How to Use Our Percentage Calculator
Our percentage calculator lets you work out percentages of any number, find percentage increases or decreases, and figure out what percentage one number is of another — all without reaching for a calculator or wrestling with a spreadsheet. Percentages come up constantly in everyday money decisions: discounts at the shops, salary rises, investment returns, savings targets. This guide walks you through exactly how to use our percentage calculator to get accurate results in under a minute.
What Is a Percentage and Why It Matters
A percentage is a way of expressing a number as a fraction of 100. The word comes from the Latin "per centum" — literally "for every 100". So 50% means 50 out of 100, or one half. 25% is one quarter. 200% is twice the original amount.
Percentages appear everywhere:
- Shopping: A 30% discount, or VAT at 20% added to a bill.
- Salary: A 5% annual pay rise, a 10% pension contribution, or a bonus as a percentage of your base.
- Savings: What percentage of your income goes to rent, or what percentage of your savings goal you've hit.
- Growth: Your savings returning 7% per year, or house prices rising 8% in a year.
- Comparisons: "Energy bills rose 12% this year" or "investments grew 15% over two years".
The percentage calculator does the maths instantly. No formulas to remember, no mental arithmetic required.
Using the Calculator: Step by Step
The calculator offers three calculation types:
- Percentage of a number: "What is 20% of £500?" → Answer: £100.
- Percentage change: "If something was £100 and is now £120, what's the change?" → Answer: 20% increase.
- Find the percentage: "£25 is what percentage of £200?" → Answer: 12.5%.
Pick the one that matches your question. (If you're not sure which one, the descriptions under each option are clear — and if you pick the wrong one, the breakdown will show you.) Enter your numbers (no £ signs needed), hit calculate, and review the breakdown. The breakdown shows why the answer is what it is. Then try adjusting one number and recalculating to see how the result changes — this "what-if" analysis helps you understand which factors matter most.
The Three Calculation Types Explained
Type 1: What is X% of Y?
The most common calculation. You know the percentage and the number, and you want the result.
Example: A coat costs £240 and there's a 15% discount. How much do you save?
- Percentage: 15
- Number: £240
- Result: £36
You pay £204 (£240 minus £36). Formula: (percentage ÷ 100) × number.
Type 2: What percentage change is this?
You have an old value and a new value. Useful for tracking growth, inflation, salary changes, and investment returns.
Example: Your energy bill was £1,200 last year and £1,350 this year. What's the increase?
- Original: £1,200
- New: £1,350
- Result: 12.5% increase
Formula: ((new minus old) ÷ old) × 100. For longer-term growth, try our percentage change calculator.
Type 3: X is what percentage of Y?
You have two numbers and want to know what percentage one is of the other. Useful for progress towards a goal or understanding proportions.
Example: You've saved £4,500 towards a house deposit of £15,000. What percentage is that?
- Part: £4,500
- Whole: £15,000
- Result: 30%
Formula: (part ÷ whole) × 100.
Real-World Examples
Scenario 1: Your salary rise
You earn £32,000 a year and you've been offered a 4% pay rise. What's your new salary?
Using the calculator:
- Calculation type: "Percentage of a number"
- Percentage: 4
- Number: 32,000
- Result: £1,280
Your new salary is £32,000 + £1,280 = £33,280. But that's gross. Use our salary calculator to see your exact take-home after tax and National Insurance.
Scenario 2: Investment returns
You invested £10,000 in a stocks ISA three years ago. It's now worth £12,500. What's your return?
Using the calculator:
- Calculation type: "Percentage change"
- Original: £10,000
- New: £12,500
- Result: 25% increase
Your money grew 25% over three years — roughly 7.7% per year. Try our investment calculator to explore different amounts and time horizons.
Scenario 3: A discount
A jacket normally costs £120 and it's on sale at 35% off. What's the sale price?
Using the calculator:
- Calculation type: "Percentage of a number"
- Percentage: 35
- Number: £120
- Result: £42 (the discount)
You pay £120 minus £42 = £78.
Advanced Tips
Tip 1: Use it to compare offers If you're comparing a 6% pay rise to a flat £2,000 bonus, plug your current salary into the percentage calculator to see which is better.
Tip 2: Chain calculations for multi-year growth If your savings grew 8% one year and 12% the next, don't just add them. Use the calculator twice — once for each year on the updated amount.
Tip 3: Understand percentage increases vs. multipliers 100% increase = something doubled (2×). 50% increase = 1.5×. 200% increase = 3×. A "300% growth" headline means 4× the original.
Tip 4: Work backwards If you know the result and percentage but need the original: £2,400 is a 15% bonus. Original = £2,400 ÷ 0.15 = £16,000.
Tip 5: Budget tracking If you spend £800/month on rent from £2,500 take-home, that's 32% of your income. Knowing these percentages helps you see where your money goes. Use our savings goal calculator to track progress towards targets.
Frequently Asked Questions
Q: Is the calculator accurate?
Yes, it uses standard formulas. It's accurate for planning. For tax calculations, verify with HM Revenue & Customs or a professional.
Q: What if I get an unexpected result?
Double-check your inputs. A common mistake is using the wrong calculation type. Try working backwards as a cross-check: if 20% of 500 is 100, then 100 is what percentage of 500? (Answer: 20%.)
Q: Can I use this for tax?
You can estimate rough figures. For exact take-home pay, use our salary calculator. For investment gains and tax questions, consult HMRC's guidance or a tax professional.
Q: What's the difference between percentage points and percentages?
If interest rates go from 3% to 5%, that's a 2 percentage point increase. But it's a 67% relative increase to the rate itself (2 ÷ 3 = 0.67). News reports usually mean percentage points when they say "base rates rising by 0.5%". Keep this distinction in mind when comparing rates.
Q: Can I save my calculations?
Yes. Create a free account on SimpleCalc and your calculations are stored. You can revisit them, adjust inputs, and track changes over time — useful for monitoring investments or savings targets.
Q: What if my situation is unusual?
Our calculator covers common cases. For complex scenarios (like compound percentage changes over many years), run multiple calculations or use a spreadsheet. Start with the percentage calculator, then expand from there.
Q: Can I share a calculation?
Yes. Copy the URL after you've calculated a result and share it. Anyone you send it to will see your inputs and results — useful when discussing financial decisions with a partner or advisor.
Next Steps
You now know how to use the percentage calculator. Try these related tools:
- For salary decisions, our salary calculator shows your exact take-home after tax.
- For investment returns, our investment calculator factors in growth over time.
- To track savings progress, use our savings goal calculator.
- For longer-term growth, try our percentage change calculator for tracking growth.
- To compare buying vs. renting, use our rent vs buy calculator.
- To see your full financial picture, try our net worth calculator.
The percentage calculator is the foundation for financial decisions. Start with a question you have right now, plug in your numbers, and see what you discover.