3-in-1 percentage calculator
Built & maintained by Pappu Venkata Subbi Reddy, founder of Clacify · Updated August 2026
Percentage Calculator solves the three percentage problems people actually run into, not just one. Mode 1 answers "what is X% of Y?" — for discounts, tips, commissions, or GST amounts. Mode 2 answers "X is what % of Y?" — for turning marks or a proportion into a percentage, like 45 out of 60. Mode 3 answers "what's the percentage change from A to B?" — for salary hikes, price increases, or year-on-year comparisons, and correctly reports a decrease as a negative number rather than hiding the direction of the change. Most percentage confusion comes from picking the wrong one of these three formulas, not from the arithmetic itself, so the calculator is built around choosing the right mode rather than just crunching numbers. Everything runs instantly in your browser as you type.
Mode 1 (X% of Y) multiplies Y by X and divides by 100: Y × X ÷ 100. Mode 2 (X is what % of Y) divides X by Y and multiplies by 100: (X ÷ Y) × 100. Mode 3 (percentage change from A to B) subtracts A from B, divides by A, and multiplies by 100: [(B − A) ÷ A] × 100 — dividing by the original value A, not the new value B, which is the single most common source of manual calculation errors in this space. All three run as pure client-side arithmetic on every keystroke, so there's no submit step and no rounding is applied beyond what you see on screen.
| GST rate | GST amount | Total with GST |
|---|---|---|
| 5% | ₹50 | ₹1,050 |
| 12% | ₹120 | ₹1,120 |
| 18% | ₹180 | ₹1,180 |
| 28% | ₹280 | ₹1,280 |
18% is the most common GST slab in India for restaurants, services, and most goods. Use Mode 1 above (₹1,000 × 18 ÷ 100) to check any amount instantly.
If you know a percentage and a total and want the resulting amount — a 20% discount on a ₹2,000 jacket, or 18% GST on a ₹500 bill — that's Mode 1. If you know two amounts and want to express one as a percentage of the other — you scored 45 out of 60 and want the percentage, or ₹15,000 rent is what percentage of a ₹60,000 salary — that's Mode 2. If you're comparing an old value to a new one and want the percentage change between them — your salary went from ₹40,000 to ₹50,000, or a product's price rose from ₹800 to ₹950 — that's Mode 3. Picking the wrong mode is the most common reason people get a percentage calculation "wrong" even though their arithmetic is fine.
Old salary ₹40,000, new salary ₹50,000. The percentage change formula divides by the OLD value: [(50,000 − 40,000) ÷ 40,000] × 100 = (10,000 ÷ 40,000) × 100 = 25%. A very common mistake is dividing by the new value instead — (10,000 ÷ 50,000) × 100 = 20% — which understates the actual hike. The same logic applies in reverse for a pay cut: going from ₹50,000 back down to ₹40,000 is a −20% change [(40,000 − 50,000) ÷ 50,000 × 100], not −25%, because the base value being divided by has changed. Percentage increases and decreases are not symmetric, which is exactly why this calculator keeps the sign and always divides by the starting value.
If interest rates move from 5% to 7%, that's a 2 percentage point increase, but a 40% relative increase [(7−5)÷5 × 100]. News reports and financial statements often use these two phrases interchangeably when they mean very different things, and mixing them up leads to real misunderstandings about how big a change actually is — a 2 percentage point rise in GST sounds small; a 40% jump in the tax amount you actually pay sounds much bigger, and both descriptions are describing the same change. When the numbers involved are themselves already percentages (interest rates, tax rates, exam pass rates), it's worth being explicit about which one you mean.
For "what is X% of Y": multiply Y by X and divide by 100. Example: 18% of ₹500 = 500 × 18 ÷ 100 = ₹90. For "X is what % of Y": divide X by Y and multiply by 100. Example: 45 out of 60 marks = (45 ÷ 60) × 100 = 75%. For percentage change: [(New − Old) ÷ Old] × 100.
Percentage = (Marks Obtained ÷ Total Marks) × 100. For example, if you scored 425 out of 500 in board exams, your percentage is (425 ÷ 500) × 100 = 85%.