Percentage Formulas You Actually Use in Daily Life

Percentages show up constantly in daily life — discounts while shopping, marks in exams, salary hikes, price changes — but most people only remember one percentage formula and try to force every situation into it. Here are the actual distinct calculations you need.

Finding a percentage of a number

The most basic case: what is X% of Y? Multiply Y by X and divide by 100. For example, 20% of ₹2,500 is (2500 × 20) / 100 = ₹500. This is the calculation behind most discount and tip scenarios.

Finding what percent one number is of another

This is the exam-marks scenario: if you scored 78 out of 90, what percentage is that? Divide the part by the whole and multiply by 100: (78 / 90) × 100 = 86.7%. People often get this backwards by dividing the wrong number into the other.

Percentage increase or decrease

This is the one that trips people up most, because it's not just 'the difference as a percentage of the original number' unless you're careful about which number is the base. The formula is: ((New Value − Old Value) / Old Value) × 100. If a product's price rose from ₹400 to ₹460, that's ((460−400)/400) × 100 = 15% increase. Note the denominator is always the original (old) value, not the new one — using the new value as the base gives a different, incorrect answer.

Reverse percentage — finding the original price from a discounted one

If an item is on sale for ₹850 after a 15% discount, what was the original price? You can't just add 15% back to ₹850 — that's the same inclusive/exclusive mistake as with GST. Instead: Original Price = Discounted Price / (1 − Discount% / 100) = 850 / 0.85 = ₹1,000.