How do I add a new co-founder after incorporation?
By SuLe · Updated 1 May 2026
You give the new co-founder shares in one of two ways: allot new shares (which dilutes every existing shareholder and needs an SH01 filed within a month) or transfer existing shares (which dilutes only the seller). Then put them on a vesting schedule, bind them to the shareholders' agreement, and handle the tax and reporting.
Key facts
- Two routes: allot new shares (dilutes everyone) or transfer existing shares (dilutes only the seller).
- An allotment of new shares must be reported to Companies House on an SH01 within one month.
- The new co-founder should be on a vesting schedule and sign a deed of adherence to the existing shareholders' agreement.
- Restricted shares need a section 431 election within 14 days; the issue is an employment-related security reportable to HMRC.
- Share transfers attract 0.5% stamp duty only where the consideration exceeds £1,000.
How do I add a new co-founder after incorporation?
You add them by making them a shareholder — and, usually, a director — with the right documents behind it. The equity itself comes from one of two routes, and everything else (vesting, the shareholders' agreement, tax) is layered on top.
Adding a co-founder is not just a cap table edit. It changes who owns and controls the company, so it needs board approval, the correct share paperwork, and updates to your statutory registers and Companies House filings.
Do it properly at the outset and you avoid the classic problem: an "obvious" co-founder who turns out to have no vesting, no signed agreement, and a chunk of your equity.
Should I allot new shares or transfer existing ones?
This is the first real decision, because it changes who pays for the new co-founder's stake. Allotting new shares creates fresh shares and dilutes everyone proportionally. Transferring existing shares moves them from one holder, so only that person is diluted.
Allotment usually suits a genuine co-founder joining the venture, where all founders accept dilution to bring them in. A transfer suits cases where one founder is effectively giving up part of their stake to the newcomer.
| Allot new shares | Transfer existing shares | |
|---|---|---|
| Who is diluted | Everyone, proportionally | Only the seller |
| Companies House filing | SH01 within one month | None for the transfer itself |
| Main document | Share subscription / board resolution | Stock transfer form (J30) |
| Pre-emption rights | May need to be disapplied or waived | Existing holders' pre-emption may apply |
| Stamp duty | None on new issues | 0.5% if consideration exceeds £1,000 |
What is the process to allot new shares?
The Companies Act 2006 sets the machinery. The directors need authority to allot — check the articles and pass a board resolution, and where existing shareholders have pre-emption rights, those must be disapplied or waived so the new shares can go to the incoming co-founder.
Once allotted, the shares must be entered in the register of members, and form SH01 filed at Companies House within one month of the allotment. The cap table and the next confirmation statement should be updated to match.
For a transfer instead, the steps are lighter: a stock transfer form, updating the register of members, and stamp duty at 0.5% where the price exceeds £1,000 — but there is no SH01, because no new shares are created.
What documents and tax apply to the new co-founder?
The new co-founder should sign into the same framework as the originals. That means a deed of adherence binding them to the existing shareholders' agreement as if they had been a party from the start, plus an IP assignment so their work belongs to the company.
Put them on a vesting schedule — typically four years with a one-year cliff — because an un-vested late co-founder is precisely the risk vesting is designed to remove. For restricted shares, they should sign a section 431 election within 14 days of acquiring them.
On tax, the shares are employment-related securities reportable to HMRC on the annual ERS return by 6 July following the tax year, and shares issued below market value can trigger income tax charges. Check the position before you issue.
Worked example
Priyesh incorporated a foodtech company alone, holding all 1,000,000 ordinary shares of £0.001. A year in, he brings on Dara as co-founder and they agree Dara should hold 30%.
They allot Dara new shares. To leave her with 30%, they issue 428,571 new shares: the total becomes 1,428,571, so Dara's 428,571 is 30% and Priyesh's 1,000,000 is 70%. The board resolves to allot, files an SH01 within one month, and updates the register of members.
Dara signs a deed of adherence to the shareholders' agreement, an IP assignment, and a section 431 election within 14 days. Her shares vest over four years with a one-year cliff — so if she leaves early, the equity comes back rather than staying with someone who did not stay.
Where founders go wrong
Adding a co-founder with no vesting.
A late co-founder with an un-vested 30% is the same trap as a departing founder who keeps everything. Vest their shares.Skipping the deed of adherence.
Without it, the new co-founder is not bound by the leaver, drag and reserved-matters terms everyone else signed up to.Missing the SH01 deadline.
New share allotments must be filed within one month. A late or missing filing leaves the register out of step with reality.Ignoring the tax.
Below-value shares can create income tax charges, and the issue is reportable to HMRC. Check it before issuing, not at year end.
Related questions
What are the two ways to give a new co-founder shares?
Allot new shares, or transfer existing ones. Allotting new shares creates fresh shares and dilutes everyone proportionally; you file an SH01 within a month. Transferring shares moves them from an existing holder and dilutes only that seller, using a stock transfer form. The choice affects who bears the dilution. [More: How do I issue new shares in a UK company?]
Do I need to file anything at Companies House?
For an allotment of new shares, yes — form SH01 must be filed within one month of the allotment, and your registers and next confirmation statement updated. A transfer of existing shares is not filed at Companies House itself, but it must be recorded in the register of members and cap table. [More: What is an SH01 and when must I file it?]
Should the new co-founder's shares vest?
Almost always. A co-founder joining after incorporation should be on a vesting schedule just like the originals — typically four years with a one-year cliff — so their equity is earned over time. Adding an un-vested co-founder recreates exactly the risk vesting exists to prevent. [More: What is founder vesting and how does it work in the UK?]
What does the new co-founder need to sign?
Usually a share subscription or stock transfer, a deed of adherence binding them to the existing shareholders' agreement, an IP assignment, and — for restricted shares — a section 431 election within 14 days. Getting these signed at the point of issue is far easier than chasing them later. [More: What is a deed of adherence?]
Is there tax when adding a co-founder?
There can be. Shares issued to a new founder or director are employment-related securities, reportable to HMRC, and shares given for less than market value can create income tax charges. Transfers over £1,000 attract 0.5% stamp duty. Take advice on the structure before you issue.
Bringing in a co-founder rewrites your ownership and control — and a missed SH01, an un-vested stake, or an unsigned deed of adherence can haunt your next raise. A SuLe solicitor can run the allotment or transfer, set up the vesting, and get the deed of adherence and tax reporting right. Get your founder documents reviewed — book a free consultation and add your co-founder without loose ends.
Keep reading: How many shares should I issue when incorporating a UK startup? · How do I issue new shares in a UK company? · What is an SH01 and when must I file it? · What is a deed of adherence? · What are pre-emption rights — and how are they disapplied? · How should co-founders split equity in a UK startup?
Primary sources: Companies Act 2006 · GOV.UK — Tell HMRC about your employment related securities schemes
