Percentages, explained (in plain English)

A percentage is a way to describe a part of something out of 100. If you see 25%, that literally means “25 out of 100”. Percentages are everywhere because they make comparisons simple: discounts, interest rates, grade scores, growth rates, tax, tips, battery levels, and even how much of your budget went to rent.

This Percentage Calculator supports the most common percentage questions people actually ask: “What is X% of Y?”, “X is what percent of Y?”, “What’s the percent change from old to new?”, and “Increase/decrease a number by X%.” Each one uses a slightly different formula — and choosing the right one is the difference between “that looks right” and “why is this number so weird?”

This is the classic “percentage of a number” problem. Convert the percent to a decimal and multiply:

• Result = (P ÷ 100) × Y

Example: What is 15% of 200? (15 ÷ 100) × 200 = 0.15 × 200 = 30. This is used for tips, discounts, commissions, and “I want to save 20% of my salary.”

This asks for the percentage relationship between two values: the “part” (X) and the “whole” (Y). Divide, then multiply by 100:

• Percent = (X ÷ Y) × 100

Example: 50 is what percent of 200? (50 ÷ 200) × 100 = 0.25 × 100 = 25%. If Y is 0, this is undefined (you can’t divide by zero), and the calculator will warn you.

Percent change tells you how much something increased or decreased relative to where it started. It’s one of the most viral, screenshot-friendly numbers in finance and social posts: “My rent went up 12%”, “Traffic increased 30%”, “Stock dropped 8%”.

• Percent change = ((New − Old) ÷ Old) × 100

Example: Old = 80, New = 100 → ((100−80)÷80)×100 = (20÷80)×100 = 25%. If Old is 0, percent change is not defined in the usual way (anything over zero would be an infinite increase), so the calculator will display a helpful message instead of a misleading number.

If you’re raising a value by P percent, you’re adding P% of it back onto itself:

• New value = Base × (1 + P ÷ 100)

Example: Increase 120 by 10% → 120 × (1 + 0.10) = 120 × 1.10 = 132. This is used for raises, price increases, and forecasting.

Decreasing is the opposite: you keep (100 − P)% of the original:

• New value = Base × (1 − P ÷ 100)

Example: Decrease 250 by 20% → 250 × 0.80 = 200. Used for discounts and markdowns.

People mix this up constantly. If conversion rate goes from 2% to 3%, that’s a 1 percentage point increase, but it’s a 50% increase relative to the starting value (because (3−2)/2 = 0.5). This calculator’s “Percent change” mode gives you the relative change; percentage points are simply New% − Old%.

What this calculator does behind the scenes

The calculator is built for speed and clarity: you pick a question type, enter the numbers, and it instantly applies the matching formula. To keep results “shareable”, the output includes:

• A clean main result (number or percent).
• A short human explanation (“X is Y% of Z”).
• A visual meter when the output is a percentage, so screenshots look good on social.
• Optional save so you can compare multiple scenarios (stored locally in your browser).

All calculations run entirely in your browser. Nothing is uploaded. It’s fast, private, and works offline once loaded.

For most real-world uses, a few decimals are enough. This tool formats results nicely: whole numbers stay clean, while decimals are trimmed to a sensible number of places. If you need strict rounding rules (significant figures, scientific notation, etc.), you can jump to the related calculators below.

• Using “percent of” when you need “percent change” (discount vs growth).
• Dividing by the wrong base (change should be divided by Old, not New).
• Confusing percent vs percentage points for rates and metrics.
• Forgetting to convert percent to decimal when multiplying.

Real-life percentage examples you can copy

A jacket is $80 and it’s 25% off. What’s the discount amount? Use P% of Y: 25% of 80 = 20. Final price = 80 − 20 = 60.

Dinner is $46. Want to tip 18%? 18% of 46 = 8.28. Total = 54.28. (If you like quick tipping, also check the Tip Calculator in the Popular Tools section.)

You got 42 points out of 50. What percent is that? Use X is what percent of Y: (42 ÷ 50) × 100 = 84%.

You make $70,000 and get a 6% raise. Increase by 6%: 70,000 × 1.06 = 74,200. The raise amount is 4,200.

Your favorite subscription went from $9.99 to $12.99. Percent change: ((12.99 − 9.99) ÷ 9.99) × 100 ≈ 30.03% increase.

You ran a mile in 10:00 and now you run it in 8:30. If you treat time as a number (minutes), Old = 10, New = 8.5 → percent change = ((8.5 − 10) ÷ 10) × 100 = −15%. Negative means improvement (less time).

Engagement rate from 4% to 6% is +2 percentage points, but it’s a 50% increase. Use percent change with Old = 4 and New = 6 → ((6−4)/4)×100 = 50%.

Frequently Asked Questions

• What’s the difference between “X% of Y” and “X is what percent of Y”?

  “X% of Y” outputs a number (a portion of Y). “X is what percent of Y” outputs a percentage showing how big X is compared with Y.

• Why is percent change divided by the old value?

  Percent change measures how big the change is relative to where you started. Dividing by Old makes it a “starting-point” comparison. Dividing by New answers a different question.

• What if the old value is 0?

  Standard percent change isn’t defined when Old = 0 because you’d divide by zero. In practice, people describe this as “from 0 to X” rather than a finite percentage.

• Can percentage results be over 100%?

  Yes. If X is bigger than Y, then (X ÷ Y) × 100 is over 100%. Example: 150 is 150% of 100. The meter will cap its display at 100 for visualization, but the numeric result will still be correct.

• Is a negative percent change bad?

  Not always. Negative simply means “decrease.” For costs, a decrease might be great. For revenue, it might be bad. Context matters.

• How many decimals should I use?

  For money, 2 decimals is common. For growth metrics, 1–2 decimals is usually enough. For scientific work, use significant figures instead.

• Does this calculator store my numbers?

  Calculations run in your browser. If you use “Save Result”, it stores a small history in local storage on this device only.