Business Guides
The rules, rates and formulas behind the tools — explained once, properly, with every figure traced to a primary source.
6 guides
How to Write AI Image Prompts
A five-part prompt formula — subject, context, style, composition, lighting — with worked prompts for product photos, blog heroes and social posts.
Read the guide →2026 Small-Business Rates Reference
IRS mileage, USPS DIM divisors, NMFC classes, FLSA overtime rules and Google Ads budget caps — every 2026 figure small businesses quote, in one sourced table.
Read the guide →Overtime for Tipped Employees: The $5.76 Rule
Tipped overtime is paid on the full minimum wage, not the $2.13 cash wage: $7.25 × 1.5 − $5.12 tip credit = $5.76 an hour. Why the intuitive math is wrong.
Read the guide →2026 Standard Mileage Rate Guide
The IRS business mileage rate changed mid-2026: 72.5¢ through June, 76¢ from July. How to split a claim, plus medical and charitable rates.
Read the guide →How to Charge Late Fees on Invoices
How to set and collect an invoice late fee: the 1.5% monthly convention, why the clause must predate the work, and when statutory interest applies.
Read the guide →Margin vs. Markup: The Complete Guide
Margin divides profit by price, markup divides it by cost. See the conversion table both ways, the formulas, and what confusing the two costs you per sale.
Read the guide →Why these guides exist
Every guide here exists because a calculator alone does not answer the question people actually have. A late-fee calculator gives you $150; it does not tell you whether the clause in your contract makes that fee collectable. A mileage calculator gives you a total; it does not tell you that 2026 has two business rates and a claim spanning July has to be split.
The constants these guides quote — IRS mileage rates, USPS dimensional divisors, NMFTA freight classes, FLSA overtime rules — are the same values our calculators compute with, modelled from primary sources and pinned by unit tests. When a rule changes, the tests fail, the code changes, and the guides change with it.
Each guide follows the same shape. A short answer at the top, because most visitors need one number or one rule and should not have to read 1,500 words to find it. Then the reasoning, the edge cases, and the tables worth quoting elsewhere. Then the calculators that do the arithmetic, and the sources so you can check our work rather than take it on trust.
What you will not find is padding. Where a rule is genuinely simple, the guide is short. Where the honest answer is "this depends on your jurisdiction and you should check", the guide says that instead of inventing a confident number — the mileage and late-fee guides both do this, because both topics have real limits on what a general reference can tell you.
Frequently asked questions
- How are these guides different from the calculators?
- The calculators do arithmetic; the guides explain the rule the arithmetic assumes. A markup calculator will happily convert 50% markup to 33.3% margin, but it cannot tell you that quoting one when you meant the other is the most common pricing mistake in small business. Each guide links to the calculators it feeds, so you can read the rule once and then reuse the tool.
- Where do the figures come from?
- Primary sources only: IRS revenue procedures and notices for mileage and tax figures, the Department of Labor for overtime rules, USPS and NMFTA published tables for shipping. Every guide lists its sources by name at the bottom so you can verify a number rather than trust it. We do not cite other blogs, because that is how an error gets laundered into a fact.
- How often are the guides updated?
- When the underlying rule changes, not on a content calendar. Each guide shows its published and updated dates. The rates the guides quote are read from the same modelled constants our calculators use, and unit tests pin the prose to those constants — so a rate change breaks the build rather than quietly leaving a stale number on the page.
- Is this legal, tax or accounting advice?
- No. These are general references explaining how widely-used rules and formulas work. Late-fee enforceability, statutory interest, overtime classification and deductible mileage all turn on facts specific to your situation and your jurisdiction. For a decision with money or liability attached, check with a professional who can see your actual contract or return.
- Can I quote a table or figure from a guide?
- Yes. The tables are built to be quoted — that is why each one has a caption and a footnote stating its assumptions. Please cite the primary source alongside us where a guide names one, since that source is the authority and we are only the explanation.