Percentage Calculator
A percentage (%) expresses a ratio out of 100. This calculator covers all three common percentage calculations: 'what is X% of a value', 'what percent one value is of another', and 'by what percent a value increased or decreased'.
Examples
Price after a 30% discount
For an item priced at ₩80,000 with a 30% discount, the discount is 80,000 × 0.3 = ₩24,000, so the sale price is ₩56,000.
Test score as a percentage
If you answered 42 out of 50 questions correctly, your score is (42 ÷ 50) × 100 = 84%.
Salary raise percentage
If your salary rises from ₩40,000,000 to ₩44,000,000, the increase is ((44,000,000 − 40,000,000) ÷ 40,000,000) × 100 = 10%.
FAQ
What is the difference between percent (%) and percentage points (%p)?
A percentage point is the arithmetic difference between two percentage values. If an interest rate rises from 2% to 3%, that is a 1%p (percentage point) increase, but as a ratio it is a 50% increase. News reports usually use %p when describing changes in interest rates or approval ratings.
Is a 20% discount followed by a 10% discount the same as 30% off?
No. Discounts apply sequentially. Starting from 100, a 20% discount leaves 80, and an additional 10% discount leaves 72 — a total discount of 28%.
If a value drops 50% and then rises 50%, does it return to the original?
No. A 50% decrease from 100 gives 50, and a 50% increase from 50 gives 75. Because the base value changes, a 100% increase is needed to return to the original.
How do I work backwards to the price before a discount?
Divide the discounted price by (1 − discount rate). For example, if the price after a 30% discount is ₩70,000, the original price is 70,000 ÷ 0.7 = ₩100,000.
What are per mille (‰) and basis points (bp)?
Per mille (‰) means one part per 1,000 (0.1%), and a basis point (bp) is one part per 10,000 (0.01%), commonly used for interest rate changes. A 25bp rate hike means an increase of 0.25%p.
Percentages in everyday life
Percentages appear everywhere: shopping discounts, bank interest rates, loan rates, tax rates, delivery app fees, and investment returns. Once you know the three basic formulas, you can apply them to most situations.
When comparing financial products in particular, check whether interest is simple or compound and whether returns are quoted before or after tax to make an accurate comparison.
Tips to avoid common percentage mistakes
In percent-change calculations, the base value (denominator) is always the 'before' value. Choosing the wrong base can drastically change the result.
Consecutive discounts or changes cannot simply be added — they must be multiplied. A 20% discount followed by a 10% discount is 0.8 × 0.9 = 0.72, i.e. a 28% discount.
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