About SahajTools | Free Statistics Calculators

Who we are

SahajTools is a website of free statistics calculators, published at sahajtools.com. The site is built and maintained by the people who run it, and you can write to them directly at sahajtools@gmail.com.

There is no corporate backstory to tell here. What we can give you is a plain account of what the tools do, how they are built, and what happens to your data, which is what the rest of this page covers.

Our mission

Statistics tools are easy to find and often hard to trust. Many give you a number without saying which formula produced it or which assumptions sit behind it, so you cannot tell whether the answer fits your problem.

We want every calculator here to answer three questions next to the result: what was calculated, how it was calculated, and when that method is appropriate.

What we provide

The site is a directory of 152 calculators in 11 categories. They range from basic probability and summary statistics through probability distributions and regression to hypothesis tests and confidence intervals. Each category has its own page with a short explanation of the key ideas and a list of its calculators:

6 calculators are available now, and the rest are being added one at a time. A page marked “Coming soon” is a placeholder, not a working tool.

When a calculator is published, its page is planned to include the calculator itself, the formula or method it uses, its assumptions and limits, and a worked example. Short question-and-answer sections appear only where there are real questions to answer. Everything is free, and there is no account or sign-up.

Our approach to calculations

Every calculator is meant to go through the same steps before it is published:

Source the formula. We take the formula from several independent references, such as textbooks, university course notes and official statistical documentation, and compare them. If they disagree, we find out why before choosing one.
Keep the maths separate. The calculation code is written apart from the page design so that it can be tested on its own.
Test against known answers. We check results against worked examples with published answers, and against edge cases such as empty input, a single value or a variance of zero.
Say which convention is used. Where a term has more than one accepted definition, for example sample and population variance or the different ways of calculating a quartile, the page states which one the calculator uses.
Check the input. Missing or invalid values produce a plain-language message, not a blank or misleading result.

Accuracy and reliability

We aim for correct results, and we do not claim they are perfect. In practice three things affect reliability more than anything else:

The inputs. A calculator can only work with what it is given. A mistyped value or a wrongly chosen option gives a wrong answer that still looks convincing.
The method. A correct calculation of the wrong statistic is still the wrong answer to your question. Each calculator states what it computes so that you can check it matches.
Numerical limits. Computers store decimals approximately, so very large, very small or nearly identical values can show tiny rounding differences. Where it matters, calculators show more digits or let you choose the precision.

If a result looks wrong, please tell us and include the values you entered and the result you expected. We look into every report.

User-centred experience

The site is free to use, needs no account, and is built to load quickly on phones as well as desktop screens. Text is set for reading, controls can be used with a keyboard, and the site respects your device's reduced-motion setting. We test navigation by keyboard and at screen widths from small phones to wide monitors. The site has not had a formal accessibility audit and we do not claim conformance to a particular standard, so if something is hard to use, please let us know.

Calculators are designed so that you can copy a result, reset the form, and download a PDF summary of your inputs and results. Where a calculator supports it, your entries are kept for the current tab, so a page reload does not wipe your work. The Privacy Policy explains exactly what is kept and where.

Transparency

We try to make it easy to see how the site works and what it does with your information.

Each calculator page names its formula or method and states its assumptions. Where a page relies on a particular reference, we name it.
The Privacy Policy separates what we collect, what we may collect depending on features, and what we do not collect.
The Terms & Conditions set out the limits of the tools in plain language.
The site uses Google Analytics to measure how it is used and shows Google AdSense advertising on some pages. The Privacy Policy says what is collected and how to opt out.

Educational purpose

The calculators are meant for students, teachers, researchers and anyone who needs to check a statistical calculation. They are designed to be learned from: terms are defined, intermediate steps are shown where they help, and each category page explains the main ideas and links to related tools.

They are not a substitute for a course or a textbook. A calculator can give you the value of a test statistic, but it cannot tell you whether that test was the right one for your data. If you use the site for coursework, check what your institution allows.

Responsible use of calculator results

Results on this site are for information and education. They are not statistical, medical, legal, financial or scientific advice.

If a result will feed into a decision with real consequences, such as a clinical decision, an engineering or safety judgement, a regulatory filing, a financial commitment or a published study, verify it independently and involve a qualified professional. The Terms & Conditions cover this in more detail.

Our vision

We would like the site to become a dependable reference for the standard statistics toolkit, from a simple mean or probability up to regression and hypothesis tests, with the same clear layout and the same standard of explanation for every tool. That means more calculators, better guidance on when each one applies, and, over time, written guides on reading results and avoiding common mistakes. We will add these at the pace we can check them properly.

Why you can trust the platform

Trust should rest on things you can check, so here are the ones you can:

You can see how a number is produced. The formula, assumptions and limits are on the calculator's page.
Your inputs stay with you. The site is static, with no server-side code and no database. Calculations run in your browser and are not sent to us, and we do not send the values you enter to Google Analytics or AdSense.
The trackers are disclosed. Pages load Google Analytics and, on some pages, Google AdSense, and nothing else from another company. Fonts and code, including the open-source library some calculators use to generate a PDF, are self-hosted on our own domain rather than loaded from a third-party CDN. The Privacy Policy lists what Google sets and how to refuse it, and you can confirm the requests in your browser's developer tools.
The limits are stated. We say what the tools cannot do, in the Terms and on the pages themselves.
You can reach us. Write to sahajtools@gmail.com to report an error or ask a question. We read every message, though we cannot promise a reply time.

More on getting in touch is on the Contact page.