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Guides
Short, practical explanations to help you choose the right inputs and understand your results.
Business
Understand the difference between margin and markup with simple examples.
Read guide →Money
Learn how principal, rate, time, and compounding frequency affect growth.
Read guide →Developer
A practical guide to valid JSON syntax and readable formatting.
Read guide →Money
Three everyday percentage calculations explained step by step, with worked examples you can check.
Read guide →Money
Understand the amortisation formula behind monthly loan and mortgage payments, and what changes the total cost.
Read guide →Money
See how the two methods differ, with side-by-side numbers and when each one is used.
Read guide →Business
Find the number of sales you need to cover your costs, and how to use the result to make better pricing decisions.
Read guide →Business
How consumption taxes work, how to add or remove them from a price, and why rates differ by country.
Read guide →Freelancer
Work backwards from your income goal to a rate that covers billable hours, expenses and tax.
Read guide →Developer
A clear explanation of Base64 encoding, what it is for, and why it is not encryption.
Read guide →Developer
What a Unix timestamp is, how to read one, and the seconds-versus-milliseconds trap.
Read guide →Everyday
Why converting a meeting time is trickier than adding a fixed number of hours.
Read guide →Everyday
The most useful conversions between metric and imperial units, and how to avoid common mix-ups.
Read guide →Money
Work out sale prices, stacked discounts and the original price from a discounted one.
Read guide →Money
Return on investment explained: the formula, how to compare investments fairly and where ROI falls short.
Read guide →Business
What comes off your pay, how to estimate take-home pay and how to compare job offers.
Read guide →Freelancer
A step-by-step method for quoting fixed-price work without underpricing yourself.
Read guide →Everyday
How body mass index is calculated, what the categories mean and why it is only a screening tool.
Read guide →Everyday
Why counting days, months and years between two dates is trickier than it looks.
Read guide →Developer
Why URLs need percent-encoding, which characters are affected and how to encode and decode safely.
Read guide →Developer
How UUIDs work, what version 4 means and where they are a good choice for identifiers.
Read guide →Everyday
Three ways to describe the middle of a data set, when each one is best and how outliers change them.
Read guide →Everyday
Calculate tips, add them to the bill and share the total fairly between friends.
Read guide →Money
Step-by-step formulas for percentage change, with examples for prices, salaries and growth, plus how to apply a percentage rise or fall.
Read guide →Business
Calculate gross, operating and net profit margin step by step, with a worked example and tips for improving your margin.
Read guide →Money
A practical way to estimate an affordable home price from your income, debts and down payment using common lending guidelines.
Read guide →Business
Turn a yearly salary into an hourly rate, or an hourly wage into a yearly salary, with the standard hours and your own working weeks.
Read guide →Everyday
The formulas for converting between Celsius, Fahrenheit and Kelvin, with reference points and quick mental shortcuts.
Read guide →Everyday
Estimate reading and speaking time from a word count, and how to use it for blog posts, speeches and presentations.
Read guide →Everyday
Work out how much fuel a trip needs and what it will cost, in kilometres and litres or miles and gallons.
Read guide →Everyday
Work out your pace per kilometre or mile, predict race finish times and convert between kilometre and mile pace.
Read guide →Business
Understand the difference between gross and net profit, how each is calculated and what they tell you about a business.
Read guide →Developer
What makes a password strong, how entropy works, and practical rules for passwords, passphrases and password managers.
Read guide →Money
Understand equated monthly instalments, the EMI formula, how tenure changes total interest and the difference between flat and reducing-balance rates.
Read guide →Developer
When to use camelCase, PascalCase, snake_case, kebab-case and CONSTANT_CASE in code, files and URLs.
Read guide →