Percentage Calculator

Divide X by Y and multiply by 100. Formula: (X ÷ Y) × 100 = %. For example, 45 is what percent of 180? (45 ÷ 180) × 100 = 25%. This is the most common percentage question — used for test scores, discounts, tips, and ratios.

Subtract the old value from the new value, divide by the old value, then multiply by 100. Formula: ((New − Old) ÷ Old) × 100. A positive result is an increase; negative is a decrease. For example, price goes from $80 to $100: ((100 − 80) ÷ 80) × 100 = 25% increase.

Percentage change compares a new value to an old (reference) value — it has direction (increase or decrease). Percentage difference compares two values with no reference point — it's always positive. Formula for difference: |A − B| ÷ ((A + B) ÷ 2) × 100. Use change for before/after comparisons; use difference when neither value is the 'original'.

Multiply the number by the percentage divided by 100. Formula: Number × (% ÷ 100). For example, 15% of $240 = 240 × 0.15 = $36. This is useful for calculating tips, discounts, taxes, and commissions.

If you know the result after a percentage was applied, divide by (1 + % ÷ 100) for an increase, or (1 − % ÷ 100) for a decrease. Example: a price after 20% increase is $120. Original = 120 ÷ 1.20 = $100. This is useful when a price shown includes tax and you want the pre-tax amount.

10% of any number = move the decimal one place left (10% of 340 = 34). 5% = half of 10%. 1% = move decimal two places left. 20% = double the 10% figure. 15% tip = 10% + half of 10%. 25% = divide by 4. For most real-life estimates, combining these mental shortcuts gets you close enough without a calculator.