Methodology & Accuracy

Last updated: September 10, 2026

                Core principle: Every tool runs locally in your browser, with open and verifiable formulas. This page explains how each tool works, the formulas it uses, key assumptions, and accuracy limits — so you can judge whether a result fits your situation.
            

1. How we work

All calculation logic runs entirely in front-end JavaScript — no input is uploaded. Each tool is built on a well-known published formula and regression-tested against known examples. If you question any result, please tell us via the contact page.

2. Calculator formulas & assumptions

BMI calculator: BMI = weight(kg) ÷ height(m)². Uses the WHO classification (underweight / normal / overweight / obese). Units are converted automatically; results show two decimals.
Compound interest: A = P(1 + r/n)^nt, where P is principal, r is annual rate, n is compounding frequency per year, t is years. Defaults to annual compounding; switchable to monthly / daily.
Mortgage calculator: Equal monthly installment formula, monthly payment = principal × monthly rate × (1+monthly rate)^terms ÷ ((1+monthly rate)^terms − 1). Rate and term come from your input; excludes tax and insurance.
Income tax calculator: Estimates using China's comprehensive-income progressive brackets, with simplified assumptions for the basic deduction and common special deductions; final figures follow your tax filing.
Date calculation: Gregorian day-difference, supports cross-year and leap years. Returns calendar days; does not apply business-day rules (use the separate workday tool).
Housing fund loan: Estimates using rates and quota rules published by local housing-fund centers; actual quota follows local policy.

3. Image & text tools

Image tools (compress, convert, resize/crop, Base64, color picker) run entirely locally via the browser Canvas / File API — files never leave your device. Text tools (word count, JSON formatter, Base64, UUID, text diff) are deterministic local algorithms with reproducible results.

4. Accuracy & limitations

Floating-point math carries negligible rounding error; we round displayed results. For amounts, taxes, or health metrics, results are for reference only and not professional advice. Policy-driven tools (tax, housing fund) change with regulations; we label the applicable scope and update periodically.

5. Data sources

Formulas come from public authoritative standards (WHO BMI classification, rates published by the central bank / housing-fund centers, the Individual Income Tax Law). We label key assumptions on each tool page; if you have a more authoritative source, let us know.

6. Contact us

Found a wrong formula or assumption? Tell us via the contact page and we'll verify and update promptly.