Percentages appear everywhere: discounts, tax rates, interest, tips, grade scores, statistics, financial returns. A percentage calculator solves the most common percentage problems in seconds — no formula memorisation required.
How to Calculate Percentages for Free
iConvertU's Percentage Calculator handles all common percentage calculations.
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- Open iConvertU Percentage Calculator
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The Four Most Common Percentage Calculations
1. What is X% of Y?
Formula: Result = (X ÷ 100) × Y
Example: What is 20% of £85? - (20 ÷ 100) × 85 = 0.20 × 85 = £17
Common uses: Calculating a discount, finding a tip amount, working out VAT or sales tax.
2. X is what percentage of Y?
Formula: Percentage = (X ÷ Y) × 100
Example: 34 is what percentage of 200? - (34 ÷ 200) × 100 = 17%
Common uses: Test scores (34 out of 200 = 17%), market share, proportion calculations.
3. Percentage increase or decrease
Formula: Change% = ((New − Old) ÷ Old) × 100
Example: Price increased from £80 to £96. What is the percentage increase? - ((96 − 80) ÷ 80) × 100 = (16 ÷ 80) × 100 = 20% increase
Example 2: Sales fell from 500 to 425 units. What is the percentage decrease? - ((425 − 500) ÷ 500) × 100 = (−75 ÷ 500) × 100 = −15% (15% decrease)
Common uses: Year-over-year growth, price changes, performance tracking.
4. Original value before a percentage change
Formula: Original = New ÷ (1 + Change%/100)
Example: A coat now costs £120 after a 20% increase. What was the original price? - 120 ÷ (1 + 0.20) = 120 ÷ 1.20 = £100
Example 2 (discount): Item is £85 after a 15% discount. What was the original price? - 85 ÷ (1 − 0.15) = 85 ÷ 0.85 = £100
Common uses: Reverse-calculating original prices, finding pre-tax amounts.
Everyday Percentage Calculations
Restaurant tips
A standard 15–20% tip: - Bill: £45 - 15% tip: (15 ÷ 100) × 45 = £6.75 - 20% tip: (20 ÷ 100) × 45 = £9.00
Quick mental shortcut: 10% of the bill (move decimal one place left), then add half for 15%, or double for 20%.
VAT and sales tax
UK VAT (20%): Price before VAT × 1.20 = Price with VAT - £50 + 20% VAT = £50 × 1.20 = £60
Removing VAT from a price: £60 ÷ 1.20 = £50 (original price before VAT)
US sales tax varies by state (0% to over 10%). Find the pre-tax price: Total ÷ (1 + tax rate).
Discounts
Calculating the discounted price: - Original: £120, discount: 25% - Discount amount: (25 ÷ 100) × 120 = £30 - Sale price: 120 − 30 = £90
Quick formula: Sale price = Original × (1 − discount%) - 120 × (1 − 0.25) = 120 × 0.75 = £90
Interest rates
Simple interest: Interest = Principal × Rate × Time - £1,000 at 5% per year for 3 years: 1000 × 0.05 × 3 = £150 interest
Compound interest: A = P × (1 + r/n)^(nt) For most savings accounts: A = 1000 × (1 + 0.05)^3 = £1,157.63
Grade percentages
Score: 68 out of 85 total marks. Percentage grade: - (68 ÷ 85) × 100 = 80%
Percentage vs Percentage Points
This distinction matters when discussing changes to percentages:
Percentage change: Describes how a value changes relative to its original value.
Percentage points: Describes the absolute arithmetic difference between two percentages.
Example: Interest rate rises from 3% to 5%. - That's an increase of 2 percentage points - But a percentage increase of (5−3)/3 × 100 = 66.7%
This confusion is often exploited in financial and political communication: "our interest rate only increased by 2 percentage points" sounds smaller than "our interest rate increased by 66.7%".
Frequently Asked Questions
What is the difference between percent and percentage? "Percent" (%) is used with a specific number: "20 percent". "Percentage" is used without a specific number: "a large percentage of the population". In everyday use the distinction is often ignored.
How do I calculate percentage off quickly in my head? For common discounts: find 10% (move the decimal one place left), then scale. 20% = double of 10%. 25% = half of 50% = quarter of the total. 15% = 10% + half of 10%.
What is a basis point? In finance, 1 basis point = 0.01% = one hundredth of a percentage point. Used to describe small changes in interest rates and yields: "the Bank raised rates by 25 basis points" = 0.25%.
Is the calculator free? Yes. iConvertU Percentage Calculator is completely free. No account, instant results.
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