Calculation methodology
How PercentageTools checks calculator results
A reliable calculator needs its formula, implementation, examples, and boundary behavior to agree. PercentageTools uses the process below to keep those pieces aligned and make the result understandable to the person using it.
Define the question and reference value
The calculator starts with a specific user question. The formula identifies whether the reference is a whole, an original value, an accepted value, or the average of two values.
Implement the raw calculation
Formula logic is kept separate from page presentation where practical. The raw numeric result is calculated before display formatting or explanatory text is applied.
Check boundaries and invalid inputs
Tests cover relevant cases such as zero denominators, equal values, decimal inputs, signed values, values above 100%, ordering, and exact classification thresholds.
Match the explanation to the result
The displayed formula, worked example, labels, and FAQs are checked against the same behavior used by the interactive calculator.
Verify the production page
Automated builds and live smoke checks verify routes, canonical URLs, sitemap entries, indexing directives, branding assets, and the custom 404 response.
Rounding and display
Calculations use the numeric inputs before formatting. Results may then be rounded for readability, while tests protect threshold decisions from normal floating-point noise. Financial, classroom, or regulatory settings may require a different rounding convention.
Input privacy
With JavaScript enabled, calculator logic runs in the browser and does not need a separate calculation API request. An account is not required to calculate a result.
Scope and corrections
Calculators are intended for general informational use. When a formula or boundary behavior changes, the corresponding implementation, tests, examples, and explanation should be updated together. Important financial, tax, payroll, academic, or legal decisions should still be checked against the rules that apply to the specific situation.