"What should I charge?" has no single right answer, but there is a reliable process for getting to a number you can defend, quote confidently, and put on an invoice without a second thought.
Start from your real costs, not a guess
Before thinking about profit, work out what you actually need to earn to cover: your target take-home income, business costs (tools, materials, insurance, software, a vehicle if relevant), and time you cannot bill for directly - quoting, admin, travel, invoicing. New sole traders consistently underestimate this last category, then wonder why a "profitable" day rate does not translate into profit.
Two common pricing models
Hourly/day rate: simplest to calculate and quote, works well when scope is genuinely unpredictable, but penalises you for getting faster and more efficient over time
Fixed price per job: rewards experience and efficiency, gives the client price certainty up front, but requires you to accurately estimate scope before you fully know what you're dealing with
Many tradespeople and freelancers end up using both: an hourly rate as the internal basis for quoting, presented to the client as a fixed price per job. This gives you the predictability of fixed pricing from the client's side while still protecting your actual hourly economics on your side.
Checking your rate against the market
Research what others in your trade and region genuinely charge - not the lowest rate you can find online, which is often outdated or from someone underpricing themselves the same way you might be. Being meaningfully cheaper than everyone else is not a strength; it usually just means leaving money on the table for work you would have won anyway at a fair rate.
Raising your rates without losing clients
Existing clients rarely leave over a reasonable, clearly communicated rate increase - they leave over a rate increase that feels sudden or unexplained. Give notice (a month is standard), state the new rate plainly, and apply it consistently rather than negotiating a different rate with everyone who pushes back.
Once you have settled on rates, the operational side should not cost you any extra effort each time - saved rates for recurring line items (so you are not retyping "callout fee - £45" from memory every time) and automatic subtotal, discount and VAT calculation are exactly what Invoito's recent-items feature and invoice builder are for.