Guides

Short, accurate explainers for the concepts behind our tools — so you understand the result, not just read it. Each guide links to the free calculator or converter that does the work for you.

• APR vs APY: Understanding the Difference Between Interest Rates

  Learn the difference between APR and APY, how compound interest makes APY higher, and where each applies. Includes formulas and real-world examples.

• Simple vs Compound Interest: Formulas, Comparison, and Real-World Applications

  The difference between simple and compound interest — with formulas, a 10-year worked example, and why compounding dominates savings and loans.

• How to Calculate Percentage Change

  How to calculate percentage change, increase, and decrease — with formulas, worked examples, and the percent-change vs percentage-points difference.

• Metric vs Imperial Units: History, Differences, and Conversion Guide

  Learn the key differences between metric and imperial systems, why the US uses imperial, and exact conversion factors for length, weight, temperature, and more.

• Understanding BMI

  Learn what Body Mass Index (BMI) measures, the WHO weight categories, the exact formula, and why it's a screening tool—not a diagnosis. Includes limitations.

• How Loan Amortization Works

  How loan amortization splits each payment between principal and interest, why early payments are mostly interest, and how extra payments save money.

• Mean vs Median vs Mode: Definitions, Formulas, and When to Use Each

  Learn the difference between mean, median, and mode. Understand formulas, worked examples with real salary data, and how outliers affect each measure.

• What is Base64? Encoding Explained

  Learn what Base64 encoding is, how it works, and why it's not encryption. Covers 33% size increase, data URIs, JWT, and email attachments.

• How to Convert Kilograms to Pounds (and Back)

  Convert kg to lbs with the exact factor (1 kg = 2.20462 lb), a quick ×2.2 mental trick, a reference table, and common mistakes to avoid.

• JSON Formatter vs JSON Validator: What's the Difference?

  A JSON formatter pretty-prints and indents data; a validator checks syntax and locates errors. When to use each, and what valid JSON requires.

• How UTM Parameters Work (with Examples)

  How the five UTM parameters (source, medium, campaign, term, content) tag links so analytics can credit traffic — with examples and a tag table.

• How to Calculate a Tip (and Split the Bill)

  Learn how to calculate a tip, what percentage to leave in different situations, how to split a bill among friends, and whether to tip on pre-tax or total.

• What Makes a Strong Password

  Learn what actually makes a password strong: why length beats complexity, how passphrases work, and the current NIST SP 800-63B guidance on resets and rules.

• How to Compress an Image Without Losing Quality

  Learn how to compress images without visible quality loss: lossy vs lossless, JPEG vs PNG vs WebP, when to resize, quality sliders, and stripping metadata.

• HEX, RGB, and HSL Color Codes Explained

  Understand HEX, RGB, and HSL color notation: what each one means, how they convert, when to use each, and how alpha controls opacity.

• Kitchen Conversions: Cups, Milliliters, Liters, and Gallons

  Convert cups, tablespoons, fluid ounces, milliliters, liters, and gallons. Learn US vs metric vs imperial units and why kitchen measurements differ.

• URL Encoding (Percent-Encoding) Explained

  Learn how URL percent-encoding works: reserved vs unreserved characters, when to encode query parameters, and common gotchas with spaces, &, +, and #.