Guides

How to Calculate a Percentage

Percentages show up everywhere — discounts, grades, statistics, tips. This guide covers the three most common percentage questions and the formula behind each.

How to Calculate Percentage Increase

Percentage increase measures how much a value has grown, expressed as a fraction of its starting point — useful for salaries, prices, and performance metrics.

How to Calculate Percentage Decrease

Percentage decrease measures how much a value has dropped, expressed as a fraction of its starting point — common for price drops, weight loss, or performance decline.

How to Calculate a Discount

Working out a sale price is simple once you know the formula — and knowing how stacked discounts actually combine can save you from overestimating your savings.

What Is BMI and How to Calculate It

Body Mass Index (BMI) is a simple ratio of weight to height used as a quick screening tool for weight categories — it's not a diagnosis, but a starting point.

Simple vs Compound Interest: What's the Difference?

Simple and compound interest sound similar but produce very different results over time — the difference is whether interest earns interest of its own.

How to Calculate Your Exact Age

Calculating age sounds trivial — subtract the birth year from the current year — but that only works if the birthday has already happened this year.

What Is JSON and How to Format It

JSON (JavaScript Object Notation) is a lightweight, text-based format for structuring data — used everywhere from API responses to config files.

What Is Base64 Encoding?

Base64 is a way of representing binary data as plain ASCII text — useful whenever a system can only safely handle text, not raw bytes.

Why and How to URL Encode Text

URLs can only safely contain a limited set of characters — URL encoding (percent-encoding) converts everything else into a safe, unambiguous form.

What Is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit value used to identify something — a database row, a session, a file — without needing a central authority to hand out unique numbers.

How to Write a Good Meta Title

Your meta title is the first thing people see in search results — it needs to fit Google's display limit and give someone a real reason to click.

How to Write a Good Meta Description

A meta description doesn't directly affect rankings, but it's your pitch to searchers — a good one earns clicks; a bad one (or none at all) leaves them guessing.

How to Create a Good URL Slug

A URL slug is the readable part of a web address that identifies a specific page — a clean slug helps both users and search engines understand what a page is about at a glance.

Celsius to Fahrenheit: How the Conversion Works

Celsius and Fahrenheit don't share a zero point, which is why converting between them needs both a multiplication and an offset — not just a simple ratio like most unit conversions.

Metric vs Imperial: Common Length Conversions

Metric and imperial length units coexist in everyday life — recipes, DIY projects, road signs, and international specs often mix the two, so knowing the key conversions helps.

How to Calculate GPA

GPA (Grade Point Average) summarizes your academic performance as a single number by weighting each course's grade by how many credit hours it's worth.

Gross vs Net Salary: What's the Difference?

Gross and net salary are often confused, but the gap between them — taxes and social contributions — is usually the single biggest factor in what actually lands in your bank account.

Comment calculer l'indemnité de licenciement

L'indemnité légale de licenciement est un minimum garanti par le Code du travail — voici comment elle se calcule, étape par étape.

Comment calculer son impôt sur le revenu

L'impôt sur le revenu en France utilise un barème progressif par tranches, ajusté par le quotient familial — voici comment ça fonctionne concrètement.

How to Find the GCD and LCM of Two Numbers

GCD and LCM are two related ways of describing how two numbers relate to each other — one finds their largest shared factor, the other their smallest shared multiple.

How to Check If a Number Is Prime

A prime number has exactly two divisors — 1 and itself. Here's the fastest manual method for checking, and why it works.

What Is a Hash and How Does It Work?

A hash function takes any input and produces a fixed-length string of characters — the same input always produces the same hash, but you can't reverse it back to the original.

HEX vs RGB Color Codes Explained

HEX and RGB are two ways of writing down the exact same color information — one is more compact, the other more human-readable for each color channel.

How Regular Expressions Work (A Beginner's Guide)

A regular expression (regex) is a pattern that describes text to search for — instead of matching an exact string, it matches a shape of text.

What Is a Leap Year and Why Does It Exist?

A leap year adds an extra day (February 29) to keep our calendar synchronized with Earth's actual trip around the sun.

JPG vs PNG vs WebP: Which Should You Use?

The three most common web image formats each make different trade-offs between file size, quality, and features — picking the right one matters for both page speed and image quality.

How to Compress an Image Without Losing Much Quality

Most of a large image's file size can be trimmed with almost no visible quality loss, if you approach it in the right order.

What Is a Favicon and How Do You Create One?

A favicon is the small icon shown in a browser tab, bookmark list, and (on mobile) home screen shortcut for a website.

How to Check Keyword Density (and Why It Matters Less Than You Think)

Keyword density measures how often a word or phrase appears relative to a page's total word count — once treated as an SEO secret, it's now a minor signal at best.