How we check our numbers

1Where our numbers come from

We use the most direct source available, in this order:

1. The official source: laws, regulations and agency publications, such as IRS publications and revenue procedures, Department of Labor rules, SSA wage-base notices and state revenue department rate tables.
2. The company's own terms: for platform and payment fees (eBay, Etsy, PayPal, Stripe, Shopify and others), their published fee pages.
3. Published datasets: for industry averages and wages, we name the dataset and its date, for example NYU Stern's (Damodaran) margins by sector, labelled as US listed companies, or Bureau of Labor Statistics wage data. A benchmark is a guide, not a rule, and you can replace it with your own figure.

Each calculator lists the sources it uses at the bottom of the page, with links.

2Dated checks

Calculators that depend on a rate that changes show a line such as "US rates · checked 17 Oct 2026" under the title. That date means we opened the official page and confirmed the figure on that day. We only change the date when we re-check; we never move it forward to make a page look fresh.

If we can't open or confirm an official page, the calculator does not show a checked date, even if the figure is probably right.

3How formulas are built and tested

• Every calculator is a small, self-contained formula with its inputs, assumptions and steps written out on the page.
• Each one has worked examples worked out by hand, and automated tests that must reproduce them to the cent. The whole set of more than 2,000 tests runs before every release.
• We also open the calculators in a real browser, on desktop and phone sizes, to check that they give a result, react to changes and show no errors.
• Money is rounded to the cent unless the official source rounds differently.

4When we re-check

• Every year when new tax-year figures are published (usually October to January), for tax, payroll and retirement calculators.
• When a platform announces a fee change, for seller and payment fee calculators.
• When a reader reports a problem, straight away.

5What a calculator can't know

A calculator only knows what you type in. It can't see your full tax situation, state rules that apply only to you, or a contract's fine print. Results are estimates for planning and are not tax, legal or financial advice. For decisions that matter, check with the official source or a qualified professional. See our Terms of use.

6Ads and independence

The site will be paid for by ads served by Google; none are shown yet. Advertisers and ad networks have no influence over our sources, formulas, default values or results, and we don't accept payment to feature or rank anything.

7AI use

AI tools help us write code and first drafts. They are never the source of a rate: every figure is confirmed on its official page, and every formula must pass its hand-worked tests before release.

8Reporting a mistake

If a result looks wrong, email hello@smbcalc.com (or see Contact) with the calculator's link (the "Copy link" button includes your numbers), what you expected and, if you can, the source. We check every report. If we were wrong, we fix it, add it to the log below and reply to let you know.

9Corrections and updates log