Information
Methodology and sources
Right Calc answers one question per page. This page explains how each answer is worked out, where the data comes from and what its limits are.
How results are calculated
Every formula runs on our server, in one place. The page you see without JavaScript and the live result as you type come from the same code, so they cannot disagree. The page always opens already calculated with example values; it never shows a made-up result.
Division by zero, values out of range and absurdly large results become a message on the field that caused them, never a blank, NaN or INF.
How results are checked
Each calculator has automated tests with reference cases worked out by hand, plus extreme values and invalid input. A change that alters a reference result does not ship. Monetary correction was also compared with the Central Bank of Brazil’s Citizen’s Calculator for IPCA, Selic, CDI and both savings rules.
Formulas and sources
| Calculator | Method and source |
|---|---|
| Compound interest, simple interest, equivalent rate, investment goal, financial calculator | Standard financial-mathematics formulas, shown step by step on each page. |
| Loans (Price and SAC) | Price: equal payments, PMT = PV · i ÷ (1 − (1 + i)−n). SAC: constant amortization of PV ÷ n, with interest on the outstanding balance. |
| Inflation (US) | CPI-U, not seasonally adjusted (series CPIAUCNS), from the U.S. Bureau of Labor Statistics. Same series and same calculation as the BLS inflation calculator: amount × CPI(end month) ÷ CPI(start month). |
| Monetary correction (Brazil) | Time series from the Central Bank of Brazil (SGS): IPCA, INPC, IGP-M, IGP-DI, IPCA-E, IPC-Brasil, IPC-SP, Selic, CDI and savings. Checked against the Central Bank’s own Citizen’s Calculator. |
| BMI | Weight ÷ height². Adult categories of the World Health Organization; the CDC uses the same cutoffs. |
| Daily calories | Basal metabolic rate by the Mifflin–St Jeor equation (1990) × an activity factor. |
| Ideal weight | Healthy BMI range (18.5 to 24.9) plus the classic height formulas: Devine (1974), Robinson (1983), Miller (1983) and Hamwi (1964). |
| Body fat | US Navy method (Hodgdon and Beckett, 1984) from body measurements; categories from the American Council on Exercise. |
| Due date | Naegele’s rule: first day of the last menstrual period + 280 days. |
| Unit converters | Exact definitions of each unit in terms of the SI base unit (NIST SP 811, and the 1959 international agreement for the yard and the pound). |
| Percentages, math, dates and everyday | Standard arithmetic, algebra and calendar rules. |
Each calculator page also explains its own formula in the “how it works” section.
Limits
Results are estimates for information. They do not include taxes, fees, insurance, contract terms, medical history or local rules, and they are not financial, medical or legal advice. See the Terms of Use.
Corrections and updates
Found a wrong result or a source that is out of date? Tell us on the Contact page with the calculator and the values you entered. The date above is the last review of this page, and each calculator page shows when its text last changed.
Who is behind it
Right Calc is a product of Dantai.