About A2Z Calc

Our mission

A2Z Calc exists to make everyday calculation and unit conversion instantly available to anyone with an internet connection. No sign-up, no installation, no paywall. Whether you are planning a mortgage, following a recipe in a foreign cookbook, doing physics homework, comparing shoe sizes for an online order, or checking the time difference for a meeting across continents, the tool you need should take seconds to find and seconds to use.

We believe accurate, plainly-explained tools should be a public utility, not a subscription product. Everything on this site is free to use, runs entirely in your browser, and works on any device with a modern web browser.

Who's behind A2Z Calc

A2Z Calc is built and maintained by one person: me, Rahman.

I began my professional career as a software engineer near the start of this millennium, back in 2005. The two decades since have taken me through nearly every stage of a software career: writing code, leading teams, and shipping products across multiple countries and industries. The throughline has stayed the same: take a real problem, understand it properly, and build something that works for the person using it, not just for a demo.

This site is a smaller, deliberately scoped project built on top of that experience, combined with a more recent one: using AI to build and ship useful things faster than a solo developer could a few years ago. Rather than start with something large and speculative, I chose to build something small and genuinely useful first: a calculator and converter site with no sign-up, no dark patterns, and no shortcuts on the numbers.

If a tool here saves you a few minutes, or a page explains something more clearly than you expected, it's doing its job. If you spot a mistake or want a calculator that doesn't exist yet, the contact page reaches me directly. I read every message myself.

What you'll find

The site is organised into three broad areas. There are 73 calculators covering personal finance, health and everyday maths; 75 unit converters spanning everyday measurements through to specialist scientific units; and 31 long-form guides that put the tools into context with worked examples and decision frameworks.

52 financial calculators, including mortgage, loan payment, recurring and lump-sum investment, retirement, retirement-expense planning, income tax, investment return (CAGR), inflation, debt payoff, rent vs buy, net worth, take-home salary, home affordability, down payment, budget planner, break-even and credit-card payoff. Browse calculators.
8 health calculators: BMI, BMR and daily calorie needs, body-fat percentage, daily water intake, pregnancy due date and ovulation / fertility window.
13 everyday and math calculators: percentages, discounts, tips, fuel cost, age, date differences, statistics (mean / median / mode / standard deviation), the quadratic equation solver, the triangle calculator and a prime-number checker.
75 unit converters across 9 categories: length, weight, temperature, area, volume, currency, speed, time, energy, pressure, force, power, data storage and transfer; engineering quantities like density, torque and acceleration; specialist heat, fluid, light, electricity, magnetism and radiology units; and lifestyle converters for cooking measurements, clothing sizes, shoe sizes, Roman numerals and time zones. Browse converters.

Who we built it for

The site is built for the way real people use calculators: arriving from a search, getting an answer in seconds, and leaving. That includes students checking homework, parents planning a budget or a pregnancy, professionals running quick numbers for a client, travellers converting currency or shoe sizes, engineers needing a specialist unit conversion, small-business owners modelling their break-even, and anyone with a recipe that calls for millilitres when they only have measuring cups.

Every tool is designed to be usable without reading a manual. Inputs have sensible defaults so you can see how the tool works before changing anything, and every page explains what the calculation does and how to interpret the results.

How we ensure accuracy

Every calculator and converter on the site is implemented using the internationally-recognised formula for its quantity. Mortgage and loan calculations use the standard amortisation formula. Recurring, lump-sum and retirement projections use the future-value-of-annuity and growing-annuity formulas. The body-fat calculator uses the US Navy formula. The pregnancy due-date calculator follows Naegele's rule with cycle-length adjustment. Temperature, volume and other linear conversions are based on the SI definitions and CODATA-recommended values.

We test each tool with reference values before publishing it, and we welcome corrections from users who spot anything inconsistent with authoritative sources. That said, results from any calculator are estimates for general guidance. For financial, medical, legal, engineering or tax decisions with real consequences, please consult a qualified professional who can take the specifics of your situation into account.

Data sources and standards

Conversion factors come from the International System of Units (SI) and the international standards bodies that maintain them: the BIPM (International Bureau of Weights and Measures), NIST (US National Institute of Standards and Technology), and ISO. Where multiple national standards exist (for instance US, imperial and metric variants of cups, fluid ounces or tonnes), we keep them clearly labelled so you can pick the right one.

The currency converter uses a public exchange-rate API that aggregates rates from central banks and major market sources, refreshed regularly. Time-zone calculations use the IANA Time Zone Database (the same source your operating system uses) so daylight-saving transitions are handled correctly. Tax-bracket content on the income-tax calculator is intentionally editable: tax rules vary by country and change every year, so the calculator accepts any progressive bracket structure you enter.

Editorial standards

On the pages where the numbers carry real consequences, health and tax in particular, we try to be explicit about where each figure comes from rather than asking you to take our word for it. Those pages carry a Sources block linking the body that actually publishes the threshold, and a Last reviewed date showing when the content was last checked. Every outbound source is opened and verified before it is published, and we name what each one supports rather than citing it vaguely.

Where an authority declines to state something, we say so instead of simplifying. The BMI page is the clearest example: the WHO's 2004 expert consultation on Asian populations identified four public health action points and explicitly stopped short of setting a single replacement cut-off, and the page reports it that way even though a cleaner two-number version would read better.

The health calculators implement published thresholds from the WHO and equivalent bodies. They are screening tools, not diagnostic ones, and they are not reviewed by a clinician, so they describe what a measurement means and deliberately avoid setting targets, prescribing calorie deficits or suggesting timelines. For anything affecting your health, a doctor or registered dietitian who can see your full picture is the right source, not a formula.

Privacy and how the site is funded

We do not require accounts, and the values you type into the calculators and converters stay in your browser and we never send them anywhere. The one exception is a result link you open or share, which carries its numbers in the page address. The site is funded by unobtrusive display advertising; see the privacy policy for the full details on cookies and third-party services. We do not sell user data and we never will.

Get in touch

If you spot a bug, want a new calculator added, or have a correction to one of the formulas or data tables, please get in touch via the contact page. User suggestions drive a lot of what we build next.