Percentage Calculator – 5 Modes: Of, Change, Difference

📊 ➜ ％

Percentage Calculator

Five percentage tools in one — percent of a number, what percent X is of Y, percentage increase/decrease, percentage difference, and add or subtract a percent. Live answers, formulas shown, works offline. Free and private.

✓ 5 Modes · ✓ Formulas Shown · ✓ Instant & Offline

🔧 JS ⏳ · Input — · Result — · Engine ⏳

% of =

—

Formula: X% of Y = X ÷ 100 × Y   e.g. 15% of 80 = 15 ÷ 100 × 80 = 12

💡 Discounts, tips, tax, portions — the everyday percentage.

is what % of =

—

Formula: X ÷ Y × 100   e.g. 12 is what % of 80 = 12 ÷ 80 × 100 = 15%

💡 Test scores, market share, portion of budget, goal progress.

→ =

—

Formula: (New − Old) ÷ Old × 100   e.g. 80 → 100 = (100−80) ÷ 80 × 100 = +25%

💡 Price moves, sales growth, weight change, KPI tracking. Negative = decrease.

vs =

—

Formula: |A − B| ÷ ((A + B) ÷ 2) × 100   e.g. 40 vs 50 = 10 ÷ 45 × 100 = 22.22%

💡 Symmetric comparison when neither value is the "original" — measurements, quotes, experiments.

➕ add ➖ subtract %

—

Formula: Value × (1 ± X÷100)   e.g. add 25% to 200 = 200 × 1.25 = 250

💡 Markup, tax added, discount applied, salary raises, price cuts.

How to Calculate Percentages — All the Formulas

Every percentage question is one of five shapes. Each formula below matches a tab in the calculator above — results appear live, with the math visible:

1️⃣ Percent of a number

X% of Y = X ÷ 100 × Y

"15% of 80" → 12. Used for discounts, tips, taxes and portions.

2️⃣ One number as a percent of another

X ÷ Y × 100

"12 is what percent of 80?" → 15%. Used for scores, shares and progress.

3️⃣ Percentage change

(New − Old) ÷ Old × 100

Directional — a negative result is a decrease. Used for prices, growth and KPIs.

4️⃣ Percentage difference

|A − B| ÷ ((A + B) ÷ 2) × 100

Symmetric — no "original" needed, so A-vs-B and B-vs-A give the same answer.

Why Use This Online Percentage Calculator?

5️⃣

Every % Question

Five modes cover percent-of, what-percent, change, difference and add/subtract — no second tool needed.

📖

Formulas On Screen

Each mode shows its formula with a worked example — you learn the math while getting the answer.

⚡

Live Results

No calculate buttons — answers update on every keystroke with full precision.

🔒

100% Private

Your numbers never leave the browser. Nothing sent, stored, or logged.

📶

Offline & Free

Pure JavaScript — unlimited use, no account, works without internet.

📱

Mobile Friendly

Large inputs and touch-friendly tabs — perfect for quick math at the store.

Popular Use Cases

• 🏷️ Sale math — "30% off $79.99" via X% of Y, or the Add/Subtract mode directly
• 📈 Business KPIs — month-over-month percentage change on revenue or traffic
• 🎓 Test scores — "42 out of 50 is what percent?"
• 🧾 Tax and tip — add 8.5% or 18% to any base amount
• 🔬 Lab comparisons — symmetric difference between two measurements
• 🏋️ Fitness progress — body-weight change over time in clean percentages

Pro Tips for Percentage Math

• Change vs difference — pick deliberately: % change compares new against a defined original (directional). % difference is symmetric between two equals. Mixing them up is the most common percentage mistake.
• The reversal trap: 80 → 100 is +25% up, but 100 → 80 is −20% down. Same gap, different bases. Never assume a reverse move undoes the same percentage.
• Percentages of percentages: a 10% discount then another 10% off is 19% total off, not 20% — the second applies to the reduced price. Use Add/Subtract mode twice to see it.
• Percent vs percentage points: going from 4% to 5% interest is a 1 percentage-point rise, but a 25% increase. News headlines confuse these constantly.
• X% of Y flips: 8% of 50 equals 50% of 8 — one trick for fast mental math when one number is easy.

Frequently Asked Questions

Identify which of the five questions you're asking, then use the matching tab: percent of a number (X ÷ 100 × Y), what percent (X ÷ Y × 100), percentage change ((new − old) ÷ old × 100), difference, or add/subtract. Each tab above shows its formula and updates live.

Use the % Change tab: (new value − old value) ÷ old value × 100. Going from 80 to 100 is (100−80)÷80×100 = +25%. A negative result means a decrease. This is the formula behind every "percentage increase calculator".

Percentage change is directional — it needs an original value, so 80→100 is +25% while 100→80 is −20%. Percentage difference is symmetric: it divides by the average of both values, so comparing 40 and 50 gives 22.22% whichever way round you enter them.

Use the Add/Subtract tab: value × (1 ± X/100). Adding 25% to 200 gives 250; subtracting 25% gives 150. This covers markups, taxes, discounts and raises in one place.

Two ways: "X% of Y" gives the discount amount (subtract it yourself), or "Add/Subtract %" with subtract selected gives the final price directly — for example, 79.99 minus 30% = 55.99.

The second discount applies to the already-reduced price. 100 with 10% off becomes 90; another 10% off that is 81 — a total of 19% off, not 20%. Stack discounts in the Add/Subtract tab to see it live.

No. All math runs in your browser with JavaScript. Your numbers are never sent, stored, or seen by anyone, and clearing the page wipes everything.

They're specialized percentage tools: our Tip Calculator handles tipping plus bill splitting, and the GPA Calculator converts grades via weighted averages. This page is the general-purpose percentage engine behind those use cases.