About YiJianSuan
Professional, accurate, instant calculators — free for everyone
Last updated: August 2025
Who We Are
YiJianSuan is a free online calculator website offering 459 professional tools across 10 categories — math, finance, health, unit conversion, date & time, lifestyle, developer tools, geometry, business & tax, and science — plus 201 in-depth usage guides.
We started this project for a simple reason: finding a trustworthy calculator online is surprisingly hard — wrong formulas, inconsistent units, more ads than tool, mandatory sign-ups. We believe accurate calculation should have no barrier, so we sweat every detail: formulas traced to official documents, results with worked steps, conflicting conventions shown side by side, and your data never leaving your browser.
Our Four Principles
- Accurate & traceable: every formula cites an authoritative source (national standards, statutes, primary papers); every page discloses its review date and sources
- Free with no barrier: instant access, no sign-up, no limits, no paywalls — across the entire library
- Privacy first: all computation runs locally in your browser; your inputs are never uploaded
- Open by design: Chinese/English bilingual, PWA installable, open REST API and llms.txt — built for humans and AI alike
What We Cover
10 categories and growing — from everyday essentials to professional depth:
| Category | Scope | Representative Tools |
|---|---|---|
| Math | Arithmetic to advanced math | Scientific calculator, equation solver, matrix, normal distribution |
| Finance | Personal finance to derivatives | Mortgage, compound interest, income tax, Black-Scholes, DCF |
| Health | BMI to clinical formulas | BMI, TDEE, creatinine clearance, eGFR, pregnancy weight |
| Conversion | Daily to engineering units | Length, power, flow rate, thermal units, Chinese units |
| Date & Time | Age to lunar calendar | Age, business days, lunar conversion, moon phase, ISO week |
| Lifestyle | Renovation to travel | Electricity cost, fuel, tile quantity, baggage rules, curtains |
| Developer | Encoding to encryption | JSON formatter, regex tester, JWT decoder, AES encryption |
| Geometry | Solve from any known values | Triangle, annulus, spherical cap, frustum, regular polygon |
| Business & Tax | Invoices to startup metrics | VAT, corporate income tax, CAC/LTV, break-even |
| Science | Mechanics to circuits | Ohm’s law, projectile, dew point, voltage drop, centrifuge |
Our Bar for Every Tool
We reject bare "one input, one button" tools. Before launch, every calculator must ship with:
- Real formulas: cross-verified by the review team — never back-of-envelope estimates
- Multi-directional solving: solve for any unknown from any knowns wherever possible (e.g. full-combination geometry solvers)
- Worked steps: complete calculation steps attached to every result — verifiable and educational
- Authoritative tables: official standards (BMI cutoffs, tax brackets, heart-rate zones) presented alongside
- Visualization: proportion bars, scale markers, geometric diagrams — results you can read at a glance
- Validation & edge cases: negatives, zero and extremes get explicit feedback — never silent failures
- Full bilingual support: every tool fully translated; China-specific concepts keep Chinese terms with notes
Editorial Team
All content is created by the YiJianSuan Editorial Team and verified by the YiJianSuan Review Team. Every calculator passes formula-correctness, edge-case, and unit-convention checks before launch. Every guide ships with a core answer, comparison tables, worked examples, a misconception list, and FAQs — with review dates and sources disclosed. See our Editorial & Review Policy for details.
- YiJianSuan Editorial: topic research, formula implementation, worked examples, writing
- YiJianSuan Review Team: cross-verification of formulas, official-standard checks, periodic re-review
Data & Formula Sources
Authoritative standards referenced across the site come from official public documents, including:
- National standards and government publications (GB/T, central bank, tax authorities)
- International bodies: WHO, IRS, IOM, ACSM, IUPAC and more
- Academic literature: Mifflin-St Jeor, CKD-EPI 2021, Black-Scholes and other primary sources
- Current statutes: labor law, individual income tax law and related regulations
Open Ecosystem
- Open API: GET /api/v1/calc/[slug] with an OpenAPI 3.0 spec — free for developers and AI agents
- llms.txt: a site manifest for AI crawlers, with JSON-LD structured data across the site
- PWA: installable on phones and desktops, works offline
- Browser extension: quick-access popup for high-frequency tools on Chrome / Edge