How we build, source, and verify every calculator
We publish 159+ calculators that people rely on for real decisions — loans, taxes, fitness, inheritance. Here is exactly how each one is built, where the formulas come from, and how we keep them accurate.
Why we publish this
A calculator that gives you a number without telling you where the number came from is a calculator you should not trust. We are a small independent team, and the only way we can ask you to trust our outputs is by being explicit about our process. Everything below is what we do internally — written down so you (and Google's quality raters) can audit our approach.
Where our formulas come from
Sources are tiered. We use the highest-quality tier available for the domain.
Government / regulator
Authoritative for jurisdiction-specific rules (tax slabs, registration fees, official conversion factors).
- FBR (Federal Board of Revenue) for Pakistan tax
- SBP (State Bank) for official policy rates
- Excise & Taxation Departments for provincial vehicle/property tax
- NIST + BIPM for SI unit definitions
Standards bodies
Authoritative for measurement and engineering constants.
- ISO standards for unit conversion
- ASTM for construction materials
- WHO + CDC for health thresholds (BMI, BMR, child growth)
- Bureau of Indian Standards for South Asian construction units
Peer-reviewed academic
Used for formulas that require validated coefficients (metabolic equations, body-composition models, statistics).
- Mifflin-St Jeor (1990) for BMR
- Katch-McArdle (1996) for lean-body-mass BMR
- Naegele's rule (1812, still standard obstetrics)
- Tanaka et al. (2001) for max heart rate
Classical religious jurisprudence
Used for Islamic calculations (Faraiz/Warasat, Zakat, Mahr, Qurbani share rules) — sourced from Quran, Sahih hadith collections, and the four major Sunni madhāhib.
- Quran (Surah An-Nisa 11, 12, 176) for inheritance shares
- Hidayah (Hanafi fiqh)
- Bidayat al-Mujtahid (Maliki)
- Standard contemporary fatwa councils for modern application
Our review process
Every calculator goes through these five steps before it ships, and again whenever the underlying source changes.
- 01
Sourcing
Every formula starts from a primary or tier-1 secondary source listed above. We never adapt formulas from random blog posts or competitor sites.
- 02
Implementation
Calculations are implemented in TypeScript with explicit unit handling, edge-case guards (divide-by-zero, negative values, out-of-range inputs), and rounding documented to the appropriate precision for the domain.
- 03
Cross-verification
Results are spot-checked against the source's worked example AND against at least one independent reference (a published calculator from a regulator, a peer-reviewed paper's example, or an authoritative textbook).
- 04
Domain review
Health, financial, tax, and legal calculators include an Educational Disclaimer that clearly states the result is an estimate, the user should consult a qualified professional, and the calculator does not replace personalised advice.
- 05
Update cadence
Tax slabs are refreshed annually after the Pakistan Finance Act. Gold/silver rates are pulled live from a public market data feed (gold-api.com). Other formulas are reviewed whenever the underlying standard changes — when a new WHO guideline issues, when ISO updates a definition, when a Finance Act amends a slab.
What our calculators are not
- They are not personalised professional advice. A BMI calculator does not diagnose obesity; a loan calculator is not your final loan offer; a tax calculator is not your filed return.
- They are not exhaustive of edge cases. Real-world cases (complex inheritance with multiple jurisdictions, tax with multiple deductions, medical conditions with multiple interacting variables) need an expert.
- They are not always current to the minute. Tax slabs update annually, regulators issue new guidance, and we ship updates as fast as we can verify them — but if you're acting on a result the same day a rule changes, double-check before you sign.
Who builds and maintains this
Premium Converters is designed, built, and maintained by Muhammad Salman Saleem (Full-Stack Web Developer). The full bio, sister sites, and contact links are on the About page. For domain-specific review (Islamic jurisprudence, medical guidelines, Pakistani tax law), we cross-reference established authorities and disclose the source on each tool's page.
Found a mistake?
We take accuracy seriously. If you spot a wrong number, an outdated tax slab, an updated medical guideline we should follow, or a misapplied Islamic ruling, please tell us. We fix verified errors fast and credit reporters by name (unless you prefer to stay anonymous).
Report an error