How to Calculate Percentages: The 4 Cases You Need to Master
thecalculator.tech
9 June 2026 · 4 min read
Discounts, increases, variations and proportions. The four most common types of percentage calculation explained with practical everyday examples.
Case 1: What is X% of a number?
Formula: result = number × (X/100). Example: what is 15% of 340? → 340 × 0.15 = 51. Common uses: calculating a tip, a sale discount, an agent's commission or loan interest.
Case 2: What percentage is A of B?
Formula: % = (A/B) × 100. Example: 45 out of 180 → (45/180) × 100 = 25%. Common uses: calculating market share, pass rates, investment return or what a cost represents as a share of total budget.
Case 3: Percentage change between two values
Formula: change = ((new − old) / old) × 100. If a flat's price rose from €200,000 to €230,000: change = ((230,000 − 200,000) / 200,000) × 100 = +15%. If it fell to €190,000: −5%. Essential for interpreting economic data.
Case 4: Applying an increase or discount
Final price after X% discount: P_final = P_base × (1 − X/100). Final price after X% increase: P_final = P_base × (1 + X/100). Beware of chained percentages: a 20% discount followed by another 20% is not the same as a 40% discount (it is 36% in total).
In tax or financial contexts involving percentages, always verify the calculation with your advisor.
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