CalculatorFox Review: 1,336 Free Calculators You Can Check and Embed

Most online calculators give you a number and ask you to trust it. You can't see how it was worked out, you don't know where the rates came from, and if you put one on your own site, you're stuck with whatever figures it ships with.

CalculatorFox takes the opposite approach. It's a library of 1,336 free online calculators across 23 categories, from mortgages and tax to fitness, construction and chemistry. Every calculator shows its working step by step and cites its sources, and any of them can go on your website for free, with no account and no API key.

TL;DR: CalculatorFox is free to use and free to embed. Every result comes with visible working and named sources. If you publish calculators on your own site, the paid plans let you keep your figures on your account, so changing a rate once updates every page that embeds it. Personal is $29 a year and Advisor, for brokers, accountants and financial advisers who present numbers to clients, is $149 a year.

What CalculatorFox is

CalculatorFox builds practical calculators for money, health, maths, construction, business and everyday decisions. The public calculators are free, work without an account and don't save the figures you enter.

What sets it apart is how each calculator is built. Every calculator declares its inputs, outputs, method, checked examples and sources in code. The page renders a real result and the calculation steps on the server, then adds live updates as you change the figures.

The most popular calculators give a sense of the range:

• Mortgage Payment Calculator
• Margin Calculator and ROAS Calculator, for business, pricing and commerce
• Salary and Annual Income Calculator, for tax, payroll and benefits
• BMI Calculator, for fitness and nutrition
• Loan Calculator, Business Day Calculator and Percentage Change Calculator

Every answer shows its working

Take the mortgage calculator. Enter a $400,000 home with $80,000 down over 30 years at 6.5%, and it doesn't just return a monthly payment. It shows each step:

1. Loan amount = $400,000 - $80,000 down = $320,000 (a loan-to-value ratio of 80%)
2. Principal and interest = $2,022.62 a month
3. No escrow items entered
4. No mortgage insurance on this loan
5. Total monthly payment = $2,022.62

Alongside that you get the total interest over the loan ($408,140.64), the total of payments, the number of payments, the rate per period and more, plus the sources the calculation is worked out from. The working updates live as you change any figure.

For anyone checking a number before making a decision, that's the difference between a result you have to trust and one you can inspect.

How the calculators are checked

CalculatorFox publishes its editorial and calculation policy, and it's stricter than most:

• Sources and worked examples: every calculator must name at least one source and include at least one independently sourced worked example.
• Automated tests: a full test suite recomputes those examples and compares the outputs with the expected values. Shared validation also checks input types, ranges and units.
• What reaches search engines: a calculator is only submitted to search once it has a clear address, an accurate name and explanation, declared inputs and outputs, named sources, a worked example and a checked configuration. Anything that doesn't meet all of those stays reachable by direct link but is kept out of the sitemap.
• No duplicate pages: where two common names describe the same calculation, one page is canonical and the other name redirects to it.
• Text that matches the maths: the explanation on each page is built from that calculator's own inputs, outputs, method and sources, and an automated audit checks every page on each release.

Health, financial, tax, legal and engineering results are presented as informational tools, with clear notes that they don't replace a qualified professional.

Free embeds for any website

This is where CalculatorFox is most useful for founders, publishers and anyone running a content site. You can put any of the 1,336 calculators on your own pages for free:

1. Pick a calculator in the embed builder.
2. Optionally set the figures your readers start from, and fix any field you don't want them to change, such as your own rate or price.
3. Copy three lines of code and paste them into your page.

It works on any site that accepts HTML, including WordPress, Squarespace, Webflow, Ghost, Shopify and plain HTML. Editors that support oEmbed, such as Ghost and Discourse, can embed a calculator just by pasting its address.

A few details matter here:

• No account, no API key, nothing to approve. You can embed as many calculators on as many pages and sites as you like.
• No ads inside the calculator, on any plan.
• No tracking of your readers. The embedded frame sets no cookies and stores no identifiers; CalculatorFox counts views per website and nothing more.

Free embeds carry a small "Calculator by CalculatorFox" credit line under the calculator.

Update a rate once, every embed follows

The standout feature for businesses is hosted figures. Normally, if you publish a calculator with your own interest rate or price baked in, changing that number means editing every page it appears on.

With CalculatorFox, the figures a calculator opens with can be stored on your account instead of in the code on your pages. When the rate changes, you change it in one place and every page that embeds that calculator shows the new figure on its next load. Nobody touches any HTML.

The Advisor plan takes this further: each website gets its own embed token, colour and figures, so a partner site can carry different rates from your own.

Pricing

Every calculator is free. You only pay to keep and present your own numbers.

	Free	Personal	Advisor
Price	$0, no account or card needed	$29 a year (or $5 a month)	$149 a year (or $19 a month)
All 1,336 calculators with working and sources	Yes	Yes	Yes
Ads	Supported by ads	None	None
Saved calculations	5 with a free account	Unlimited	Unlimited
Side-by-side comparisons	2 with a free account	Unlimited	Unlimited
Embeds	Unlimited, with a credit line	No credit line, your colour, views by website, hosted figures	One embed token per website, each with its own colour and figures
Branded reports and client pages	No	No	Yes, under your own name
Priority support	No	No	Yes, within one business day

Personal also adds reusable assumption profiles, PDF and CSV export, and unlimited private links. Every paid plan renews until you cancel and comes with a 14-day money-back promise on any charge. A paid plan never changes a calculator's answer.

See the full comparison on the CalculatorFox pricing page.

Who CalculatorFox is for

• Anyone who needs a quick, trustworthy number. Use any calculator free, with no sign-up, and see exactly how the result was reached.
• Website owners and publishers. Add interactive calculators to your content for free, with no ads inside them and no tracking of your readers.
• Businesses with their own rates and prices. Keep your figures on your account and update every embed at once.
• Mortgage brokers, accountants, financial advisers and contractors. CalculatorFox Advisor lets you work through a calculation with a client, save it under the client's name, and send a PDF or private link carrying your name, contact line and disclaimer.

The bottom line

CalculatorFox is a rare calculator site that shows its work. The library is large, every result can be checked against named sources, and embedding is free with no account, no API key and no tracking of your readers. If you publish calculators on your own site, hosted figures alone can save hours of editing every time a rate changes.

Try any calculator, or build your first embed, at calculatorfox.org.