Privacy Policy
The short version: the numbers you type into a calculator never leave your device.
Calculator inputs are never transmitted
Every calculator on this site runs entirely in your browser using JavaScript. When you enter your salary into the mortgage calculator, your weight into the BMI calculator, or your last period date into the pregnancy calculator, that value is processed on your own device and is never sent to us or to anyone else. We could not read it if we wanted to. Closing the tab discards it.
What is stored on your device
The site stores one item in your browser's local storage: your light or dark theme preference, under the key marscalc-theme. It contains the word "light" or "dark" and nothing else. Clearing your browser data removes it.
What we collect
Standard server logs record the page requested, the time, your approximate region, and your browser type. These are used to see which pages are being read and to diagnose faults. We do not attempt to identify individuals from them.
Advertising
This site is supported by advertising. Third-party advertising partners may set cookies or use similar technologies to show ads based on your prior visits to this and other websites. You can opt out of personalised advertising through your advertising provider's own settings, and in many regions you will be shown a consent prompt before any such cookie is set.
We do not share the values you type into calculators with advertisers, because we never receive them in the first place.
Contact form
If you use the contact form, your name, email address and message are transmitted to our form-handling provider so we can read and reply. They are used only to answer you and are not added to any marketing list.
Children
This site is not directed at children under 13 and we do not knowingly collect information from them.
Your choices
You can block cookies entirely in your browser settings; the calculators will still work, though your theme preference will not persist. You can use the site with an ad blocker. You can contact us to ask what we hold about you, though in practice the answer for a calculator user is nothing.
Changes
If this policy changes materially we will update the review date below. Continued use of the site after a change means you accept the revised policy.
This page was last reviewed on 11 August 2026.