Guides

Short, practical explanations of the numbers and file formats behind everyday tasks, each with a free tool to try it yourself.

4 min read How to merge PDF files on Windows, Mac, iPhone and Android The quickest ways to combine PDFs into one file on every device, without installing anything or uploading private documents.
5 min read How to reduce PDF file size for email and upload forms Why some PDFs are huge, which ones can be shrunk, and how to get under common size limits without making them unreadable.
5 min read How to pay off credit card debt faster Why minimum payments keep you in debt for years, and six practical steps that cut the time and the interest you pay.
5 min read Debt snowball vs. debt avalanche: which pays off debt faster? How the two most popular debt payoff methods work, a worked comparison, and how to choose between them.
6 min read How much should I save for retirement? Simple rules of thumb by age, the 4% rule, and how to turn a vague goal into a monthly savings number.
5 min read What inflation does to your savings, and how to protect them How inflation quietly reduces what your money can buy, with examples, and the main ways people keep up with it.
4 min read How to add or remove VAT and sales tax (and the common mistake) The two formulas you need for prices with and without tax, worked examples, and why subtracting the percentage gives the wrong answer.
4 min read How to make a QR code for your Wi-Fi Let guests join your Wi-Fi by scanning a code instead of typing the password. Here's how to create, test and print one.
5 min read How to create a strong password you can actually remember What makes a password hard to crack, why passphrases work so well, and simple habits that keep your accounts safe.
5 min read What is BMI, and what does your number really mean? How body mass index is calculated, what the categories mean, and the situations where BMI is misleading.
5 min read How to convert HEIC photos to JPG on iPhone, Windows and Mac Why your iPhone saves photos as HEIC, how to open them anywhere, and four ways to convert them to JPG, including one that doesn't upload your photos.
6 min read How much house can I afford? The 28/36 rule explained Lenders use two simple ratios to decide how big a mortgage you can get. Here's how they work, with worked examples and the costs people forget.
5 min read How to compress images without losing quality Practical settings for shrinking photos for email, websites and upload forms, and the three changes that save the most space.
6 min read Compound interest explained, with examples What compound interest is, why starting early matters more than investing more, and how to estimate growth in your head with the rule of 72.
4 min read How to calculate percentages in your head Five mental shortcuts for tips, discounts and percentage changes, so you can work out most percentages without a calculator.