Guides
Written by Adrian Simpson, who has been building and running small web and IT businesses for over 20 years.
Twelve guides on invoicing, pricing, tax, and QR codes, written for people running small businesses rather than for accountants. Each one links to the calculator that does the arithmetic.
They exist because the same handful of numbers go wrong for the same reasons, over and over. Somebody adds 30% to their costs and believes they made a 30% margin. Somebody sends an invoice with no due date and wonders why it's still unpaid six weeks later. Somebody prints a thousand flyers with a QR code too small to scan. None of it is complicated once you've seen it, and all of it is expensive the first time.
So these are practical rather than academic. Every one has worked examples with real figures, covers the edge cases that actually come up, and says plainly when the answer depends on where you are. Where a rule varies by country, the guide says so rather than pretending there's one answer.
Invoicing and getting paid
Most invoices that go unpaid aren't disputed. They're missing a detail that stopped somebody processing them, or they landed with terms nobody agreed to. These three cover getting the document right and getting the money in.
- How to Create a Professional Invoice Every field that belongs on an invoice, numbering, credit notes, deposits, and invoicing across borders. Read the guide →
- What Payment Terms Should You Put on an Invoice? Net 7 through Net 90, late fees, deposits, payment methods, and what to do when it still isn't paid. Read the guide →
- Small Business Invoice Checklist A two-minute check before you send, extra checks for new clients, tax-invoice rules, and a monthly review. Read the guide →
Quoting and pricing
The step where the money is won or lost. Price a job on optimistic hours and no amount of careful invoicing recovers it. Start with your own rate, then the difference between margin and markup, then the habits that quietly erode both.
- Quote vs Estimate vs Invoice Three documents, three different promises, plus proformas, purchase orders, and when an estimate runs over. Read the guide →
- How to Write a Professional Price Quote Scope that protects you, tiered options, getting the yes in writing, and what to say when they call it too expensive. Read the guide →
- How to Price Freelance and Contract Work Your real hourly floor, why it sits before tax, retainers, rush and kill fees, and raising your rates. Read the guide →
- Margin vs Markup: The Difference Explained The formulas, what a discount really costs, blended margins on mixed jobs, and what counts as a normal margin. Read the guide →
- Common Pricing Mistakes That Reduce Profit Ten small leaks that never show up as a bad month, and a half-hour exercise to find which ones are yours. Read the guide →
Sales tax and VAT
Two systems that both add a percentage and behave nothing alike. Which one applies, whether the price already includes it, and the order to apply discounts and shipping so the total comes out right.
- Sales Tax vs VAT for Small Businesses How the two systems differ, digital and cross-border sales, the reverse charge, and when to register early. Read the guide →
- How to Calculate Sales Tax on Discounts and Shipping Order of operations, refunds and returns, mixed-rate bundles, gift cards, free shipping, and rounding. Read the guide →
QR codes
Mostly a printing problem rather than a technology one. Size, contrast, and clear space decide whether anyone can scan the thing, and all three are easy to get wrong before a print run.
- How to Use QR Codes on Business Cards Sizing, quiet zones, encoding contact details directly, error correction, and why centred logos work. Read the guide →
- How to Use QR Codes for Menus and Flyers Size by scanning distance, placement, tracking scans without a paid service, and surviving glass and weather. Read the guide →
Where to start
Twelve is a lot to read in order, and you don't need to. Four routes through, depending on what's currently costing you.
New to working for yourself. Read pricing freelance work first, because a rate set too low follows you into every job afterwards. Then margin vs markup, then writing a price quote. That's the sequence from a number in your head to a document a client can accept.
Working, but not getting paid on time. Skip the pricing guides and go to payment terms, then the invoice checklist. Late payment is usually a document problem or a terms problem, and both are fixable in an afternoon.
Busy all year, disappointing numbers. That's common pricing mistakes, which ends with a half-hour exercise on your last ten invoices. It's the fastest way to find out which jobs are actually earning and which are quietly costing you.
Selling products. Margin vs markup and sales tax on discounts and shipping cover most of the arithmetic between the shelf and the till, including refunds, bundles, and gift cards.
The calculators
Every guide links to the tool that does its arithmetic, and each tool page carries its own walkthrough. The profit margin calculator works in both directions, from prices to a margin or from a target margin to a price. The price quote calculator builds a total from your rate, add-ons, discounts, and tax. The sales tax and VAT calculator adds tax or strips it back out of a tax-inclusive figure. The invoice generator turns an accepted quote into a PDF, and the QR code generator makes a static PNG you can print.
All of them run in your browser. Nothing you enter is uploaded or stored anywhere.
These guides are general information, not tax, accounting, legal, or financial advice. Rules differ by country and change over time. For decisions that matter, check with a qualified professional in your area. If you spot something wrong or out of date, tell me and it gets fixed.