Percentage guides
100 guides to percentages in everyday use: shopping, pay, grades, data, business and spreadsheets. Each one works through real numbers and links to a calculator with those numbers filled in.
Good places to start
Percentage basicsHow to calculate a percentage: the three formulas you need
Every basic percentage question is one of three shapes: find the part, find the percentage, or find the whole. Here's how to tell which one you have.
Increase and decreaseHow to calculate percentage increase
Subtract the old value from the new one, divide by the old value, and multiply by 100. Worked examples with prices, rent and scores, plus a quick way to check the answer.
Discounts and shoppingHow to calculate a discount: sale price and savings
To find a sale price, multiply the original price by 1 minus the discount. Two methods, mental shortcuts for common discounts, and how to check what you'll pay.
Increase and decreasePercentage change vs percentage difference: which one to use
Use percentage change when one value is clearly the starting point, and percentage difference when neither is. The same pair of numbers worked both ways.
Percentage basicsReverse percentages: how to find the original number
To undo a percentage change, divide by the multiplier instead of subtracting the percentage. Why the obvious method fails, and how to check your answer.
SpreadsheetsHow to calculate a percentage in Excel
The basic Excel percentage formula is =part/whole, formatted as a percentage. Copy-ready formulas for percent of target, percent of a number, increases, decreases and percentage change, with a worked sheet.
All guides
Percentage basics
- How to calculate a percentage: the three formulas you need
- How to find a percentage of a number: three methods
- What percent is X of Y? Turning a part and a total into a percentage
- Reverse percentages: how to find the original number
- How to find the whole when you know a part and its percentage
- Percentages, fractions and decimals: how to convert between them
- Percentage points vs percent: what's the difference?
- Percentages over 100%: what they mean and when they make sense
- Seven common percentage mistakes and how to avoid them
- Basis points, per mille and parts per million explained
Increase and decrease
- How to calculate percentage increase
- How to calculate percentage decrease
- Percentage change vs percentage difference: which one to use
- Why a 50% loss needs a 100% gain to break even
- Successive percentage changes: why +10% then −10% isn't zero
- How to increase or decrease a number by a percentage
- How to calculate percentage change with negative numbers
- Percentage change from zero: why it's undefined and what to report
- Absolute vs relative change: comparing growth of different sizes
- Year-over-year vs month-over-month growth: how to calculate and read them
Discounts and shopping
- How to calculate a discount: sale price and savings
- How to work out the discount percentage from the original and sale price
- Stacked discounts: why 20% off plus 10% off isn't 30% off
- Percent off vs dollar off: which coupon saves more?
- Buy one, get one free and other multibuy deals as a percentage
- How to find the original price from a sale price
- Cashback vs discount: comparing percentage rewards
- Unit price comparisons: how much cheaper is the bigger pack?
- Discount first or tax first? Calculating the final price at the till
- Annual vs monthly plans: what percentage do you really save?
Personal finance
- How to calculate your savings rate
- Budget percentages: the 50/30/20 split worked through
- How to calculate a pay raise percentage
- Simple interest explained with worked examples
- Compound interest: how percentage growth builds on itself
- How inflation shrinks purchasing power: the percentage math
- Investment returns: total return and annualized return (CAGR)
- APR vs APY: what the two percentages mean
- How to calculate your debt-to-income ratio
- Portfolio allocation percentages and how to rebalance
School and grades
- How to calculate a test score percentage
- How to calculate a weighted grade
- What score do I need on my final exam?
- Percentage vs percentile: what your score report means
- How to calculate attendance percentage
- How much did my grade improve? Points vs percent
- How many questions do I need right to pass?
- How to calculate a class average and pass rate
- Percent error: the formula and how to use it in lab reports
- Percentage word problems: a method that works every time
Business and ecommerce
- How to calculate profit margin
- Markup vs margin: the difference and how to convert between them
- How to set a price for a target profit margin
- How to calculate conversion rate and compare it between periods
- Click-through rate (CTR): formula and examples
- How to calculate customer churn rate and retention rate
- How to calculate budget variance as a percentage
- Contribution margin ratio and break-even sales
- How to calculate sales commission, including tiered rates
- How to calculate market share
Statistics and data
- Row, column and total percentages in a data table
- Relative frequency and cumulative percentages
- How to average percentages correctly
- Reading poll percentages: what the margin of error means
- How charts make percentage changes look bigger than they are
- Why percentages don't always add up to 100
- Comparing groups of different sizes: percentages and rates per 1,000
- Simpson's paradox: when the overall percentage tells the opposite story
- Index numbers: setting a base of 100 to compare growth
- Relative risk vs absolute risk in health headlines
Tax, VAT and tips
- How to calculate sales tax on a purchase
- How to work out the price before sales tax from a total
- How to calculate VAT on a net price
- How to remove VAT from a VAT-inclusive price
- How to calculate a tip: 15%, 18% and 20% in your head
- How to split a bill with tax and tip
- Should you tip on the pre-tax or the after-tax amount?
- Service charges vs tips: reading the percentages on your bill
- Combined sales tax rates: state, county and city
- Effective tax rate vs marginal tax rate
Work and everyday
- How to calculate project completion percentage
- How to measure a productivity change as a percentage
- Utilization rate: how to calculate it for people and equipment
- How to calculate a survey response rate
- How to calculate progress toward a goal
- Quick percentage estimates without a calculator
- How to work out time as a percentage of a day or week
- How to scale a recipe up or down by a percentage
- Shrinkflation: how to calculate the hidden price increase
- Overtime pay: time and a half and other pay rate percentages
Spreadsheets
- How to calculate a percentage in Excel
- Percentage change formula in Excel and Google Sheets
- How to calculate percentages in Google Sheets
- Why Excel shows 2500% instead of 25%, and other format problems
- How to add or subtract a percentage in a spreadsheet
- Discount and sale price formulas for spreadsheets
- Percent of total in a spreadsheet with absolute references
- VAT and sales tax formulas in spreadsheets
- Percentage charts in spreadsheets: pie, stacked bar or something else
- Common spreadsheet percentage errors and how to fix them
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