Guides
Invoicing guides
Practical answers to the questions that come up when you're actually billing someone — not generic filler.
How to Write an Invoice
What every invoice needs, step by step — from numbering to payment instructions.
Invoice vs. Receipt: What's the Difference?
They look similar but serve different moments in a transaction. Here's how to tell them apart.
Estimate vs. Quote vs. Invoice
They look similar but mean different things — which one is binding, and when to use each.
How to Calculate Sales Tax on an Invoice
The math behind sales tax, VAT, and GST — including multiple rates and compound tax.
Freelance Invoicing Guide
Practical tips for freelancers to get paid faster, including payment terms and deposits.
Construction Invoicing Guide
Milestone billing, retainage, change orders, and work orders for trade and construction jobs.
Medical & Legal Invoicing Guide
Patient vs. insurance billing, superbills, legal retainers, and billing by time increment.
What Is a Commercial Invoice?
Why customs requires one for international shipments, and exactly what it needs to include.
Why these guides exist
Most invoicing advice online is either painfully generic ("always send invoices promptly!") or written to sell a piece of software rather than actually answer the question. These guides are written from the opposite direction: start with a specific, concrete question someone actually has while billing a real client — how do I calculate compound tax, what's the actual difference between an invoice and a receipt, what does customs need on a commercial invoice — and answer it completely, with real formulas and real mistakes to avoid, not filler padded out to hit a word count.
Topics covered so far
- Fundamentals — what every invoice needs and how to number it, the legal difference between an invoice and a receipt (plus where credit notes and debit notes fit in), and how an estimate, a quote, and an invoice each represent a different level of commitment.
- Tax & calculations — the actual arithmetic behind sales tax, VAT, and GST, including multiple rates on one invoice, compound tax, tax-exempt sales, and the difference between how VAT/GST and US-style sales tax work as systems.
- Freelance & independent work — payment terms that get paid faster, deposits, retainers, invoicing clients in another country, and a stage-by-stage plan for what to do when a client goes quiet.
- Trade & construction — milestone billing, a worked retainage calculation, handling change orders without triggering a dispute, and a plain-language primer on liens and lien waivers.
- Medical & legal billing — patient-facing invoices vs. insurance-facing claims, what a superbill actually is, legal fee structures (hourly, flat-fee, contingency), and trust/IOLTA accounting for retainers.
- International trade — what a commercial invoice is, why customs requires one, and Incoterms (EXW, FOB, CIF, DDP) explained.
This list grows over time, and nothing gets added just to hit a publishing schedule — each guide exists because it answers a specific, real question. If there's one you'd like covered that isn't here yet, let us know.
Frequently asked questions
Are these guides free to use?
Yes — every guide on this site is free to read, with no signup or account required, same as the invoice generator itself.
How are these guides different from the invoice-type pages (like the construction or freelance invoice generator)?
The document-type pages (e.g. /construction-invoice-generator/) are focused on that page's own generator — what fields it includes, its templates, and a quick FAQ specific to using the tool for that type. The guides go deeper into the actual subject matter — the mechanics of retainage, the legal difference between an estimate and a quote, how compound tax is calculated — independent of any specific tool. Many guides and their matching document-type page link to each other for exactly this reason.
How often is this list updated?
New guides get added as real, specific questions come up — there's no fixed schedule, and nothing here is padded out just to publish on a schedule. If there's a specific invoicing question you'd like covered, let us know.
Do I need to read a guide before I can create an invoice?
No. The guides answer questions along the way, not as a prerequisite — you can jump straight into the invoice generator with zero prior reading and it'll still produce a correct, professional invoice.
Prefer to just start building?
These guides are meant to answer questions along the way, not to be a prerequisite before you can create an invoice. If you already know what you need, jump straight into the invoice generator, browse the template gallery, or check the FAQ for quick answers about how the tool itself works.
More by document type
For guidance specific to a particular kind of billing, see the dedicated pages for commercial invoices, freelance invoices, receipts, estimates, construction & trade work, and medical, legal & professional billing — each includes a step-by-step walkthrough and common mistakes specific to that document type.