How to Calculate Percentages Online for Free (2026 Guide)

Percentages are everywhere: exam marks, sale discounts, tax, tips, salary raises, battery levels. The arithmetic is simple in theory but surprisingly easy to fumble under time pressure — especially "X is what percent of Y?" and percentage-change problems. A free online percentage calculator handles all four common problem types instantly. This guide shows you how to use each mode, with worked examples you can verify by hand.

Step 1: Open the Percentage Calculator

Open our Percentage Calculator. It's free, needs no signup, and computes entirely in your browser.

Step 2: Pick the right mode

The tool has a Mode dropdown with four options — choosing the right one is the only skill involved:

• "What is X% of Y?" — find a portion of a number (discounts, tax, commission)
• "X is what % of Y?" — express one number as a share of another (marks, market share)
• "Increase X by Y%" — add a percentage (salary raise, price hike)
• "Decrease X by Y%" — subtract a percentage (sale price, depreciation)

Then enter your two numbers in the X and Y fields and click "Calculate".

Mode 1 example: What is 20% of 200?

A shop offers 20% off a 200 item. Select "What is X% of Y?", enter X = 20, Y = 200:

• Math: 20 ÷ 100 × 200 = 40
• Meaning: the discount is 40, so you'd pay 160 (for the final price, try our Discount Calculator).

Quick sanity trick: 10% of anything is just the number divided by 10 (10% of 200 = 20), so 20% is double that = 40. If the tool's answer disagrees with your mental estimate, re-check which mode you picked.

Mode 2 example: 45 is what % of 180?

You scored 45 marks out of 180. Select "X is what % of Y?", enter X = 45, Y = 180:

• Math: 45 ÷ 180 × 100 = 25%
• Meaning: you got 25% — a failing grade most places, but at least now you know exactly.

This mode is also how businesses compute things like "what share of our revenue came from product X" — just put the part in X and the whole in Y.

Mode 3 example: Increase 1,200 by 15%

Your 1,200 salary gets a 15% raise. Select "Increase X by Y%", enter X = 1200, Y = 15:

• Math: 1,200 × (1 + 15 ÷ 100) = 1,200 × 1.15 = 1,380
• Meaning: your new salary is 1,380 — a raise of 180.

Common mistake: adding 15 to 1,200 (getting 1,215) instead of adding 15 percent. The tool never makes that error.

Mode 4 example: Decrease 750 by 30%

A 750 gadget drops 30% in a clearance sale. Select "Decrease X by Y%", enter X = 750, Y = 30:

• Math: 750 × (1 − 30 ÷ 100) = 750 × 0.70 = 525
• Meaning: the sale price is 525; you save 225.

Everyday situations for each mode

• X% of Y: restaurant tax, agent commission, "20% of your daily calories"
• X is what % of Y: exam scores, project completion, budget spent vs. planned
• Increase by: pay raises, rent hikes, investment growth, inflation adjustments
• Decrease by: sale prices, depreciation, "cut sugar by 25%"

Percentage points vs. percent — don't mix them up

A subtle trap: if interest rises from 5% to 7%, that's a 2 percentage-point increase — but a 40% relative increase (2 ÷ 5). News headlines and ads exploit this confusion constantly ("50% fewer calories!" vs. "50 percentage points fewer" are very different claims). When a change sounds dramatic, check which one is meant.

Tips for error-free percentage math

• Match the mode to the question: "what percent" questions need mode 2; "how much after" questions need mode 3 or 4.
• Watch the decimal point: 0.5% of 1,000 is 5, not 500. The tool handles this, but your expectations should too.
• Verify with a rough estimate: 33% of 900 should be near 300. If the answer looks wildly off, you likely swapped X and Y.
• Chain carefully: two successive 10% discounts are NOT a 20% discount — the second 10% applies to the already-reduced price (see our Discount Calculator guide).

Frequently asked questions

Is the percentage calculator free?

Yes — free, unlimited use, no signup, runs in your browser.

How do I calculate percentage increase between two numbers?

Use mode 2 ("X is what % of Y?") with X = the difference and Y = the original. Example: price rose from 50 to 65 → X = 15, Y = 50 → 30% increase.

What if Y is zero?

Percentage of zero (or change from zero) is mathematically undefined — the tool returns 0 rather than an error. In real terms, "growth from zero" is infinite, so describe it in absolute numbers instead.

Can it handle decimals?

Yes — enter values like 12.5% or 99.99 without worry; results show up to two decimal places.

Solve it in seconds: Free Percentage Calculator — four modes, zero signup.