Opyrion Guides
Practical guides for businesses that make and sell things
Costing, stock control, production planning, and the finance side of running a small product business — written as working method, with the formulas and worked examples included.
No sign-up, no gated downloads. Every guide is a complete answer on the page.
Costing and pricing
How to cost a handmade product properly
A four-layer method for working out what a product actually costs to make — materials at the unit you use, labour at a loaded rate, absorbed overhead, and waste — with a full worked example.
14 July 2026 · 7 min read
Margin vs markup: the confusion that quietly costs you money
Margin and markup use the same two numbers and produce very different answers. The formulas, a conversion table, why discounts hurt more than they look, and how to price backwards from a target margin.
21 July 2026 · 5 min read
Setting wholesale and retail prices from one cost base
How to build a price ladder that survives trade discounts: the standard wholesale structure, why you build upward from cost rather than down from retail, and the terms that quietly change what you actually get paid.
28 July 2026 · 6 min read
Stock and purchasing
FIFO or weighted average: choosing an inventory valuation method
The same purchases and the same sales produce different profit figures depending on how you value stock. A worked comparison of FIFO and weighted average, when each suits a small product business, and the rules you cannot ignore.
4 August 2026 · 7 min read
Reorder points and safety stock without the guesswork
The formulas behind when to order and how much: lead time demand, three ways to size safety stock, economic order quantity, and a full worked example showing why lead time variability usually matters more than demand variability.
11 August 2026 · 6 min read
Production
Bills of materials for small workshops: structuring recipes so costs stay true
How to structure a bill of materials that survives price changes and design revisions: single vs multi-level, scrap at the right level, versioning, and a worked multi-level cost roll-up.
18 August 2026 · 6 min read
Production planning for a small workshop: capacity, batches, and the bottleneck
A practical planning method for workshops with a handful of people: calculating real capacity, sizing batches against setup time, finding the constraint that actually sets your output, and a weekly rhythm that fits in an hour.
25 August 2026 · 7 min read
Finance
Why a profitable workshop runs out of cash
Profit and cash are different numbers measuring different things. The cash conversion cycle, why growth consumes cash, how to calculate what each extra euro of revenue costs you to fund, and the 13-week forecast that prevents surprises.
1 September 2026 · 6 min read
What has to be on an invoice in the EU
The particulars an EU VAT invoice must carry, when a simplified invoice is allowed, how numbering and credit notes work, issuing deadlines for cross-border supplies, and what is changing with structured e-invoicing.
2 September 2026 · 6 min read
Reading a P&L for a product business
What each line of a profit and loss statement means when you make and sell things: the cost of goods sold calculation, why gross margin is the vital sign, break-even, and the distortions that make a good month look bad.
2 September 2026 · 6 min read
VAT basics for small product businesses
How output and input VAT work, when registration becomes compulsory, what changes when you sell to another EU country, the One Stop Shop threshold, and why VAT is a cash flow problem before it is a compliance one.
2 September 2026 · 8 min read
About these guides
These guides are written for owner-operators of small product businesses — workshops, studios, small manufacturers, food producers, and specialty retailers. They cover the methods that sit behind day-to-day decisions: what a product really costs, how much stock to hold, when to reorder, and how to read the numbers the business produces. Where a topic touches tax or accounting rules, the guides describe general principles and point you to your accountant for anything that depends on national law.
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