Blog

Percentages are everywhere — from sales tax and discounts to salary negotiations and mortgage rates. Yet most people were taught the formula once and have half-forgotten it. This blog is here to fix that.

Each guide answers a specific real-world question: How do I remove VAT from a price? What makes a discount genuinely good? Why do politicians and journalists use “percentage points” differently from “percent”? We explain the concept, show the formula, walk through worked examples, and link to a free calculator so you can apply it immediately.

All articles are written and reviewed by the Percentify team. If you have a topic you’d like us to cover, get in touch.

Understanding percentages

• 5 Percentage Mistakes Almost Everyone Makes
  Adding two discounts together, reversing a raise incorrectly, confusing margin with markup — avoid these surprisingly common errors.
• Percentage vs Percentage Points
  The difference between a percentage change and a percentage point change — and why it matters.
• How the Media Gets Percentages Wrong
  Cherry-picked base years, small sample sizes, confusing percent with percentage points — six patterns to watch for in news headlines.
• Percentage Increase Explained
  What percentage increase means, the formula, worked examples, and the difference between increase and percentage points.

Practical guides

• Why 20% + 10% Off Is Not 30% Off
  Two successive discounts multiply, they don’t add. Here’s the exact maths and why retailers love advertising stacked discounts.
• Mental Math for Percentages
  Practical techniques — the 1% building block, the symmetry trick, splitting awkward percentages — to calculate any % without a calculator.
• Salary Raise Percentage – What to Ask For
  How to calculate the real value of a raise, what is a “good” percentage increase, and how to negotiate effectively.
• What is a Good Discount Percentage?
  How retailers set discounts, what makes a deal genuinely good, and how to calculate your real saving.
• How to Calculate VAT
  Add VAT to a price, remove it, or find the VAT amount for any rate. Includes UK 20%, EU rates, and worked examples.
• How to Calculate a Tip
  Find the tip amount for any bill. Includes common tip percentages, mental shortcuts, and how to split the bill.
• What is 20% of a Number?
  How to find 20% of any number instantly — with a formula, examples, and a free calculator.
• Percentage Formula in Excel
  How to calculate percentages in Excel. Covers percentage of a number, percentage change, and formatting tips.
• Percentage vs Percentage Points
  The difference between a percentage change and a percentage point change — and why it matters.
• How to Calculate Percentage Error
  The formula for percentage error, worked examples, and common mistakes. Used in science, engineering, and quality control.
• How to Calculate a Pay Rise as a Percentage
  The formula and worked examples to find your pay rise percentage, compare it to inflation, and know what to ask for in a negotiation.

Free calculators

• Percentage Calculator — find X% of Y, or what percent X is of Y
• Compound Percentage Calculator — find the true effect of stacked discounts or raises
• Margin vs Markup Calculator — calculate both from cost and selling price
• Grade Calculator — find out what you need on your remaining tests
• Percentage Change Calculator
• Discount Calculator
• Tip Calculator
• VAT Calculator
• Fraction to Percentage