Undiluted Shares: What They Are And Why They Matter For Startups

When you’re building a UK startup, your equity is more than just a number on a spreadsheet. It’s how you reward founders, attract investors, hire talent, and keep everyone aligned as the business grows.

That’s where undiluted shares come in.

If you’ve ever found yourself asking what undiluted shares are, or why investors keep talking about “fully diluted” ownership, you’re not alone. These terms get thrown around early in fundraising conversations, and misunderstandings can lead to expensive mistakes later (especially when you’re negotiating investment terms).

In this guide, we’ll break down what undiluted shares are, how they differ from diluted and fully diluted ownership, why they matter for UK startups, and the practical steps you can take to manage dilution confidently from day one.

What Are Undiluted Shares?

Undiluted shares generally refer to shares in a company before taking into account future dilution from things like:

• employee share option pools (existing and “top-ups”)
• convertible instruments (such as convertible loan notes and, less commonly in the UK, SAFEs)
• warrants
• future share issues (new investment rounds)

Put simply, an undiluted view of the company shows who owns what right now, based only on the shares currently issued and outstanding.

For example, if your company has issued 1,000 ordinary shares and you hold 600 of them, your undiluted ownership is 60%.

However, if you later create an option pool of 200 shares (or grant options over shares), or raise capital by issuing 500 new shares, your ownership percentage can reduce. That reduction is dilution.

Why The Term “Undiluted” Comes Up So Often

Undiluted shares are often used as a reference point during negotiations. They’re useful because they show the ownership position today.

But in many startup contexts (especially fundraising), looking only at undiluted shares can be misleading, because investors and founders usually need to understand what ownership will look like after certain events occur.

Undiluted vs Diluted vs Fully Diluted: What’s The Difference?

These terms sound similar, but they can mean very different things when you’re talking about ownership percentages.

1) Undiluted Ownership

This is the percentage based on the shares that are currently issued.

• Includes: issued ordinary shares (and any other issued share classes)
• Excludes: options not yet exercised, conversion rights, and planned future issuances

2) Diluted Ownership (In A Practical Sense)

“Diluted” ownership usually refers to your percentage after new shares are issued (for example, after an investment round), meaning your slice of the pie is smaller even if you still hold the same number of shares.

Dilution isn’t necessarily a bad thing. If issuing new shares funds growth, your smaller percentage might be worth more in real terms.

3) Fully Diluted Ownership

Fully diluted typically means the ownership percentage calculated as if certain potential shares were issued. Exactly what counts as “fully diluted” is often definition-driven (for example, as set out in a term sheet or investment documents) and may include:

• shares under an employee option pool (whether only granted, or also ungranted but “allocated/reserved” - depending on the agreed definition)
• shares issuable on conversion of convertible instruments (for example, convertible loan notes and, where used, SAFEs), based on the agreed conversion mechanics
• warrants

This is why investors often focus on “fully diluted” numbers: they want to understand their economic position if (and when) conversion and option rights are exercised in line with the deal terms.

A Quick Example (With Realistic Startup Numbers)

Let’s say:

• Founders have 1,000 shares issued between them
• The company creates an option pool of 200 shares
• An investor invests and receives 500 new shares

Undiluted (before any new issuance): founders own 100% (1,000 / 1,000).

After the investor round (ignoring the option pool for a moment): total issued shares become 1,500, so founders now own 66.67% (1,000 / 1,500).

Fully diluted (treating the option pool as issued too): total would be 1,700, so founders would own 58.82% (1,000 / 1,700).

Same founders, same number of shares - but very different ownership outcomes depending on which lens you use (and, in real deals, how “fully diluted” is defined).

Why Undiluted Shares Matter For UK Startups (Even If Investors Focus On “Fully Diluted”)

If you’re a founder, you might wonder: if fundraising is based on fully diluted ownership, do undiluted shares really matter?

They do - because undiluted shares are still the foundation for how your company is structured, managed, and documented.

They Help You Understand Your Starting Point

Before you negotiate a round, you need a clear “right now” snapshot of ownership. Undiluted shareholdings are often the simplest way to get that snapshot.

This is particularly important if you’re:

• bringing on a co-founder
• reallocating founder equity
• setting up an employee equity plan
• planning your first raise

They’re Central To Founder Relationships

Early-stage startups move fast, but founder fallouts are still one of the biggest risks in the first few years.

Having clarity around who owns what (and on what terms) is a key part of protecting the business. That’s where a well-drafted Shareholders Agreement can be critical, because it can cover not just current ownership, but what happens when someone leaves, wants to sell, or stops contributing.

They Affect Decision-Making And Control

Shares are not only about money - they’re also about control and voting rights.

Depending on the share class structure, shareholders may have different voting rights, dividend rights, and rights on a sale or exit. So, even if your economic ownership is discussed on a fully diluted basis, the legal reality of issued shares still affects governance.

This is also why your Company Constitution (your articles of association) needs to match what you’re trying to achieve as a startup.

They Feed Into Fundraising Negotiations

Even though investors often model on a fully diluted basis, your undiluted cap table is the starting data for:

• pre-money and post-money ownership calculations
• how big the option pool needs to be (and whether it’s created pre- or post-investment)
• how convertible instruments might affect the cap table later

If your undiluted numbers are messy or unclear, negotiations can slow down - and delays during fundraising can be costly.

How To Track Undiluted Shares Properly (Without Getting Lost In The Maths)

Most dilution headaches aren’t caused by a single big decision - they come from not tracking equity consistently as the company evolves.

Here are practical ways to keep your undiluted shares (and your dilution position) under control.

1) Maintain A Clear Cap Table

Your capitalisation table (cap table) is a record of who owns what, including:

• shareholders and share classes
• number of shares held
• issue dates and (sometimes) issue prices
• any options or convertible instruments (so you can model scenarios too)

For many startups, this begins as a spreadsheet. That’s fine - as long as it’s accurate, up to date, and tied back to the company’s formal records (like share certificates, statutory registers, and any Companies House filings where relevant).

2) Don’t Treat The Option Pool As An Afterthought

Option pools are a common dilution trigger.

Founders often agree to “set aside 10% for employees” without realising that:

• investors may require the pool to be created before they invest (so founders absorb the dilution)
• a “top-up” might be required in later rounds
• pool size affects headline valuation negotiations

It’s worth modelling a few scenarios before you lock anything in.

3) Use Vesting To Protect The Startup, Not Just The Numbers

If you issue founder shares upfront and someone leaves early, they may still retain a large undiluted stake - even if they’re no longer helping build the company.

That’s why startups often use vesting arrangements (for founders and/or key team members). A Share vesting agreement can help ensure equity is earned over time, which can also make your cap table more attractive to investors.

4) Make Sure Your Share Issues Are Done Properly

Every time you issue shares, you need to think about:

• director approvals and shareholder authority to allot shares
• pre-emption rights (if they apply)
• updating statutory registers
• filing the correct forms with Companies House within deadlines (for example, an SH01 is generally due within 1 month of an allotment)

This is one of those areas where getting the legal steps right early saves serious headaches later - especially during due diligence for an investment or exit.

Common Startup Scenarios Where Undiluted Shares Can Catch You Out

Undiluted shares often become a problem when founders assume they mean one thing, but a term sheet or investment document uses another approach.

Here are some common scenarios where we see confusion.

Raising Investment On A “Fully Diluted” Basis

An investor might say: “We want 20% of the company.”

That sounds straightforward, but the key question is: 20% of what?

• 20% of the company as-is (undiluted)?
• 20% after an option pool is created?
• 20% on a fully diluted basis (as defined in the documents)?

This is why the definitions in your Term sheet matter. If the drafting is vague, you can end up with unexpected dilution when the legal documents are finalised.

Using SAFEs Or Convertible Instruments

Convertible instruments can be founder-friendly ways to raise money quickly, but they create “shadow dilution” that doesn’t appear in your undiluted share numbers until conversion happens.

In the UK, this is often done with convertible loan notes, and sometimes with a SAFE note (though SAFEs are less standard in the UK and need careful tailoring). You’ll typically have conversion mechanics like valuation caps, discounts, and other negotiated terms. Those mechanics affect the number of shares issued later and therefore the eventual dilution.

Issuing Shares To Advisors Or Early Contributors

It’s common to want to reward early supporters with equity. The risk is doing this informally or without thinking through future rounds.

A small grant can become a big blocker later, particularly if:

• the person becomes uncontactable
• there are no good leaver/bad leaver protections
• future investors want a cleaner cap table

This doesn’t mean you shouldn’t use equity strategically - it just means you should structure it properly from the start.

Assuming “Percentage” Means More Than It Does

Founders sometimes fixate on keeping (say) 60% undiluted ownership.

But your real-world outcome depends on:

• the company’s valuation growth
• the rights attached to different share classes
• how many rounds you raise
• whether the company issues options or convertibles

In other words: your undiluted shares are important, but they’re only one part of the bigger picture.

What Legal Documents Help Manage Dilution And Protect Your Equity Position?

Equity isn’t just a commercial discussion - it’s also a legal framework. If you want clarity around undiluted shares and future dilution, the right documents make a huge difference.

Company Constitution (Articles Of Association)

Your constitution sets the rules for how the company runs, including how shares can be issued or transferred, and what rights attach to different share classes.

For startups, it’s common to update your constitution as you move from “founder-only” to “venture-backed” structure. Your Company Constitution should align with your cap table reality and your growth plans.

Shareholders Agreement

A shareholders agreement can cover the commercial “deal” between shareholders, including:

• reserved matters (decisions requiring shareholder consent)
• transfer restrictions
• drag-along and tag-along rights
• what happens if a founder leaves
• how new shares can be issued and whether pre-emption applies

This is one of the best ways to reduce disputes as your startup grows. It also helps make fundraising smoother because investors usually expect clear governance documents. A tailored Shareholders Agreement is often central to that.

Share Subscription Documents For Investment Rounds

When you raise an equity round, you’ll normally need documents that record:

• how many shares are being issued
• the subscription price
• warranties and disclosures
• conditions precedent (what must happen before completion)

If you’re bringing on investors, a properly drafted Share subscription agreement helps ensure the economics match the negotiated deal - and that everyone agrees on what happens to ownership post-completion.

Vesting Arrangements

Vesting is often used for founders and key hires, so equity is earned over time and can be clawed back in certain exit scenarios. This helps protect the business if someone leaves early and avoids “dead equity”.

A Share vesting agreement is a common way to put this structure in writing.

Be Careful With Templates

Startup equity documents can look deceptively “standard”. But small drafting differences can materially change outcomes - especially around definitions like “fully diluted”, option pool treatment, and conversion mechanics.

It’s worth getting legal advice before signing anything that affects ownership, even if the round feels “simple”.

Key Takeaways

• Undiluted shares reflect current ownership based on shares already issued, without accounting for options, convertibles, or future share issues.
• In startup fundraising, investors often focus on fully diluted ownership, but what’s included in “fully diluted” is usually definition-driven and deal-specific.
• Undiluted shares still matter because they affect your starting point, governance, voting control, and the accuracy of your cap table.
• Common dilution triggers include option pools, investment rounds, and convertible instruments (such as convertible loan notes, and sometimes SAFEs).
• Keeping a clean cap table and properly documenting share issues can save you time and cost in fundraising and due diligence.
• Key documents like a Company Constitution and Shareholders Agreement help manage dilution expectations and reduce disputes as you grow.

Note: This article is general information only and isn’t legal, financial, tax, or accounting advice. Always get advice on your specific cap table and fundraising terms.

If you’d like help setting up your startup’s equity the right way (or sense-checking a raise so you understand what happens to your undiluted shares), you can reach us at 08081347754 or team@sprintlaw.co.uk for a free, no-obligations chat.