Answers you can check
A calculator that only prints a number leaves you guessing whether you asked the right question. Each calculator here shows
the formula it used next to the result, 20 ÷ 100 × 150 = 30, “9 months, 11 days (284 days)”, “MCMXCIV = M + CM +
XC + IV”. That makes it easy to spot a mix-up, explain the result to someone else, or copy the method into a spreadsheet.
Precision details that matter
- No floating-point noise. Results are rounded to remove artefacts like 0.30000000000000004 without hiding real decimals.
- Calendar-correct dates. Leap years and month lengths are handled, and adding a month to January 31 lands on the last day of February rather than spilling into March.
- Standard Roman numerals. Non-standard spellings like IIII or IC are flagged with the correct form instead of being silently accepted.
All 3 tools in this category
- Date Calculator: Count the days between two dates, or add and subtract days, weeks, months, years and business days from any date.
- Percentage Calculator: Work out X% of Y, what percent one number is of another, percentage change, increase, decrease and difference, with the formula shown.
- Roman Numeral Converter: Convert numbers to Roman numerals and back, with a step-by-step breakdown, dates in Roman numerals and values up to 3,999,999.
Other categories
- Data & Format: JSON, XML, YAML, CSV, SQL, HTML and Markdown, format, view, convert and diff.
- Encoding & Crypto: Base64, URL, JWT, hashes, UUID, binary, QR codes and passwords.
- Dev Productivity: Regex, cron, timestamps, word counter, case converter, lorem ipsum, subnets and more.
- Frontend & Design: CSS generators, image compression, SVG to PNG, favicons and px to rem.
- Text Tools: Morse code, small text, fancy fonts and everyday text clean-up.
- Generators: Random numbers, words, names and realistic test data.