What is Howdeedo?
Howdeedo is a calculator website and deterministic computation platform. Same inputs and version produce the same outputs, with formulas and assumptions documented on each page and in our APIs.
Frequently asked questions
Quick answers about accuracy, privacy, APIs, and how to use Howdeedo. For legal detail, see Privacy, Terms, and Disclaimer.
Getting started
Are your calculators free?
Yes. You can use the web calculators without an account. We may show ads if you accept cookies; the math is not influenced by advertisers.
Do I need to create an account?
No for normal web use. Optional accounts exist for developers who want API keys and higher usage limits; anonymous visitors can use calculators and read trust pages without signing up.
Where can I find all calculators?
Browse the full list on our All calculators page or the site map, or start from the home page by category.
How do I choose the right calculator?
Start from the category that matches your question (finance, health, math, etc.), then read the short description on each tool. If two calculators overlap—mortgage vs loan, for example—pick the one whose inputs match what your lender or teacher expects.
Do calculators work on mobile?
Yes. Layouts are responsive. For long forms, landscape or a larger phone can make numeric entry easier, but all core flows work on small screens.
Can I use Howdeedo offline?
You need a network connection to load pages from our servers. After load, some interaction happens in your browser, but fresh visits and API calls require connectivity.
How do I share a result with someone else?
Use the share or copy-link control on the result when available; many calculators sync inputs into the URL so the link reproduces what you entered. For maximum reproducibility, use a citation record page (/r/...) when the calculator offers one.
Using calculators
How do I use the mortgage calculator?
Enter loan amount, annual interest rate, and term in years. The result is principal and interest only—add taxes, insurance, and HOA separately for total housing cost. Adjust rate or term to compare scenarios; use our house affordability calculator if you are budgeting from income.
How should I interpret BMI results?
BMI is a population-level screening metric from height and weight. It does not measure body fat directly, muscle mass, or health status. Use it as one input alongside how you feel, activity, and advice from a clinician—not as a diagnosis.
What is compound interest vs simple interest?
Simple interest applies only to the original principal. Compound interest applies to principal plus accumulated interest, so growth accelerates over time. The same nominal rate compounds to a higher balance than simple interest when held for multiple periods.
Why does my result differ from my bank’s app?
Different assumptions: day-count conventions, rounding, fees, escrow, promotional rates, or credit tier. Compare the formula and assumptions we show to the disclosure from your lender; small input differences also change outputs.
What does “solve for” or inverse mode mean?
Some calculators let you hold an output fixed and back out an input—for example, loan payment given rate and term, or price given discount. If a tool offers it, read the field labels: the unknown is computed from the numbers you provide.
Are tax calculators a substitute for filing taxes?
No. Federal and state tax tools here are educational estimates. Real liability depends on credits, AMT, withholding, and forms we do not model. Use official IRS tools or a professional for filing decisions.
How do unit converters pick precision?
We use defined conversion factors and round for display. For science or engineering, confirm against a primary standard if precision at the edge of the factor matters.
Can I print or save a page?
Use your browser’s print or save-as-PDF. For citations, prefer the page URL, date accessed, and any version string shown in the methodology section or API response.
Accuracy & trust
Do you store what I type into calculators?
For typical use in the browser, inputs are processed with our published formulas—we do not store calculator inputs on our servers as a user profile. Shareable links encode inputs in the URL. If you use our public API, we may log technical data like IP and endpoint for rate limiting and security—see our Privacy Policy.
What does deterministic mean here?
It means repeatability: given the same calculator version and inputs, you get the same outputs. That is what makes results easier to verify, share, and cite than ad-hoc spreadsheet copies.
How accurate are online calculators?
Accuracy depends on the methodology and whether your situation matches the stated assumptions. We document assumptions on each page; you should still verify any outcome that matters for health, safety, or major financial decisions.
Why do different websites show different answers?
Rounding, formulas, tax years, fees omitted, or different definitions (APR vs APY, taxable vs gross income). We publish formula identifiers and assumptions so you can see what we implemented; always compare like with like.
Can I cite your calculator results?
Yes. Use the calculator URL, the date you ran it, and any version or record metadata shown on the page. For API use, responses include fields that support reproducibility.
Is this financial or medical advice?
No. All calculators are informational tools only. For money, health, or legal decisions, consult a qualified professional. See our Disclaimer and Terms.
What is an assumption on a calculator page?
Assumptions are the simplifications we had to make so the math is tractable—fixed rate, no PMI, standard deduction only, etc. When your real situation violates an assumption, treat the output as directional, not exact.
How often is content reviewed?
Major methodology and editorial copy are reviewed on a rolling basis; calculator pages show a last-reviewed date and engine version near the methodology block. Tax and rate-sensitive tools are updated when brackets or defaults change.
API & technical
Do you have an API?
Yes. Each calculator has a corresponding API route. See the OpenAPI spec at /api/spec and /llms.txt for discovery and examples.
What are API rate limits?
Anonymous access is rate-limited to keep the service fair and stable. Limits are subject to change; see our access documentation. Higher usage may require an API key.
What is in a calculator API response?
Typically inputs echo, outputs, formula summary, assumptions, version, and links or fields that support citations. Exact shape is documented per route in the OpenAPI spec.
Can I use the API without JavaScript?
Yes. Send HTTP requests with JSON bodies as documented. The web UI is optional; agents and servers can call the API directly.
Do you offer MCP or CLI tools for agents?
Yes. We publish an MCP server and CLI for discovery and deterministic calls alongside the HTTP API. See repository documentation and /llms.txt for entry points.
What is llms.txt?
A machine-readable index of key URLs and policies for AI systems and developers. It complements our public API and sitemap for discovery.
Where is the calculation engine version defined?
Published responses and methodology blocks include a version string tied to our shared calculation packages. When we change formulas in a breaking way, version increments so old citations remain interpretable.
Privacy & legal
Why do you ask about cookies?
We use cookies and similar technologies for optional analytics and advertising (e.g. Google AdSense) only after you opt in, where required. Essential functionality does not depend on ad cookies.
Who do I contact for privacy questions?
Email contact@howdeedo.com or use the contact form. Our Privacy Policy describes data practices in detail.
When I open a shareable calculator link, can a server see my inputs?
Loading any page sends the request URL—including query parameters if present—to our hosting provider as part of normal web delivery. Access logs may include the path, query string, IP address, and browser type for security and operations. That is different from storing your inputs in an application database. We do not use that data to build advertising profiles from calculator inputs. Details are in our Privacy Policy.
What are citation record pages (URLs starting with /r/)?
They are pages that show a specific saved calculation (inputs, results, formula version) for sharing and citing. The site needs the URL query parameters to verify the record hash and render the page. The same general logging applies as for any page request—see the Privacy Policy.
How does the contact form work?
Submissions are delivered through Web3Forms, a third-party form service, so we can receive your message. Avoid sending unnecessary sensitive personal, health, or financial information.
Do you sell my data?
We do not sell personal information as defined in applicable privacy laws. Advertising partners may process limited data when you consent to ads; see the Privacy Policy for categories and choices.
How do I request accessibility help?
See our Accessibility statement for our approach and contact paths. We welcome specific reports (URL, browser, assistive tech) so we can reproduce and fix barriers.