Methodology & Sources

How we build each calculator

Every calculator on calculadora.work follows a five-step process to ensure accuracy, clarity, and real-world usefulness. This page transparently documents that process.

1. Identification and research

Each calculator starts from a real user need, identified through search trend analysis, direct feedback, and community demand. We then research the correct formula by consulting primary sources: scientific articles, technical standards, official regulations.

2. Formula validation

Each formula is cross-checked against at least two independent sources. For critical calculators (health, tax-related finance), we review with professionals before publishing.

3. Technical implementation

The calculation runs entirely in your browser (client-side JavaScript). No data is sent to servers. We use number parsers that accept Brazilian (1.234,56) and international (1,234.56) formats to avoid subtle errors when pasting values.

4. Linguistic review

Content in three languages, written by humans and reviewed by native speakers. We don't use machine translation for primary content.

5. Continuous maintenance

Tax tables, financial indices, and regulatory data are reviewed annually. The date of the last review appears on each affected calculator.

Official sources we use

Health and fitness

• BMI and classification: World Health Organization (WHO) — cutoffs 18.5 / 25 / 30
• TDEE/BMR: Mifflin-St Jeor equation (1990), considered gold standard by the Academy of Nutrition and Dietetics
• Heart rate: Tanaka formula (208 − 0.7 × age)

Finance (Brazil)

• INSS, IRRF, FGTS: Official tables from Receita Federal and Ministry of Labor, updated yearly
• Selic, IPCA: Central Bank of Brazil and IBGE
• Price system (PMT): classic financial math, PMT = PV × i / (1 − (1+i)^-n)

Finance (Spain)

• IRPF, VAT, Modelo 303/130: Spanish Tax Agency (AEAT)
• Social Security contributions: Tesorería General de la Seguridad Social (TGSS)
• Self-employed quota (RETA): income-based tiered system (Royal Decree 504/2022)

Unit conversions

• SI (International System): BIPM (Bureau International des Poids et Mesures)
• Inch/foot/yard/mile: 1959 international definitions (1 in = 25.4 mm exact)
• Energy: joule per CODATA 2019; thermochemical calories (1 cal = 4.184 J exact)

Not professional advice — disclaimer

The calculators on calculadora.work are educational and estimation tools. They do not replace professional medical, legal, accounting, or financial advice. For important decisions — medical diagnoses, tax filings, loan contracts — always consult a qualified professional.

Formulas are provided "as is" and may contain errors. If you spot a discrepancy, please report it to roberto@santacroce.xyz and we'll investigate immediately.