Guides

Longer reads on the maths our calculators automate. Each guide explains the reasoning in plain English so you understand the answer, not just receive it — and links to the calculator that does the arithmetic for you.

Margin vs markup: the difference that decides your prices
Two words that sound interchangeable and are routinely confused — with real money at stake. What each one measures, how to convert between them, and the pricing mistakes the confusion causes.
How to set a sustainable freelance day rate
Why dividing an old salary by 260 underprices you, how many days you can genuinely bill in a year, and a step-by-step method for building a rate that survives holidays, admin and quiet months.
Understanding your UK take-home pay in 2026/27
Where your salary actually goes: personal allowance, income tax bands, National Insurance, student loans and pension contributions — including the 60% effective-rate trap above £100,000.
How marketplace fees eat your ecommerce profit
Referral fees, payment fees, fulfilment charges, ad costs and returns stack up faster than most sellers expect. How to work out what a sale really leaves you, and the discounting trap to avoid.
How much waste to allow for building materials
Why every materials estimate needs a waste allowance, sensible percentages for tiles, flooring, paint, bricks and timber, and when to allow more than the rule of thumb.
Bagged concrete vs ready-mix: finding the crossover point
Mixing bags is cheap for small jobs and brutal for big ones. How to compare the true costs — including your labour and consistency — and the volume where ready-mix starts to win.