Convertible Notes: Key Terms, Risks And What UK Startups Should Know

If you’re building a UK startup, you’ve probably had the same conversation more than once: you need funding to grow, but it feels too early (or too messy) to put a firm valuation on the business.

That’s exactly where convertible notes tend to come into the picture. They’re commonly used as “bridge” funding tools for early-stage startups because they can be simpler than a full priced equity round and let you defer the valuation discussion until later.

However, UK founders should know that a lot of online guidance is US-led. In the UK, it’s also common to use other convertible instruments (such as an advance subscription agreement (ASA)) depending on the facts, the tax position, and investor expectations. Either way, you’re signing a legally binding investment instrument that can materially affect your cap table, future fundraising, and your relationship with investors.

Below, we’ll break down how convertible notes work, the key terms you’ll see in practice, the biggest risks for founders, and what you can do to set the deal up properly from day one.

What Are Convertible Notes (And Why Do Startups Use Them)?

A convertible note is typically a loan that can convert into shares in your company at a later date, usually when you raise your next priced equity round.

In other words, an investor gives your startup money now. Instead of receiving shares immediately (at a valuation you need to negotiate today), the investor receives a debt instrument that:

• Accrues interest like a loan (often, interest is added to the amount that converts rather than paid in cash)
• Has a maturity date (a date when the note is due, unless converted/extended)
• Converts to equity if/when a triggering event occurs (most commonly, a “qualified financing” round)

Startups use convertible notes because they can be:

• Quicker to negotiate than a full priced round in the right circumstances (because you may not need to settle a full valuation and investor rights suite upfront)
• Lower cost than a priced round in some cases (but still involves legal work, and costs can increase quickly if terms are negotiated heavily or there are multiple investors)
• Flexible when you’re pre-revenue or still validating product-market fit
• Helpful for deferring valuation (though dilution is not avoided - it’s postponed and depends on the final conversion terms)

That said, a convertible note isn’t “free money” and it isn’t automatically better than equity. It’s a tool - and it can cause real damage if it’s used at the wrong time, on unrealistic assumptions, or drafted poorly for a UK company.

Before you take investment in any form, it’s also worth checking your internal documents are solid. For example, if you have multiple founders, a properly drafted Founders Agreement can help avoid disputes about ownership, decision-making, and what happens if someone leaves mid-way.

Key Terms In Convertible Notes You Need To Understand

Convertible notes are often presented as “standard”, but the terms can vary a lot - and small wording changes can have big consequences.

Here are the key terms you’ll almost always see in a convertible note (and what they mean in plain English).

1. Principal Amount

This is the amount invested (the “loan” amount). For example, an investor subscribes £100,000 under the convertible note.

2. Interest Rate

Convertible notes typically accrue interest over time. The commercial reality is that early-stage startups rarely want (or are able) to pay interest in cash, so the note often provides that interest will:

• accrue and be paid at maturity (less common), or
• accrue and convert into shares along with the principal on conversion (more common).

Even where it converts, interest increases the amount converting - which can mean more dilution for founders than you expected if the note runs for a long time.

3. Valuation Cap

A valuation cap sets the maximum valuation at which the note will convert into equity.

Why it matters: the cap is effectively the investor’s reward for investing early. If your next round is priced at a higher valuation than the cap, the noteholder converts as if the company were valued at the lower capped valuation - meaning they receive more shares for their money.

Founders sometimes focus only on the headline amount raised and forget that the cap is where dilution is often effectively set.

4. Discount Rate

A discount gives the noteholder a percentage reduction on the share price in the next round (e.g. a 20% discount means they convert at 80% of the price paid by new investors).

Some notes include both a valuation cap and a discount, and then apply whichever gives the investor the better outcome. That can be fine - but you need to understand what you’re agreeing to and model the dilution.

5. Maturity Date

This is the date the note is contractually due if it hasn’t converted by then.

In practice, when the maturity date arrives, a few things can happen (depending on the drafting and what the parties agree):

• you repay the note (often not realistic for an early-stage startup),
• you negotiate an extension (often with amended terms),
• the note converts under a “maturity conversion” mechanism (if included), or
• the investor may have leverage to demand repayment or renegotiate from a stronger position.

This is why maturity dates should never be treated as “just a formality”. They can become a pressure point at exactly the wrong time.

6. Conversion Events (Including “Qualified Financing”)

Convertible notes usually convert when you raise your next significant equity round, often defined as a qualified financing (for example, a round where the company raises at least £X from new investors).

That definition matters. If the threshold is too high, you might raise a smaller round that doesn’t trigger conversion - leaving you with ongoing debt and uncertainty.

You should also be clear on whether conversion is automatic or optional, and whether any shareholder/investor consents are needed to issue the shares on conversion (which can depend on your Articles of Association and any shareholder arrangements).

7. Repayment And Default

Even though the commercial expectation is conversion, a convertible note is still debt. That means the document may include default provisions (e.g. insolvency events, breach of obligations) and consequences, including potential acceleration of repayment obligations.

This is one reason you should align your convertible note terms with your broader fundraising documents and governance. For example, a well-structured Term Sheet early on can help keep later negotiations consistent and avoid surprises when you move to a priced round.

Convertible Notes Vs Equity: What’s The Real Trade-Off?

Founders often ask whether convertible notes are “better” than selling equity now. The more useful question is: what are you optimising for?

When Convertible Notes Can Make Sense

• Early stage / pre-valuation: you’re still proving traction, and pricing the company today could undervalue it.
• You need speed: you need capital to hit a milestone (product build, hiring, go-to-market) quickly.
• You expect a priced round soon: a note is often intended as a bridge to a seed round.
• You want narrower negotiations now: you may be able to focus on the economic conversion terms first, then finalise the full priced-round documents later.

When Equity May Be Cleaner

• You already have a clear valuation basis: strong revenue, strong pipeline, or comparable deals.
• You don’t want debt risk on the balance sheet: notes add complexity and can create leverage at maturity.
• You want certainty on dilution now: with notes, dilution is deferred and can stack up across multiple instruments.

Also remember: convertible notes can impact later rounds in ways that aren’t obvious upfront. For instance, if you raise multiple notes (or a note plus other convertible instruments), you can create a “conversion overhang” that complicates your seed round maths and negotiation dynamics.

It’s also worth thinking about how a note interacts with your existing shareholder arrangements. If you already have investors or co-founders, a properly drafted Shareholders Agreement can be crucial to make sure the company can actually issue shares on conversion, and that any consent rights and pre-emption rules are dealt with correctly.

Common Risks And Pitfalls For UK Founders Using Convertible Notes

Convertible notes can be founder-friendly, but they’re not risk-free. Here are the issues we see most often when startups move quickly and don’t fully pressure-test the terms.

1. “Hidden” Dilution (Especially When Notes Stack)

One convertible note can be manageable. But startups often raise a second note, then a third, sometimes each with different caps, discounts, and maturity dates.

By the time you get to your priced round, you might find that a large chunk of the company is already effectively promised away - which can:

• make new investors push for a lower valuation or more aggressive terms,
• reduce founder ownership more than expected, and
• create tension with employees expecting meaningful option equity.

2. Maturity Date Pressure

If the maturity date hits before a priced round happens, founders can feel forced into a financing (or terms) they wouldn’t otherwise accept.

Even if investors are supportive, maturity renegotiations often happen when the company is cash-constrained - which isn’t the strongest negotiating position.

3. Unclear Conversion Mechanics

Conversion provisions need to be crystal clear, including:

• what counts as a qualified financing,
• how the conversion price is calculated (cap vs discount),
• whether interest converts,
• what share class the note converts into (and whether that class exists or must be created), and
• what happens on a sale of the company before conversion (conversion, repayment, or a multiple/return - and how it’s calculated).

If the drafting is vague, disputes can arise when the stakes are highest (your next funding round or an acquisition).

4. Misalignment With Your Existing Corporate Documents

UK startups often use a mix of template articles, early-stage investor arrangements, and informal founder understandings.

That’s normal in the early days - but if your constitutional documents don’t support the note mechanics, you can end up with delays or costly restructuring. For example, the company needs the legal ability to issue the relevant shares on conversion (and to disapply or comply with statutory pre-emption rights where relevant), and your Articles of Association and any shareholder agreements need to be consistent with what the note requires.

If you’re doing any fundraising, it’s smart to check your Articles of Association are fit for purpose and consistent with the deal you’re signing.

5. Tax And Accounting Surprises

Convertible notes can have tax and accounting implications depending on how they’re structured (including whether they’re treated as debt, how interest is handled, whether they’re “quoted”/transferable, and the features attached to conversion).

Sprintlaw can help on the legal structuring and documentation, but we’re not tax advisers or accountants. You should get tailored tax/accounting advice before signing, because “we’ll deal with it later” often turns into “we wish we dealt with it earlier”.

6. Rushing The Legal Documents

Because convertible notes are often marketed as “quick”, founders can be tempted to:

• copy a document from another startup,
• sign something provided by an investor without proper review, or
• use a generic template that doesn’t reflect UK company law, your Articles, or your cap table reality.

That’s a risky move. A note is a legally binding instrument that can affect ownership, control, and future fundraising. Getting it drafted and reviewed properly is part of protecting your company from day one.

What Legal Documents And Housekeeping Should You Have In Place Before Signing A Convertible Note?

Before you sign a convertible note, it’s worth doing a quick “founder readiness” check. You don’t need to be perfect - but you do need to be organised enough that the funding actually helps you, rather than creating a compliance headache.

Make Sure Your Company Structure Is Right

Convertible notes are typically used by limited companies raising investment. If you’re still operating informally, or you haven’t cleaned up early share allocations, it may be time to pause and fix the basics first.

Confirm Your IP Is Owned By The Company

Investors are backing the company’s assets - and for many startups, the core asset is intellectual property (software code, brand, designs, content, processes).

If IP is still personally owned by a founder or contractor, that can spook investors and complicate a note raise. Putting an IP Assignment in place can help ensure the company owns what it needs to grow (and what the investor thinks they’re funding).

Align Founder And Shareholder Expectations

If you have multiple founders or existing shareholders, you want clear rules on decision-making, issuing new shares, and transfer restrictions.

This usually means having the right shareholder documentation in place and ensuring it works alongside any note conversion. A Share Subscription Agreement is typically used for a priced round, but thinking ahead now can prevent your note raise from clashing with how you plan to fundraise later.

Plan For The Next Round

Even if your convertible note is a small bridge, investors will usually expect that the company will raise a priced round later.

So it’s worth asking upfront:

• What funding milestone are you trying to hit before the next round?
• What happens if the next round is delayed?
• Is the valuation cap realistic for where you expect the business to be?
• Will multiple notes create a complicated conversion stack?

Having these conversations early tends to make your next round smoother - and it also reassures investors that you’re building thoughtfully.

Key Takeaways

• Convertible notes are usually loans that convert into equity later, often at your next priced funding round.
• The “headline amount” raised isn’t the whole story - valuation caps, discounts, interest, and maturity dates can significantly affect dilution and negotiating leverage.
• Convertible notes can be a practical way to raise funding early, but they can also create complexity if you raise multiple notes or if conversion terms are unclear.
• Watch out for maturity-date pressure, vague conversion mechanics, and documents that don’t align with your Articles of Association and shareholder arrangements.
• Before signing, make sure your legal foundations are in place (including ownership structure and IP), so the investment strengthens the business rather than creating problems later.
• Because convertible notes are legally binding and can reshape your cap table, it’s worth getting the terms drafted or reviewed properly to fit your company and fundraising plan.

This article is general information only and isn’t legal, tax, accounting or financial advice. If you’d like help drafting or reviewing a convertible note (or planning your fundraising documents end-to-end), you can reach us at 08081347754 or team@sprintlaw.co.uk for a free, no-obligations chat.