I have just started a business. When do I actually need a website?
You have registered the company, opened the bank account and told your mother. Somewhere on the list, between "get insurance" and "find out what an SIC code is and whether you chose the right one", sits "website". Here is when it actually needs doing, when it genuinely does not, and the one thing about it that is a legal requirement rather than a matter of taste.
Not everyone needs one on day one, and we build them
This is against our interests, so it is presumably true. If you are a tradesperson whose first year of work is coming from people who already know you, a completed Google Business Profile with real photographs and a phone number that gets answered will do more for you in month one than any website. It is free, it takes an afternoon, and it is where "electrician near me" actually goes. Do that first. Do it properly. Then consider whether you have any evenings left.
The same applies if the business is a side project while you are employed elsewhere. Until the thing has legs, spend your evenings on the thing, not on a website about the thing. A website about a thing that does not yet exist is a peculiar object, and visitors can tell.
When you do, which is sooner than you would like
The calculation changes the moment people start checking you out before they commit, and for professional services that moment is roughly immediately. An accountant, a solicitor, a consultant, a mortgage adviser: someone meets you, likes you, and then that evening, in the manner of a person checking whether the restaurant they enjoyed has a hygiene rating, types your company name into Google. What they find is the entire question.
Find nothing and a proportion of them conclude you are very new, very small or not entirely real, and they will not tell you which. Find a Companies House entry and a LinkedIn page and they at least know you exist. Find one page saying who you are, what you do, where you are and how to get hold of you, with a photograph of an actual human, and the meeting is confirmed rather than undermined. That is the whole job of a first website. Not to generate clients. To avoid losing the ones you have already met.
A workable rule: if a client would be faintly embarrassed to admit they hired you without looking you up, you need a website before the first client, not after.
The legal bit, which nobody mentions and everybody gets wrong
If you have formed a limited company, the law has views about your website. The Companies Act 2006 and the trading disclosure regulations beneath it require a company's website to show its registered name, registered number, the part of the UK it is registered in, and its registered office address. Somewhere findable, not buried on a page called "legal stuff" that nobody can locate. The footer is the customary spot, and it is where ours lives. It is a small rule, easily kept, and a brand new company breaking a disclosure requirement in its first week is not the impression anyone was going for. Sole traders are spared this one, though your own name and a contact address are still expected of you.
What the first website should be
Small. Properly small. One page can be enough: who, what, for whom, where, how to get in touch, and one photograph of you taken this year rather than at a wedding in 2019. Add a second page if you have something worth saying at length. Add a third if clients will want prices. Resist, with everything you have, the fourteen-page site with a services dropdown. You do not have fourteen pages of things to say yet, and pretending otherwise produces the sort of copy that reads as though it was extruded.
Two things to avoid. A "coming soon" page, which announces that you started something and have not finished it, and is worse than silence. And a free builder's subdomain, so your business lives at yourname.somebuilder.com like a lodger. Buy the domain. It costs about ten pounds a year and it is the only part of a website you will ever truly own.
The do-it-yourself question
You can build a one-page site on a builder in a weekend, and for plenty of new businesses that is the correct decision. You are trading the weekend, a monthly fee that continues until the heat death of the universe, and a site the platform owns rather than you, in exchange for control and a low up-front cost. If the weekend is genuinely spare and you enjoy this sort of thing, do it. If you would rather spend the weekend on the business, that is what people like us are for. Our smallest site is one page at £125, you see it working before you commit to anything, and the files are yours.
In one line
Before the first professional client, if people will look you up. Whenever you get round to it, if they will not. And either way, the company details go in the footer, because that bit is not a preference.
If you have just incorporated and want to see what a first page could look like, the homepage mock-up is free, with no obligation whatsoever attached.