Why we show the formula
Most calculator sites give you a number and that is it. We think you should see how the answer was calculated, so you can sanity-check it and learn the math for next time. Every result on this site is accompanied by the plain-language formula we used and, where relevant, the intermediate steps.
If we change an input, you can watch the result change and reason about why. If you disagree with our approach, you have enough information to recalculate by hand. If you are learning the subject, the formula itself is part of the answer.
How we source
Every calculator page lists its sources. For health tools, that means peer-reviewed clinical references (BMI cutoffs from the WHO, calorie formulas from Mifflin-St Jeor, macro ratios from the Academy of Nutrition and Dietetics). For finance, we cite the underlying formula (amortization, compound interest, DTI) and, where jurisdiction matters, we link to the relevant tax authority.
When a figure is a reasonable default rather than a law of nature (for example, an assumed inflation rate in a retirement projection), we mark it clearly and let you override it. Defaults are defaults; your inputs win.
How we verify
Each calculator is checked against at least two independent sources: a textbook or spec document, and an independent reference implementation (typically a spreadsheet, a published calculator from a regulatory body, or an authoritative third-party tool). We record the test cases we use and re-run them whenever the underlying formula is touched.
Some of our tools cover domains where small regional differences in convention matter (GPA scales, tax brackets, unit systems). Where that is the case, we offer the relevant choices rather than picking one and hoping.
Privacy and what happens to your inputs
Every calculator runs in your browser. Your salary, your weight, your savings balance, your email list size — none of it leaves your device. We do not send it to our servers. We do not store it. We cannot log in and look at it, because it was never ours.
We use lightweight analytics (Google Tag Manager + GA4) to count how many people visit which pages, which is gated behind the cookie consent banner and anonymized. See the privacy policy for the full details.
What we do not do
We do not give financial, medical, legal, or other professional advice. Our calculators are correct arithmetic on the inputs you give us. They do not know your full situation and they should not be the last step in any decision that matters.
We also do not chase engagement. There are no exit-intent popups, no "wait! here is a discount," no account requirement to see the answer. You came here to do math. We try to stay out of your way.
When we get things wrong
We do, sometimes. If you spot a bug, an outdated tax bracket, a wrong citation, or anything else, please tell us via the contact page. Reports that come with a reproduction case go to the top of the queue.