How it works
The thing you're embedding is the calculator page itself, running inside a frame on your site with its header, sidenotes and footer switched off. There's no second copy of the code and no build step in between, so an embed can't quietly fall out of date.
That has a practical consequence worth knowing about. When a formula gets corrected or a field gets added here, your embed picks it up the next time somebody loads your page. You never have to update the snippet, and the URL you pasted will keep working.
Everything runs in your reader's browser. Nothing they type is sent anywhere, there's no API to call, and no key to keep secret.
Which format
The first five formats all put a working calculator on the page. They differ only in what your publishing tool expects you to paste. If you're editing raw HTML, use HTML. If you're in the WordPress block editor, the WordPress snippet drops in as a proper Custom HTML block. Static site generators like Hugo, Jekyll, Ghost and Astro pass raw HTML straight through, so use Markdown there.
The last three exist because a lot of the internet strips iframes out of user-submitted posts. Forum software nearly always does, and Reddit and GitHub do it with no exceptions. On those, an iframe snippet doesn't render as a broken box, it silently disappears. The link card is an image wrapped in a link instead, so what you get is a card that takes people to the calculator rather than a bare URL sitting in a paragraph.
Discord, Slack, Discourse, Facebook and iMessage are a special case. They build their own preview from a pasted URL, so the Plain link tab is genuinely all you need there.
The credit line
Every snippet includes a short line of text with a link back to the calculator, and it is not optional. Links inside a frame count for nothing, which is why the credit sits outside it in the snippet you paste. That link is the entire business model here - the calculators are free, unlimited and need no account because the link pays for them.
Frequently asked
Is embedding a calculator free?
Yes. There's no account, no key, no usage limit and no fee. The credit line stays in - that's not a request, it's the deal, and it's the reason none of the rest costs anything.
Will the embed break if you change the calculator?
The embed is the live calculator page with its chrome switched off, not a separate copy, so it stays current automatically. If a formula gets corrected or a field is added, your embed picks it up the next time somebody loads your page. The URL never changes.
Why does the iframe get cut off on my site?
An iframe has a fixed height unless something tells it otherwise. The snippet includes a small resize script that measures the calculator and sizes the frame to fit. If your platform strips scripts, set the height by hand instead and add fifty pixels or so of slack for narrow columns, where the fields stack and the calculator gets taller.
My forum strips iframes. What can I use instead?
Use the link card, which is an image wrapped in a link. It can't calculate anything in place, but it reads as a card rather than a naked URL and takes people straight to the calculator. BBCode gets a PNG because not every forum renders SVG in an image tag; Reddit and GitHub get the SVG, which stays sharp on a retina screen.
Can I change the colours or hide part of it?
No. One switch exists on the URL — &bar=0 drops the small dark title bar — but the credit line is not removable, from the snippet or the URL. It is the only thing asked in return for calculators that are free, unlimited and account-free, and it is what pays for them.
Does the embed track visitors?
The embedded page carries the same Google Analytics tag as the rest of the site, so a pageview gets recorded when it loads. Nothing is written to your reader's browser beyond what Analytics sets, no data is passed back to your page, and nothing typed into the calculator ever leaves their browser.
Something's wrong with the embed on my site.
Tell us what's happening and on what platform. Odd rendering in a specific CMS is usually fixable and worth knowing about.