Guides

Long-form notes that go with the tools. Read first, then open the calculator.

• How percentage math actually works — Percentage Calculator
• Reading probability results without guessing — Probability Calculator
• Unit conversion factors you can trust — Unit Converter
• Using a browser math calculator carefully — Math & Scientific Calculator
• Net, tax, and gross without mixing bases — VAT / Sales Tax Calculator
• Splitting a bill fairly — Tip & Bill Split
• What ROI does and does not mean — ROI Calculator
• Fixed-rate amortization in plain language — Loan Amortization
• IANA zones and daylight saving — Timezone Converter
• Counting days on calendars — Date Difference
• Five-field cron without the mystery — Cron Expression Helper
• Testing regular expressions safely — Regex Tester
• WCAG contrast ratios explained — Contrast Checker
• HEX, RGB, and HSL for builders — Color Converter
• Keeping proportions when you resize — Aspect Ratio Calculator