Help Center & Usage Guide
A guide to using the free online tools on calc-tools.top. All tools run locally in your browser — your data never leaves your device.
How to use this site
Pick a category below, choose a tool, enter your values, and the result updates instantly. Nothing is uploaded; every tool works offline in your browser.
- Privacy: all processing is local, no upload, no sign-up.
- Free: all tools are free to use.
- Bilingual: switch language with the selector in the header.
Category guide
Finance
- Mortgage Calculator — Equal payment + principal, supports commercial + housing fund loans
- Tax Calculator 2026 — Latest 2026 tax rates, calculate after-tax income
- Housing Fund Calculator — Housing fund loan amount + rate calculation
- Car Loan Calculator — Car loan monthly payment + interest
- Loan Comparison — Compare multiple loan plans side by side
- Compound Interest — Calculate compound interest growth
- Overtime Calculator — Overtime pay calculation per labor law
- Percentage Calculator — Percentage calc, increase, decrease, change
- Discount Calculator — Calculate discounted price and savings
- Fuel Cost Calculator — Fuel cost per kilometer calculation
- Electricity Calculator — Calculate electricity bill and usage
- DCA Calculator — Calculate future value of regular periodic investments
- Currency Converter — Convert between major currencies with reference rates
Health
- BMI Calculator — Calculate BMI from height and weight
- Ideal Weight Calculator — Standard weight reference + BMI guide
- Ovulation Calculator — Ovulation + safe period tracker
- Calorie Calculator — Calculate daily calorie needs by height, weight, age and gender
- Pregnancy Calculator — Estimate due date and gestational week from LMP or conception
Lifestyle
- Ovulation Calculator — Ovulation + safe period tracker
- Date Calculator — Date difference, target date, workday calc
- Workday Calculator — Count workdays between two dates, optionally excluding holidays
- Age Calculator — Exact age calculation including zodiac
- Electricity Calculator — Calculate electricity bill and usage
Utility
- Unit Converter — Length/weight/temperature converter
- Password Strength Checker — Test password security with improvement tips
- QR Code Generator — Generate QR codes from text/URL, download as PNG
- Password Generator — Generate strong passwords with custom options
- Random Number Generator — Generate random integers in custom range
- Timestamp Converter — Convert Unix timestamps to dates and back, with seconds/milliseconds and local/UTC
- Fraction Calculator — Add, subtract, multiply and divide fractions and simplify
Image
- Image Compress — Compress images locally without upload
- Format Convert — Convert between JPG/PNG/WebP
- Resize & Crop — Resize and crop images
- Image to Base64 — Convert image to Base64 embedding
- Color Picker — Pick colors from images
- Image Cropper — Drag to crop images with aspect lock, download PNG/JPEG
- Color Contrast Checker — Check WCAG AA/AAA contrast ratio online
Text
- Case Converter — Convert between upper/lower case
- JSON Formatter — Format, compress and validate JSON
- Base64 Encode/Decode — Encode and decode Base64 text
- URL Encode/Decode — Encode and decode URLs
- Text Cleaner — Clean extra spaces and line breaks
- HTML Stripper — Strip HTML tags from text
- Text Diff — Compare two texts for differences
- UUID Generator — Generate UUID identifiers
- Reading Time — Estimate text reading time
- Keyword Density — Analyze keyword density in text
- Word Counter — Count characters/words/paragraphs
- Regex Tester — Real-time match highlight and group parsing
- Markdown Preview — Live Markdown rendering preview
- Simplified-Traditional Converter — Convert between simplified and traditional Chinese