From side project to UK Ltd company: the 2026 builder's walkthrough

So you spent a weekend with Claude Code, shipped a scrappy little SaaS to Vercel, wired Stripe into a Supabase-backed subscription flow, and this morning you woke up to a payout notification in GBP. Actual money. From a real human. For a product you built yourself.

Congratulations. Now you're staring at your HMRC Self Assessment tab in one browser window and the Companies House registration page in another, wondering whether you're still a sole trader or whether it's time to become a proper grown-up limited company. This guide is the honest, builder-first walkthrough nobody writes because most of the top Google results are formation agents trying to upsell you a GBP 12.99 package with "virtual office included." No waffle, no hype, just the decisions, the numbers, and the 10 steps.

Sole trader vs Ltd: the decision tree

There is no universally correct answer. There are triggers. When one of these fires, you should seriously consider incorporating. When two or more fire, stop procrastinating.

Trigger 1: MRR north of roughly GBP 2,000

As a sole trader, every pound of profit gets taxed at your personal income tax rate plus Class 2 and Class 4 National Insurance. Once your take-home from the side project crosses roughly GBP 24k a year (about GBP 2k MRR), the maths starts to favour a limited company. You pay 19% to 25% corporation tax on company profit, then choose how to extract the money via a low director's salary plus dividends, which are taxed more kindly than salary.

The crossover isn't exact. HMRC rates shift, allowances change, and your personal circumstances matter. But GBP 2k MRR is the rule-of-thumb line where most UK builders realise they're overpaying tax by staying sole trader.

Trigger 2: you're creeping up on the VAT threshold

The VAT registration threshold for 2026 is GBP 90,000 of taxable turnover on a rolling 12-month basis. Not calendar year. Rolling. That means if your last 12 months of Stripe payouts totalled GBP 91k, you must register, whether you like it or not.

Registering for VAT as a sole trader is possible, but if you're going to cross the threshold you might as well incorporate at the same time and get it over with. You only want to do this admin once.

Trigger 3: taking on a co-founder or first hire

Equity is messy without a company. Try splitting a sole trader business with a mate and watch the relationship corrode. With a Ltd, you issue shares, sign a shareholders' agreement, and everyone knows exactly where they stand. If you're about to bring anyone else into the build, incorporate first.

Trigger 4: selling to UK enterprise customers

Procurement teams at real companies will ask for your company number. Some will not contract with sole traders at all. Insurance, supplier onboarding, data processing agreements, all of it gets smoother when you can point to Companies House and say "there we are." If you're trying to close a GBP 5k annual contract with a UK scale-up, the Ltd is basically non-negotiable.

Trigger 5: raising capital or thinking about SEIS/EIS

The UK's Seed Enterprise Investment Scheme and Enterprise Investment Scheme are genuinely world-class tax incentives for investors backing early-stage British companies. They only work if you're a limited company. If angel funding is on your horizon, even 18 months out, start the Ltd clock now. HMRC has minimum trading periods for some reliefs.

Cost reality check

Here's what it actually costs to run a UK Ltd as a solo builder in 2026. No agency markup, no padded fees.

Item	Cost	Notes
Companies House incorporation fee (online)	GBP 100	Increased from GBP 50 on 1 February 2026
Accountant (small Ltd)	GBP 60 to GBP 180 per month	FreeAgent-bundled packages sit at the cheaper end
Business bank account	Free	Mettle, Starling Business, Tide all offer free tiers
Corporation Tax registration	Free	Via HMRC within 3 months of first trade
Confirmation statement	GBP 34 per year	Annual Companies House filing
Your time to set it all up	2 to 4 hours	Spread over a week

That is roughly GBP 900 to GBP 2,300 a year all-in for the compliance stack. If your Ltd is saving you more than that in tax compared with sole trader status, you are winning. For anyone above GBP 2k MRR, it almost always is.

The 10-step incorporation walkthrough

Do these in order. You can realistically complete steps 1 to 5 in an evening and have a live company within 48 hours.

Step 1: check name availability

Go to the Companies House name availability checker at find-and-update.company-information.service.gov.uk. Type your preferred name. If it's taken or too close to an existing name, it'll flag it. A few tips:

• Don't include "Limited" or "Ltd" in the search, it gets appended automatically.
• Avoid "sensitive words" like Royal, Bank, British, Group, unless you want to write a justification letter.
• Check the .co.uk and .com domain at the same time. There's no point incorporating "BuildStack Ltd" if buildstack.co.uk is parked.

Step 2: pick a registered office address

Your registered office is the public address Companies House publishes. A few options:

• Your home address (free, but goes on the public register forever)
• A virtual office (GBP 5 to GBP 15 per month, keeps your home address private)
• An accountant's address (often bundled, sometimes free)

If you're building in public and you value privacy, spend the GBP 10 a month. It's one of the cheapest peace-of-mind purchases you'll ever make.

Step 3: appoint director, shareholders, and PSC

As a solo builder, you are probably all three:

• Director: legally responsible for running the company
• Shareholder: owns the company
• PSC (Person with Significant Control): anyone holding more than 25% of shares, voting rights, or similar

You'll need your date of birth, nationality, occupation, and three pieces of personal verification data (passport number, NI number, mother's maiden name, eye colour, that sort of thing).

Step 4: decide share structure

For a solo bootstrapper, the standard move is 100 ordinary shares at GBP 0.01 nominal value, all held by you. Total paid-up share capital: one pound. Why so small? Because if you later issue more shares to a co-founder or an investor, the maths is clean. Dividing 100 shares is easier than dividing 2.

If you're co-founding, 50/50 is tempting but often bad. One of you will do more. Consider 60/40 with vesting, or issue both sets of shares against a founders' agreement. That's a separate conversation, but don't rush it.

Step 5: register online at GOV.UK

Go to gov.uk/limited-company-formation. Pay the GBP 100 fee. Fill in everything you gathered above. Companies House turnaround is usually 24 hours, sometimes 48. You'll get a certificate of incorporation and your company number by email.

You now legally exist as a corporate entity. Screenshot it, it feels good.

Step 6: get your Unique Taxpayer Reference (UTR)

HMRC will automatically post a letter to your registered office within about 14 days containing your corporation tax UTR. This is a 10-digit number. Guard it, you'll need it every time you interact with HMRC. Do not share it publicly.

Step 7: register for Corporation Tax within 3 months of trading

"Trading" means selling to customers, advertising, renting premises, or earning income. Once you start, you have three months to register with HMRC for Corporation Tax via the Government Gateway. Miss this window and you're looking at a GBP 100 penalty minimum.

You'll be asked to confirm your trading start date and accounting reference date (usually the last day of the month you incorporated, one year on). Don't overthink it, the default is fine.

Step 8: open a business bank account

You cannot legally mix company money with personal money, so this is step one of treating your Ltd like a real entity. For builders, three accounts stand out:

• Mettle (NatWest-owned): free, genuinely good app, integrates with FreeAgent
• Starling Business: free for first year then GBP 7 per month, polished UX
• Tide: free tier available, strong if you need invoicing built in

Most of these approve you in 15 to 30 minutes online. Have your certificate of incorporation and director ID to hand.

Step 9: switch your Stripe payout account

This is the bit builders forget. Log into Stripe, go to Balance settings, and change the payout bank account from your personal account to the new business account. While you're there, update the Stripe account's legal entity from sole trader to limited company. Stripe will ask for your company number and registered office. Five minutes of admin, zero downtime.

If you had customers paying you as a sole trader, consider issuing new Stripe customer records under the Ltd from a clean date, or at least an annotation in your records so your accountant can slice the revenue properly at year end.

Step 10: update your public-facing bits

UK law requires limited companies to show their full legal name, registered office, and company number on:

• Invoices
• Website footer
• Business email signatures
• Terms and conditions
• Order confirmations

Takes about 20 minutes. Do it on the day your UTR lands, then it's done.

The VAT decision (read this carefully)

VAT is the single biggest admin headache for UK SaaS founders. Get it right and it's a rounding error. Get it wrong and you're either handing HMRC free money or facing a nasty bill 18 months from now.

Mandatory: GBP 90,000 rolling turnover

If your 12-month rolling taxable turnover crosses GBP 90k, you must register within 30 days. Taxable turnover for a UK SaaS selling to UK customers means your gross Stripe sales, minus refunds. Business-to-business sales to EU or overseas customers often sit outside this, but check the specific rules for digital services, they get fiddly fast.

Voluntary: when it makes sense

You can register for VAT voluntarily any time. For a builder, this matters because your input VAT (the VAT you pay on your own costs) becomes reclaimable. If you're spending meaningful money on:

• Claude API credits (Anthropic bills GBP + VAT)
• Vercel Pro, Vercel Enterprise, or Vercel AI Gateway usage
• Supabase Pro
• UK-based SaaS tools, design subscriptions, or contractors

Then voluntary registration lets you claw back 20% on those costs. If your monthly tool spend is GBP 500, that's GBP 100 a month back. Worth doing.

The catch: you must charge VAT on your own sales, which either reduces your margin or makes you 20% more expensive to consumer customers. For B2B UK SaaS this is fine because your customers reclaim it themselves. For B2C side projects it hurts.

Flat Rate Scheme for limited-cost traders

The Flat Rate Scheme simplifies VAT: instead of tracking input and output VAT separately, you pay a flat percentage of gross turnover to HMRC. For "limited cost traders" (which most pure-software SaaS businesses are), that rate is 16.5%. Since you charge 20% on sales and pay 16.5% over, you keep the 3.5% spread.

The catch with the Flat Rate Scheme is that you cannot reclaim input VAT on most purchases. If your cost base is mostly Anthropic, Vercel, and Supabase, crunch the numbers carefully. The standard scheme often wins once your tool spend climbs past GBP 1k per month.

HMRC, MTD, and the payroll angle

Three HMRC relationships kick in after incorporation:

Corporation Tax

Filed annually via a CT600 return. Payable 9 months and 1 day after your accounting year end. So if your year ends 31 March 2027, the tax is due 1 January 2028. Don't spend it.

Director's salary plus dividends

The classic UK founder extraction strategy for 2026:

• Pay yourself a director's salary of around GBP 9,100 per year. This uses up your personal allowance and creates a qualifying year for State Pension, without triggering employer NI.
• Take the rest as dividends from company profits after corporation tax.
• Dividends use a separate allowance (currently GBP 500 tax-free) and are taxed at lower rates than salary.

The exact numbers shift each tax year. Your accountant will rebalance this during your year-end review. The headline is: don't pay yourself a big salary. It's the most expensive way to extract money from your Ltd.

PAYE if salary above LEL

The Lower Earnings Limit (LEL) for 2026 is GBP 6,500. If your director's salary crosses that, you must run PAYE. Most accountants include this in their monthly fee. FreeAgent and Xero both do it natively. It's a tick-box, not a project.

Getting money out: salary, dividends, and director's loan

Three ways to move money from the company to you personally:

Salary: run through PAYE, counts as an expense before corporation tax. Simple, predictable, expensive tax-wise.

Dividends: declared from post-tax profits, minuted as a board decision, paid to shareholders. Lower tax rates than salary. The default for founder extraction above the GBP 9,100 salary line.

Director's loan: the company lends you money, you pay it back within 9 months of year end. Useful as a short-term bridge, say, if you've got a personal cashflow gap before a big client payment lands. Two rules keep you safe:

1. Keep the outstanding balance under GBP 10,000 at all times, or it counts as a taxable benefit in kind.
2. Pay it back within 9 months of year end, or the company has to pay 32.5% Section 455 tax on the outstanding balance. You get that tax back when the loan is eventually repaid, but it's a painful cashflow hit in the meantime.

Director's loans are fine in moderation. Treat them as emergency liquidity, not a salary replacement.

Minimum viable record-keeping stack

You don't need enterprise accounting software. You need something that talks to HMRC and doesn't annoy you enough to make you avoid it.

• FreeAgent: free with a Mettle or NatWest business account. Honestly excellent for UK Ltd companies. MTD-compliant out of the box.
• Xero: GBP 15 to GBP 42 per month. More powerful, slight learning curve, better if you scale past one person.
• Crunch or Mazuma: all-in-one accountant plus software bundles from GBP 40 to GBP 140 per month. Hands-off, fine if you hate admin.

Whatever you pick, enable bank feeds day one. Set aside 30 minutes every Friday to categorise the week's transactions. An hour a month saves you two weeks of pain in March.

Also keep: a receipts folder (photos or PDFs), a mileage log if you use your car or EV for business, and a note of every software subscription with the VAT treatment.

The 7-day action plan

• Day 1: Check name on Companies House. Register your domain. Decide on registered office (home, virtual, or accountant).
• Day 2: Incorporate at gov.uk/limited-company-formation. Pay the GBP 100 fee.
• Day 3: Open a Mettle or Starling business account.
• Day 4: Update Stripe to the new entity and point payouts at the business account.
• Day 5: Update website footer, invoices, and email signature with company number.
• Day 6: Sign up to FreeAgent (or your chosen stack). Import opening balances.
• Day 7: Block 30 minutes in your calendar every Friday for bookkeeping. Done.

Your UTR will arrive by post within a fortnight. Register for corporation tax via the Government Gateway when it does. That's it. You're a UK limited company.