Five percentage formulas in one page — instant answers as you type.
Percentages appear in virtually every area of daily life: tax calculations, bank interest rates, salary negotiations, exam scores, discount shopping, and investment returns. Knowing the correct formula for each situation prevents costly errors — particularly the common mistake of applying GST percentages to the wrong base, or miscalculating successive discounts.
① What is X% of Y — the fundamental percentage: multiply Y by X divided by 100. Used for calculating GST amount on a price, finding what a tip percentage costs, or determining how much of a budget a line item represents.
② X is what % of Y — finds the percentage relationship: divide X by Y and multiply by 100. Used for exam scores, completion rates, and market share calculations.
③ Percentage Change — finds how much something increased or decreased: subtract the old value from the new, divide by the old value, multiply by 100. Negative results indicate a decrease. Used for salary hike percentages, inflation rates, and revenue growth.
④ Add X% (Tax/Markup) — adds a percentage to a base value: multiply by (1 + X/100). Used to calculate GST-inclusive prices or add a profit margin to cost price.
⑤ Subtract X% (Discount) — removes a percentage from a value: multiply by (1 − X/100). Used to apply discounts, calculate after-tax take-home salary, or find sale prices.
One of the most common financial errors is reverse-calculating tax incorrectly. If a product costs ₹1,180 including 18% GST, the tax is NOT 18% of ₹1,180. The correct method: divide ₹1,180 by 1.18 = ₹1,000 base price, and ₹180 is the GST. Use formula ⑤ to subtract the tax — enter ₹1,180 and 18% to see the correct base value.