% Percentage Calculator
Three ways to calculate percentages — fast and clear.
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Percentages — more useful than they sound
Percentages are everywhere in daily life — tax rates, discounts, interest rates, inflation, opinion polls, nutritional information. Understanding them properly is one of the most practical mathematical skills you can have.
The word "percent" comes from the Latin "per centum" — per hundred. So 37% literally means 37 per 100, or 0.37 as a decimal. The % symbol evolved from the Italian abbreviation "pc" in the 15th century, which gradually morphed through "p/c" and then compressed into the % symbol.
- Percentage of: "What is 15% of $240?" → 240 × 0.15 = $36. Multiply by the decimal form.
- Percentage change: (New − Old) ÷ Old × 100. A price rising from $80 to $100 is a 25% increase. Falling from $100 to $80 is a 20% decrease — note that increases and decreases aren't symmetric.
- The GST trick: To find the pre-GST price from a GST-inclusive price, divide by 1.1 (not subtract 10% — that gives a slightly wrong answer).
- Percentages vs percentage points: An interest rate rising from 2% to 3% is a rise of 1 percentage point, or a 50% increase. These are completely different things — a distinction often mishandled in media reporting.
🦘 Fun fact: Australia's GST was introduced on 1 July 2000 after one of the most contentious political campaigns in Australian history. The Howard government narrowly won the 1998 election on a platform of introducing the tax. Fresh food, healthcare, and education are exempt — making the Australian GST base narrower than most comparable countries.