The knowledge side of the instrument
Learn About Percentages
Clear, step-by-step guides with formulas and real examples — every figure drawn with the same 100% reference field the calculator uses.
Percentage Academy
A structured path from the basics to applied percentage work. Follow it in order, or jump to the level you need.
Level 1 — Foundations
What a percentage is and how the core formula works.
Level 2 — Change and comparison
Increases, decreases and how to compare two numbers correctly.
- How to Calculate Percentage Increase: Formula, Steps and Examples
- How to Calculate Percentage Decrease (With Examples)
- Percentage Difference vs Percentage Change: When to Use Each
- Percentage Word Problems: A Method That Always Works
- Percentage Change Over Multiple Periods: Chaining, CAGR and Averages
- Reverse Percentage: Find the Original Price Before a Discount
- How to Calculate a Grade Percentage (and Weighted Averages)
- How to Calculate Percentage: The Complete Guide
Level 3 — Applied percentages
Percentages at work: pricing, profit and spreadsheets.
- 50 Real-World Percentage Examples (With Answers)
- How to Work Out Percentages in Your Head: 9 Fast Tricks
- Discount Percentages Explained: Sales, Stacking and Fake Deals
- How to Calculate a Tip: 15%, 18% and 20% in Your Head
- Margin vs Markup: The Difference That Costs Businesses Money
- How to Calculate Percentages in Excel and Google Sheets
- Percentages in Finance: APR, Yield, Returns and Real Rates
- Percentages in Tax and Salary: Raises, Brackets and Take-Home Pay
- Percentile vs Percentage: What the Difference Really Means
- What Is Compound Interest? The Force That Builds Wealth While You Sleep
Printable field card: all 12 formulas, the shares worth memorising and mental math shortcuts on one plate. Open the cheat sheet →
How to Calculate Percentage: The Complete Guide
Every percentage formula in one guide: percentage of a number, increase, decrease, difference, reverse, discount, VAT and markup, with worked examples.
The Percentage Formula: Every Version Explained
Every percentage formula on one page: percentage of a number, increase, decrease, reverse, difference, markup and VAT, with worked examples.
Percentage Difference vs Percentage Change: When to Use Each
Percentage difference and percentage change look alike and give different answers. Learn which to use, the exact formulas, and when each is the honest choice.
Percent vs Percentage vs Percentage Points: The Full Distinction
"Percent" and "percentage" are often interchangeable, but percentage points are different — and mixing them up can turn a 2-point rise into a 50% headline. Here's the clear rule.
50 Real-World Percentage Examples (With Answers)
Fifty worked percentage problems from shopping, salary, tax, tips, exams, cooking and investing — each with the exact working and a calculator link to verify.
How to Work Out Percentages in Your Head: 9 Fast Tricks
Nine mental-math shortcuts for percentages — the 10% anchor, the reversal trick, 1% building blocks and tipping rules — with practice problems and answers.
Discount Percentages Explained: Sales, Stacking and Fake Deals
Calculate any discount in one step: 30% off 80 = 56. Why stacked discounts never add up, and how to recover the original price.
Percentage Word Problems: A Method That Always Works
A four-step method for turning any percentage word problem into an equation, plus 12 graded problems with step-by-step solutions.
Percentages in Finance: APR, Yield, Returns and Real Rates
The percentages behind money: APR vs APY, nominal vs real returns, basis points, CAGR and drawdown maths, with worked numbers.
Percentage Change Over Multiple Periods: Chaining, CAGR and Averages
Why you cannot add percentage changes across years, how to chain them correctly, and how to turn a multi-year change into an average annual rate (CAGR).
Percentages in Tax and Salary: Raises, Brackets and Take-Home Pay
How to calculate a pay raise, understand marginal versus effective tax rates, work out take-home pay and check a VAT-inclusive invoice — with worked examples.
Reverse Percentage: Find the Original Price Before a Discount
Work backwards from a final amount to the original: 120 after +20% started at 100. Divide, never subtract — formulas and examples.
How to Calculate a Tip: 15%, 18% and 20% in Your Head
Fast mental methods for tipping, how to split a bill fairly, whether to tip on tax, and how service charges change the maths. With a full tip table.
Percentile vs Percentage: What the Difference Really Means
A percentage measures how much; a percentile measures how you rank. The difference, with test scores and salary bands.
How to Calculate a Grade Percentage (and Weighted Averages)
Turn marks into percentages, combine weighted coursework and exams, and work out the score you need on the final to hit your target grade.
How to Calculate Percentage Increase: Formula, Steps and Examples
Percentage increase = ((New − Old) ÷ Old) × 100. Example: 50 to 65 is a 30% increase. Formula, three steps and worked examples.
How to Calculate Percentage Decrease (With Examples)
Learn the percentage decrease formula with clear examples. Calculate discounts, price drops, weight loss percentages, depreciation, and more.
What Is a Percentage? Simple Explanation With Examples
Understand what percentages are, how they work, and why they matter. A beginner-friendly guide with clear examples, conversions, and everyday applications.
Margin vs Markup: The Difference That Costs Businesses Money
Markup is on cost, margin on selling price: a 50% markup is a 33.33% margin. Formulas, conversion table and worked examples.
How to Calculate Percentages in Excel and Google Sheets
Percentage formulas for spreadsheets: share of a total, percent change, reverse percentages, and the formatting trap that multiplies by 100.
What Is Compound Interest? The Force That Builds Wealth While You Sleep
Compound interest turns small, steady deposits into serious wealth over time. See real examples showing exactly how much your money can grow.
How to Calculate Compound Interest (Step-by-Step)
Learn the compound interest formula with real examples. Follow our step-by-step guide to calculate exactly how much your money grows over time.
Compound vs Simple Interest — Full Comparison With Real Numbers
See exactly how compound and simple interest differ with side-by-side dollar comparisons. Real scenarios show why the difference matters for your money.
How Interest Works: The Beginner's Guide With Real Numbers
Interest either grows your savings or inflates your debt. Understand APR, APY, and compounding with clear examples so you always know which side you're on.
Interest Calculator Explained: How to Use It Correctly
Learn how to use an interest calculator to get accurate results. Understand every input field, avoid common mistakes, and make better financial decisions.
How Much Interest Can You Earn with $10,000?
From savings accounts to index funds — see exactly how much $10,000 earns you per year and over time in every common option.
How Much Money Do You Need to Earn $1,000/Month in Interest?
Find out exactly how much capital you need to generate $1,000 per month in interest income — with real numbers for savings accounts, bonds, and investments.
How Fast Can You Double Your Money?
From savings accounts to stocks — see exactly how long it takes to double your money at every return rate using the Rule of 72.
Can You Live Off Interest Alone?
How much money do you actually need to never work again? We break down the exact numbers for different lifestyles.
7 Proven Ways to Grow Your Savings Faster in 2026
Stop letting your money sit idle. These seven actionable strategies can add thousands to your savings each year — with real numbers to prove it.
What Happens If You Save $500/Month for 10 Years?
We ran the real numbers. See exactly how much $500/month becomes in a savings account vs. invested — and why starting now matters.
How Much Should I Save Each Month to Reach $100,000?
Find out exactly how much you need to save monthly to hit $100K — with real scenarios at different interest rates, timelines, and starting amounts.
Is It Better to Save or Invest Right Now?
A real-numbers comparison of saving vs investing in today's economy. See exactly when each strategy wins — and when it doesn't.
$100 vs $1,000 Investment: What's the Real Difference?
Does investing $100/month really make a difference? We compare it head-to-head with $1,000/month over 20 years.
How Much Do You Lose by Not Investing?
Every year you wait costs you real money. See the exact dollar amount you're leaving on the table — with a real case study.
What Happens If You Start Investing at 20 vs 30 vs 40?
See the exact dollar difference between starting to invest at 20, 30, and 40. Real numbers show why every decade of delay costs you hundreds of thousands.
How to Invest Small Amounts: Turn $50/Month Into Real Wealth
You don't need thousands to start investing. See exactly how $25, $50, or $100 per month grows over 10, 20, and 30 years — with real projections.