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Methodology

Overview

This page explains the general methodology behind every calculator on Calcy. Each calculator page also documents its specific formula, variables, and assumptions so you can verify the math yourself.

Formulas

All calculators use established, publicly documented formulas. We do not invent proprietary formulas. Where multiple formulas exist (for example, ideal weight or BMR), we state which formula is used and why. The formula is displayed on each calculator page along with a worked example.

Units

Each calculator specifies the units it accepts and the units it outputs. Where both metric and imperial inputs are supported (for example, BMI and calorie calculators), conversions use the following standard factors:

  • 1 kilogram = 2.20462 pounds
  • 1 meter = 100 centimeters = 39.3701 inches
  • 1 inch = 2.54 centimeters
  • 1 foot = 30.48 centimeters

Output units are always labeled alongside the result so there is no ambiguity about what the number represents.

Rounding

Intermediate calculations use full floating-point precision. Final results are rounded for display purposes only:

  • BMI and similar health metrics: rounded to one decimal place.
  • Currency amounts: rounded to two decimal places.
  • Financial calculations (EMI, SIP, interest): rounded to the nearest whole currency unit.
  • Percentages and GPA: rounded to two decimal places.

Rounding is applied only at the display stage. If you replicate the calculation manually using the documented formula, small differences in the last decimal place may appear due to rounding.

Assumptions

Each calculator documents its assumptions on its page. Common assumptions include:

  • Health calculators assume adult users unless otherwise stated. BMI categories apply to adults aged 20 and over.
  • Finance calculators assume fixed interest rates for the full tenure unless the calculator explicitly handles variable rates.
  • Tax calculators use the standard slab rates for the relevant financial year and do not account for every possible deduction or surcharge.
  • Unit converters use standard international conversion factors.

External Data Sources

The currency converter fetches live exchange rates from the open.er-api.com public API. Rates are cached server-side for approximately three hours to reduce API requests. The last-updated timestamp from the API is displayed on the converter. If the API is unreachable, the converter uses the most recent cached rates and clearly labels them as stale. No exchange rate data is fabricated.

All other calculators run entirely in the browser using the documented formulas. They do not depend on external data sources.

Input Validation

Calculators validate inputs before computing results. Negative values, zero, and non-numeric entries are handled gracefully with clear messages rather than producing misleading output. Where a minimum value is required (for example, height must be greater than zero), the calculator enforces this and informs the user.

Limitations

Every calculator page includes a "Limitations & Considerations" section that explains what the calculator does not account for. We believe that being transparent about limitations is as important as the calculation itself. No calculator on Calcy should be treated as a substitute for professional advice.

Questions

If you have a question about how a specific calculator works, the formula page for that calculator provides the details. For broader questions about our methodology, please contact us.