Methodology, assumptions and accuracy
Transparency matters: every calculator uses an explicit mathematical rule, and every result has limits.
Core formulas
Percent of amount: (p ÷ 100) × amount. Part as percent of whole: (part ÷ whole) × 100. Percent change: (new − original) ÷ |original| × 100. Reverse percentage: final ÷ (1 + p/100).
Commerce formulas
Discounted price = original × (1 − discount/100). Estimated taxed total = discounted price × (1 + tax/100). Tip total = bill × (1 + tip/100). Gross profit = selling price − cost; margin = profit ÷ selling price × 100; markup = profit ÷ cost × 100.
Growth formula
Compounded value = start × (1 + rate/100) ^ periods. The calculator supports whole-number periods from 0 to 1,000 and percentage rates of at least −100%.
Edge cases
Zero denominators are reported as undefined. Reverse calculations cannot recover a unique original after a 100% decrease. Negative and unusually large inputs may be mathematically meaningful but not economically realistic; use judgment.
Charts
The percentage bar illustrates a selected part on a 0–100% visual scale. Values outside that range are clipped for display only; the mathematical result remains unchanged. The change comparison uses absolute bar widths for relative magnitude and labels the signed values separately.
Accuracy and verification
All calculations occur locally in JavaScript. Decimal floating-point precision and rounding conventions may cause tiny discrepancies. Displayed results are rounded for readability. For contracts, invoices, tax filings and investments, confirm values with the relevant institution.
Editorial maintenance
We periodically review formulas, explanations and user experience. These tools do not depend on a specific tax or financial rate schedule: you supply the rate, and it is your responsibility to verify it.