Percentage Calculator

What Is a Percentage Calculator?

Percentages appear everywhere — mortgage rates, pay rises, sale discounts, exam scores, investment returns. And yet most people hit a wall when asked to calculate something like: what percentage of 340 is 85? Or: if something goes from £47 to £63, what's the percentage increase? There are three distinct percentage calculations, each with its own formula — this calculator handles all of them in one place.

The three core questions: working out X% of a number (what's 17.5% of £840?), finding what percentage one number is of another (45 out of 180 is what percent?), and calculating the percentage change between two values (£200 to £250 is a 25% increase). Most people can do one of these in their head. Few can do all three quickly.

Select the type of calculation using the tabs at the top, enter your numbers, and click Calculate. Results are shown to four decimal places where relevant. Use the Copy Result button to take the answer straight into a spreadsheet or message.

How Do You Use This Percentage Calculator?

Choose your calculation type: find a percentage of a number, find what percentage one number is of another, or calculate percentage change between two values.

1. Select the calculation type: percentage of a number, percentage one value is of another, or percentage change.
2. Enter the first value in the field provided.
3. Enter the second value or percentage.
4. Click Calculate to see the result.
5. Read the answer displayed below the form.
6. Click Reset to start a new calculation.

How Does the Percentage Calculator Formula Work?

The formula used: Percentage = (Part / Whole) × 100

What Are Some Example Calculations?

What is 15% of 200? Answer: 200 × 0.15 = 30. What percentage is 45 of 180? Answer: (45 / 180) × 100 = 25%.

When Should You Use a Percentage Calculator?

Shopping discounts and compounding reductions. A 30% off sign on a £189 jacket means you pay £132.30. But if the jacket is already on sale and they take a further 10% off, you cannot simply add the percentages — that gives the wrong answer. Run each reduction in sequence: 30% off first, then 10% off the reduced price.

Pay rises and investment returns. Your salary went from £31,500 to £34,000 — use the percentage change tab. Your ISA grew from £8,200 to £9,100 — same calculation. Having the precise percentage makes annual review conversations and financial planning considerably more concrete than estimating from memory.

What Do These Terms Mean?

How Do the Options Compare?

What Are the Best Tips to Know?

• Convert a percentage to a decimal by dividing by 100. Move the decimal point two places left.
• Reverse the calculation to check your answer. If 20% of 150 is 30, then 30 / 150 × 100 should return 20.
• Use percentage change — not a simple difference — when comparing two values over time.
• Remember that a 50% decrease followed by a 50% increase does not return to the original value.
• Round percentages to 1 or 2 decimal places for most practical purposes.

What Mistakes Should You Avoid?

• Dividing by the new value instead of the original value when calculating percentage change.
• Forgetting to multiply by 100 after dividing, giving a decimal instead of a percentage.
• Adding successive percentages directly. A 20% rise then a 10% rise is not a 30% rise overall.
• Confusing percentage points with percentages. A rate rising from 5% to 7% is a 2 percentage-point increase but a 40% increase.