Percentage Calculator

How to Use the Percentage Calculator

1. Pick a mode: X% of Y, X is what % of Y?, or Increase / decrease.
2. Enter the two numbers. Labels update to tell you exactly what each field means.
3. Read the live result — the big number, a plain-English description, and the formula used.
4. Copy the result with one click for messages, documents, or spreadsheets.

Features That Set This Tool Apart

• Three modes in one page — the forward, reverse, and change calculations people actually need.
• Live answers — this percentage calculator updates as you type, no button needed.
• Visible formulas — every result shows its working, so you learn the math, not just the answer.
• Increase and decrease — enter a negative percent for decreases; the difference is shown too.
• Smart formatting — thousands separators and sensible rounding for readable results.
• One-click copy — grab the full “20% of 150 = 30” statement.
• Private — all math runs in your browser.

Percentage Calculator Formulas, Explained

X% of Y: divide the percent by 100, then multiply. 20% of 150 = (20 ÷ 100) × 150 = 30. This is the tip, tax, and commission calculation.

X is what % of Y: divide X by Y, then multiply by 100. 45 is what % of 60? (45 ÷ 60) × 100 = 75%. This is the exam-score and progress calculation.

Increase/decrease by P%: multiply by (1 ± P/100). Increase 200 by 15%: 200 × 1.15 = 230. Decrease 200 by 15%: 200 × 0.85 = 170. This is the salary-hike and discount calculation. Note that increasing by 10% then decreasing by 10% does not return to the start (110 → 99) — the base changes each time.

5 Percentage Mistakes Everyone Makes

1. Adding percentages directly. A 20% rise followed by a 20% fall leaves you at 96%, not 100% — each change applies to a new base.
2. Confusing percentage points with percent. Going from 10% to 15% is a 5 percentage point rise but a 50% relative increase.
3. Forgetting the base. “50% off, then 50% off again” is 75% off total, not 100% — the second discount applies to the already-reduced price.
4. Misreading “X% more than.” “30% more than 200” is 260 (200 × 1.3), not 60.
5. Rounding too early. Round only the final answer; intermediate rounding drifts the result.

Percentages in Everyday Life

Percentages quietly govern money and marks. Shoppers meet them in discounts and sales tax; employees in salary increments and deductions; students in exam scores and grading thresholds; investors in returns and interest. Because the same symbol means different things in different contexts — a share of a whole, a rate of change, a margin — the first step is always identifying which percentage question you are asking. That is why the calculator separates the three modes: pick the question first, and the math follows.

Percentage Shortcuts for Mental Math

You do not always need a calculator. These shortcuts handle most everyday percentages in your head:

• 10%: move the decimal point one place left. 10% of 240 is 24.
• 5%: halve the 10% value. 5% of 240 is 12.
• 1%: move the decimal two places left. 1% of 240 is 2.40.
• 15%: add 10% + 5%. 15% of 240 is 24 + 12 = 36 — the classic restaurant tip.
• 20%: double the 10% value. 20% of 240 is 48.
• 25%: divide by 4. 25% of 240 is 60.
• 50%: halve it. 75%: halve, halve again, and subtract from the whole — or simply compute 100% minus 25%.

Combine building blocks for anything else: 35% is 25% + 10%, and 12% is 10% + 1% + 1%. For exact answers with awkward numbers, though, the percentage calculator above is faster and never slips a decimal place.

Reverse Percentages: Finding the Original Price

Reverse percentages answer “what was it before?” — the original price before a discount, the pre-tax amount, or last year’s salary before a raise. The formula is original = final ÷ (1 ± rate).

Example: a jacket costs Rs 1,700 after a 15% discount, so the original price was 1,700 ÷ 0.85 = Rs 2,000. Example: your salary is Rs 57,500 after a 15% raise, so last year it was 57,500 ÷ 1.15 = Rs 50,000.

The common mistake is adding the percent back: 15% of 1,700 is 255, giving 1,955 — wrong, because the 15% applied to the original, not the final price. Division undoes multiplication; addition does not. Whenever a problem gives you the “after” number, divide, do not add. The X is what % of Y mode above handles the percentage side: enter the saving and the original price to reveal the true discount percent.

Percentage Pro Tips

For mental math, find 10% first by moving the decimal point one place, then scale — 30% is just three times 10%. To reverse a percentage increase, divide by 1 plus the rate: undoing a 20% rise means dividing by 1.20, not subtracting 20%. Never confuse percentage points with percent: a rise from 10% to 15% is five percentage points but a 50% relative increase. When comparing discounts, apply them sequentially rather than adding — two 20%-off coupons equal 36% off, not 40%. Keep this calculator bookmarked for the cases where precision matters more than speed.

Percentage Calculator: Frequently Asked Questions

How do I calculate a percentage of a number?

Select the X% of Y mode, enter the percentage and the number. The calculator divides the percent by 100 and multiplies — for example, 20% of 150 is 30. The formula is shown under the result so you can verify the working.

How do I find what percent one number is of another?

Use the X is what % of Y mode. Enter the part and the whole — for example, 45 as the part and 60 as the whole gives 75%. The formula is (part ÷ whole) × 100. This is the mode to use for exam scores, completion rates, and market shares.

How do I calculate a percentage increase or decrease?

Choose the Increase / decrease mode, enter the original value and the percent change (negative for a decrease). The tool multiplies by (1 ± percent/100) and also shows the absolute difference. A 15% increase on 200 gives 230; a 15% decrease gives 170.

Why don’t two opposite percentage changes cancel out?

Because the base changes. Increasing 100 by 10% gives 110; decreasing 110 by 10% gives 99, not 100. Each percentage applies to the current value, not the original — so always chain calculations through the running total, which this calculator does automatically.

Is my data sent anywhere?

No. Every calculation runs in JavaScript inside your browser. Nothing you type is uploaded, stored, or logged, and there is no account or tracking of any kind. Your numbers stay on your device, and the calculator keeps working offline once the page has loaded.

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• Discount Calculator — sale prices, savings, and stacked discounts.
• Tip & Bill Split Calculator — tips, tax, and splitting the bill fairly.
• GPA Calculator — compute grade point averages from your courses.
• All Free Tools — browse the complete collection of free online tools — no signup needed.

Percentages stop being intimidating once you see the formula. Keep this percentage calculator handy, and the next tip, discount, or score will take five seconds flat.