discount, but you want to know the original price.

Since £900 is 90% of the original price:

Divide by 0.90: 900 ÷ 0.90 = 1000

So, the original price before the discount was £1,000.

How to Convert a Percentage to a Grade?

In the UK, GCSE and A-Level grades are sometimes converted to percentages for UCAS applications.

PercentageGCSE GradeA-Level Grade
90-100%9 (A*)A*
80-89%8 (A)A
70-79%7 (A)B
60-69%5-6 (B/C)C
Below 60%4 or lowerD/E
Percentage to grade conversion examples
90-100%
GCSE Grade
9 (A*)
A-Level Grade
A*
80-89%
GCSE Grade
8 (A)
A-Level Grade
A
70-79%
GCSE Grade
7 (A)
A-Level Grade
B
60-69%
GCSE Grade
5-6 (B/C)
A-Level Grade
C
Below 60%
GCSE Grade
4 or lower
A-Level Grade
D/E
Percentage to grade conversion examples
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For example

If you scored 85% in Maths, that’s equivalent to an A (Grade 8-9 in GCSE or an A at A-Level).

How to Calculate a GPA from a Percentage?

In the UK, students don’t use GPA like in the US, but universities may convert grades to a GPA scale for international applications.

PercentageUK GradeApproximate GPA (US Scale)
70%+First (1st)4.0
60-69%Upper Second (2:1)3.3 - 3.7
50-59%Lower Second (2:2)2.7 - 3.0
40-49%Third (3rd)2.0 - 2.5
Below 40%Fail0.0 - 1.5
Percentage to GPA calculation example
70%+
UK Grade
First (1st)
Approximate GPA (US Scale)
4.0
60-69%
UK Grade
Upper Second (2:1)
Approximate GPA (US Scale)
3.3 - 3.7
50-59%
UK Grade
Lower Second (2:2)
Approximate GPA (US Scale)
2.7 - 3.0
40-49%
UK Grade
Third (3rd)
Approximate GPA (US Scale)
2.0 - 2.5
Below 40%
UK Grade
Fail
Approximate GPA (US Scale)
0.0 - 1.5
Percentage to GPA calculation example
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For example

If your university grade is 65%, it’s a 2:1 (Upper Second), roughly equal to a 3.5 GPA in the US.

Charlotte Green
Charlotte Green
HelloSafe
Charlotte is a finance content specialist with a sharp analytical mind and a strong academic background. She holds a degree in Philosophy, Politics and Economics (PPE) from the University of Oxford and a Master’s in Behavioural Economics from the London School of Economics. Her academic training gave her the tools to make sense of complex financial systems—and to explain them in a way that’s both smart and relatable. Before joining HelloSafe, Charlotte worked in editorial roles for financial media and strategy firms, where she focused on personal finance, digital banking, and policy analysis. She is passionate about helping people make informed decisions about their money, especially in an age where the financial landscape is changing fast. At HelloSafe, she covers key topics such as insurance, tax, utilities, credit and budgeting tools. Her mission: provide clear, honest and actionable insights that empower readers to take control of their financial lives with confidence.

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