Methodology

Our approach

Every calculator on CalculatorBest exists to answer one question quickly and correctly. We use established, published formulas rather than inventing our own, we show the formula on the page that uses it, and we say plainly when a result is an estimate rather than a fact.

Our editorial standard is simple: if we cannot point to a source for a number, a rate, or a rule, it does not go on the page. Where a figure changes annually — tax brackets, contribution limits, statutory rates — we record the tax year so you can see exactly what a result is based on.

Financial and tax calculators

Loan, mortgage, and EMI results use the standard amortisation formula, M = P · i(1+i)ⁿ / ((1+i)ⁿ − 1), where P is the principal, i the monthly interest rate, and n the number of payments. Flat-rate loans are modelled separately and labelled, because a flat rate and a reducing rate with the same headline number produce very different total interest.

Tax calculations apply each country's published progressive bands, then deduct the allowances and credits that country provides. Payroll contributions — FICA in the United States, National Insurance in the United Kingdom, CPP or QPP and EI in Canada, the Medicare levy in Australia, the ACC earners levy and KiwiSaver in New Zealand, USC and PRSI in Ireland, and the cess in India — are added separately and identified in the result.

Sources and tax years in use:

• United States — 2025 federal brackets and standard deductions per the IRS; employee FICA. State and local taxes are not included.
• United Kingdom — 2025/26 bands from HMRC, including Scotland's six separate bands, the tapered personal allowance, and Class 1 National Insurance.
• Canada — 2025 federal brackets and the phased basic personal amount, all ten provincial schedules, CPP/QPP, CPP2, EI, and the Quebec abatement.
• Australia — 2025-26 resident and foreign resident rates, with the Medicare levy.
• New Zealand — 2025-26 PAYE brackets, the ACC earners levy and its earnings cap, and KiwiSaver rates.
• Ireland — 2025 standard rate cut-off, personal and PAYE credits, USC bands, and PRSI.
• India — new and old regime slabs for assessment year 2026-27, with the standard deduction, rebate, and cess.

Tax rules change every year, and provincial, state, and local taxes vary within countries. Treat these results as a well-informed estimate, and confirm anything you rely on with the relevant authority or a qualified adviser.

Health and fitness calculators

• BMI — weight in kilograms divided by height in metres squared, classified using the World Health Organization bands including obesity classes I, II, and III. BMI does not distinguish muscle from fat, which is why we show body fat alongside it.
• Body fat — the US Navy circumference method, using neck and waist for men and neck, waist, and hip for women. It is a field estimate, not a measurement, and its accuracy is typically within a few percentage points.
• Calories and TDEE — the Mifflin-St Jeor equation for basal metabolic rate, multiplied by a standard activity factor. Mifflin-St Jeor is the equation most dietetic bodies recommend for the general population.
• Ideal weight — the Devine, Robinson, Miller, and Hamwi formulas, each shown separately with its original clinical purpose, plus the healthy BMI range for comparison.
• Water intake — a 35 ml per kilogram baseline adjusted for activity, climate, pregnancy, and breastfeeding, with the share normally supplied by food shown separately.

These tools are informational. They are built from population-level formulas and cannot account for your medical history, medication, or body composition. They are not a diagnosis and are not a substitute for advice from a qualified health professional.

Unit conversion

Conversions use exact definitions wherever they exist. An inch is defined as exactly 25.4 mm, a pound as exactly 0.45359237 kg, and a kilocalorie as exactly 4.184 kJ. Where two systems share a name but not a value we show both: a US gallon is 3.785411784 litres and an imperial gallon is 4.54609 litres, and a US cup is 237 ml against a metric cup at 250 ml and a UK cup at 284 ml.

Temperature conversions use the exact offset formulas rather than rounded approximations, so repeated conversions round-trip without drift.

Currency rates

Exchange rates come from public rate feeds and are cached on our server for up to one hour, with a stale copy retained for up to a week if the feed is unavailable. When no live rate can be retrieved, the calculator falls back to a static reference table and says so. Rates are indicative and exclude the spread or fees a bank or broker would apply.

Review and corrections

Tax and rate content is reviewed at the start of each tax year. Health and fitness formulas are reviewed when the underlying guidance changes. Every calculator page shows when it was last updated.

If you find a number that looks wrong, please tell us. Reports that include the inputs you used and the result you expected are the fastest to act on. Email support@calculatorbest.com or use our contact page.

Who we are

CalculatorBest is built and maintained by Shruj Technologies. We fund the site through advertising rather than by selling user data, which is why there is no account to create and no calculator input is stored against your identity.