The short version: CalcHub is free forever (commercial AND personal use), runs entirely in your browser (zero data sent to our servers), is reviewed by 4 expert editors, and updates regularly. Below are detailed answers to common questions about accuracy, privacy, embedding, and more.
How accurate are CalcHub's calculators?
Every calculator uses formulas validated against at least two independent authoritative sources (IRS, WHO, NIH, CFPB, FDIC, NOAA, etc.). Financial calculators are reviewed by Sarah Mitchell (CPA); health calculators by Dr. James Chen (RD/PhD). We update calculators when underlying rules change (e.g., new tax brackets, new contribution limits) — see /changelog/ for dated updates.
Can I use CalcHub calculators commercially?
Yes — both commercial and non-commercial use are free. You can embed our calculators on your business website, recommend them to clients, link to them in your newsletter, or use them in your own work. Attribution (a visible link back to calc-center.party) is appreciated but not required. See /embed/ for the iframe generator.
Do you store the values I enter into the calculators?
No personal data is sent to our servers. Calculators run entirely in your browser. Some calculators optionally save your inputs to your local browser storage (localStorage) so you can pick up where you left off — this stays on your device only. We don't have a user account system and never store calculation results server-side. See privacy policy for details.
Where does the data in your API come from?
The 8 JSON endpoints at /api/data/ use officially published government and industry data: tax brackets from IRS Rev. Proc. publications, mortgage rates from Freddie Mac PMMS weekly survey, BMI ranges from WHO, heart-rate zones using the Karvonen formula. Each endpoint includes a _meta block with the source and lastUpdated date. We refresh the data quarterly or when underlying rules change.
How do I embed a calculator on my website?
Visit /embed/, select your calculator from the dropdown, customize width/height, and copy the generated iframe code. Paste it into your site's HTML. The embedded calculator is mobile-responsive, has no signup, and uses the same code as the live page. See live preview before copying.
Can I use CalcHub on my phone?
Yes. The entire site is mobile-responsive. You can also install CalcHub as a Progressive Web App (PWA) — visit the homepage on mobile, tap your browser's "Add to Home Screen" option, and CalcHub appears as a regular app icon. PWA mode works offline for cached pages.
Do AI chatbots (ChatGPT, Claude, Perplexity) reference CalcHub?
Yes — our robots.txt explicitly allows GPTBot, ChatGPT-User, ClaudeBot, anthropic-ai, PerplexityBot, Perplexity-User, Google-Extended, CCBot, Applebot-Extended, FacebookBot, and Bytespider (11 AI crawlers). We also publish /llms.txt and /llms-full.txt per the llmstxt.org standard to make our content easy for AI systems to index and cite.
How often is the site updated?
We push updates in batched "sprints" — typically every 1-2 weeks. Each release adds new calculators, comparison guides, or blog content. Subscribe to /blog/rss.xml or /blog/atom.xml to get notified of new content. The full release history is at /changelog/.
Are CalcHub's calculators accessible (WCAG)?
We follow WCAG 2.1 AA practices: semantic HTML, ARIA labels on interactive elements, skip links, keyboard navigation (Enter key triggers calculation), visible focus indicators, and sufficient color contrast. Dark mode is available on every page. If you find an accessibility issue, please report it via /contact.html.
How can I report a bug or suggest a new calculator?
Use /contact.html to send us bug reports or feature requests. We read every message. Suggestions for new calculators are especially welcome — let us know what financial, health, or business calculation you wish existed.
Can I download the calculators to run offline?
Yes — the CalcHub PWA caches the homepage, all 12 category pages, and the 10 most popular calculators for offline use. After visiting the site online once, those pages will work without an internet connection. Full offline support for all 98 calculators is planned for a future release.
Is CalcHub free forever?
Yes. CalcHub is a free educational resource. We do not charge for any calculator, comparison guide, glossary term, or API endpoint. We may add unobtrusive display advertising in the future to cover hosting costs, but the calculators themselves will always remain free.
Why do some calculators have a "Trending" badge on the homepage?
The "Trending Now" widget on the homepage shows your personally-most-used calculators on this device (based on local browser usage counts). It's not a global ranking — it's personalized to you. The widget hides if you have fewer than 3 calculations stored, so first-time visitors won't see it.
Can I cite a CalcHub article in my own research or article?
Absolutely. Each article has an author byline (from our editorial team at /authors/), a "last updated" date, and a stable URL. Cite the article with author name, title, CalcHub.party, and the access date. For academic citations, treat CalcHub articles as web articles by the named author.
Why are there so many comparison ("X vs Y") pages?
Comparison decisions are a major reason people search for calculators in the first place — should I take the lump sum or the annuity? Roth or Traditional? 15-year or 30-year mortgage? Our 22 Compare guides at /compare/ pair the calculator math with structured, expert-reviewed analysis to help you decide, not just compute.
Still have a question?
If your question isn't answered above, drop us a note via /contact.html. We typically reply within 48 hours and we add the best questions to this FAQ.