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