Picture the round that needs to happen before anyone can agree what the company is worth. A founder needs cash this quarter; the valuation argument could take months no one has. So instead of pricing the equity now, both sides reach for an instrument that takes the money in today and settles the share count later. Two of those instruments dominate: the SAFE and the convertible note. They look interchangeable from across the table. They are not.
The clean distinction, the one worth holding onto through all the detail below: a SAFE is a right to future equity, and a convertible note is a loan that converts to equity. One is a contract for shares you don't have yet. The other is debt you're owed until it turns into shares. That single difference cascades into everything else - your legal status, your downside, the clock on the deal, and the tax treatment.
Across the table they look identical. On the cap table, one is equity-in-waiting and the other is a creditor.
What is a SAFE?
A SAFE - Simple Agreement for Future Equity - is a contract. Invented at Y Combinator in 2013, it gives the investor the right to receive shares when a defined event happens, usually the next priced equity round. There's no interest, no maturity date, and crucially no obligation on the company to pay the money back. You hand over cash now in exchange for a promise of shares later, priced by reference to whatever the next round sets - adjusted by a cap or discount, which we'll come to.
The appeal is brutal simplicity. A SAFE is short, cheap to paper, and skips the apparatus of a priced round - no new share class, no re-papered shareholders' agreement, no negotiation over a number nobody can defend yet. The cost of that simplicity sits with the investor: a SAFE carries no repayment right and no clock, so if the company never raises a qualifying round, the SAFE can sit unconverted indefinitely.
What is a convertible note?
A convertible note - in the UK, usually a convertible loan note - starts life as debt. The investor lends the company money. The loan accrues interest (often rolled up rather than paid out) and has a maturity date, by which it either converts into shares or, in principle, falls due for repayment. When the next priced round triggers conversion, the outstanding balance - principal plus accrued interest - turns into equity at the agreed terms.
Until that moment, the holder is a creditor, not a shareholder. That status is the whole point. If the company stalls, a note holder ranks ahead of equity and has, at least on paper, a claim to be repaid - though an early-stage company that can't raise often can't repay either, so the protection is more theoretical than first-timers assume. With it comes more paperwork, more negotiation, and interest that quietly enlarges the investor's eventual stake.
What are valuation caps and discounts?
This is the part that actually decides what early money is worth, and it works the same way on both instruments. Going in before a price is set means taking more risk than the investors who follow, so the early cheque gets compensated through one or both of these levers.
- The valuation cap. A ceiling on the company valuation used to convert your money into shares. If the priced round lands above the cap, you still convert at the lower capped number - meaning more shares per pound than the new investors get. The cap is the early investor's reward for conviction before the crowd.
- The discount. A set percentage - commonly 10% to 30% - off the price new investors pay in the priced round. Put in £25,000 on a 20% discount and your money converts as though the shares cost 20% less than the headline round price.
Many instruments carry both and apply whichever gives the investor the better deal. None of this is unique to SAFEs or to notes - it's the shared machinery that lets either one defer the valuation without giving the early money away for free. The numbers in the cap and discount usually matter far more to your return than which of the two instruments you signed.
Where the two genuinely diverge
Strip away the shared plumbing and the real differences are few but consequential. A convertible note is debt: it has interest, a maturity date, and creditor status until conversion. A SAFE is none of those things - no interest, no maturity, no debt. That makes the SAFE lighter and faster, and it makes the note more protective if the wheels come off.
The maturity date is the sharpest practical divergence. A note has a deadline; a SAFE does not. If a noted company hits maturity without a qualifying round, something has to give - an extension, a conversion at a default valuation, or repayment. A SAFE has no such forcing event, which is cleaner for the founder and a quieter risk for the investor, who can be left holding a right that simply never ripens. Interest, meanwhile, slowly grows the note holder's stake; the SAFE holder's entitlement is fixed by the cap and discount alone.
The UK catch: SEIS, EIS and the ASA
Here's where a lot of imported US thinking comes unstuck. For a UK angel, the SEIS and EIS reliefs are often the single biggest reason to be in the deal - and both the standard SAFE and the standard convertible note tend to break them.
The reliefs require a genuine subscription for newly issued shares, with the investor carrying real risk and no right to get the money back. A convertible loan note is, by design, a loan with repayment rights - so at the point you sign it, it generally fails the test. A US-style SAFE, drafted for Delaware rather than Companies House, frequently doesn't fit the UK share-subscription framework either. Lose the timing or the structure and you can lose the relief.
The UK workaround is the Advanced Subscription Agreement (ASA) - the instrument that does the SAFE's job within the rules. An ASA is structured as an irreversible payment for shares to be issued later: no repayment, no interest, no get-out. Drawn up properly, it can preserve SEIS and EIS eligibility where a raw SAFE or note would not. The detail that bites is timing. To keep SEIS in play, HMRC expects the shares to be issued within a short window - in practice no longer than around six months - so an ASA with a distant or open-ended longstop date can quietly forfeit the relief it was meant to protect.
Because the relief turns entirely on how the paperwork is drawn and when the shares are issued, this is a place to check rather than assume. The investor reliefs - 50% income tax relief on up to £200,000 a year under SEIS, 30% on up to £1,000,000 (or £2,000,000 where at least £1,000,000 goes to knowledge-intensive companies) under EIS, each with a three-year minimum hold - are set out in HMRC's guidance: gov.uk venture capital schemes (tax relief for investors). The company-side EIS conditions and the April 2026 changes sit on the company's EIS application guidance.
So what should an investor actually watch?
Not, in the first instance, the choice of instrument. Whether the round is on a SAFE, a note or an ASA matters less than the terms loaded onto it: the valuation cap, the discount, what events trigger conversion, and - in the UK - whether the structure and timing keep SEIS or EIS alive. A generous cap on a note can be a far better deal than a thin one on a SAFE, and a SAFE that quietly kills the tax relief can cost more than the discount ever returns.
One line worth stating plainly, because it's the whole point of how we cover this. None of the above tells you whether to do a given deal, or which instrument to prefer - that's not our job, and it isn't advice. These structures move risk around; they don't remove it, and the underlying companies remain among the most likely investments you can make to lose the entire stake. The tax treatment depends on your circumstances and on rules that shift with each Budget. This piece is general information, not financial or investment advice - take FCA-regulated advice before you commit capital.
Frequently asked questions
What is the difference between a SAFE and a convertible note?
A SAFE is a contract giving the investor the right to shares in a future round, with no interest, no maturity date and no repayment claim. A convertible note is a loan that converts to shares at the next round; it carries interest and a maturity date, and until conversion the investor is a creditor who can, in principle, demand the money back. Both let a round close before a valuation is agreed, using a valuation cap and/or a discount to price the eventual conversion. The headline split is simple: a SAFE is a right to future equity; a convertible note is debt that turns into equity.
What is a valuation cap and a discount?
Both are mechanisms that reward early money for taking early risk. A valuation cap sets a ceiling on the company valuation used to convert the instrument into shares, so if the priced round comes in higher, the early investor still converts at the lower capped figure and gets more shares per pound. A discount converts the early money at a set percentage below the price new investors pay, commonly 10% to 30%. Many instruments include both and apply whichever gives the investor the better price. They appear on SAFEs and convertible notes alike.
Do SAFEs and convertible notes qualify for SEIS or EIS relief?
Usually not at the point you sign them. SEIS and EIS relief require a genuine subscription for newly issued shares with no right to get your money back. A standard convertible note is a loan with repayment rights, so it generally fails the test, and a US-style SAFE often does too. In the UK the common workaround is an Advanced Subscription Agreement, which is structured as an irreversible payment for shares to be issued later, with no repayment and no interest. To preserve SEIS in particular, HMRC expects the shares to be issued within a short window - typically no longer than six months. Always confirm eligibility before relying on it; this is general information, not advice.
Why do founders use a SAFE or convertible note instead of a priced round?
Speed and cost, mainly. Agreeing a valuation early is hard and slow, and a priced equity round needs lawyers, a shareholders' agreement and new share classes. A SAFE or convertible note lets a company take money now and defer the valuation argument to the next round, when there is more information to price on. The trade-off is that the founder is taking cash without fixing what it buys, and the investor is accepting terms today against a price set later.
Which is better for an investor, a SAFE or a convertible note?
Neither is universally better; they shift risk in different ways, and this article does not recommend one over the other. A convertible note gives the investor creditor status, interest and a maturity date, which is more protective if the company stalls. A SAFE is simpler and cheaper but carries no repayment claim and no clock, so an investor can be left holding a right that may never convert if no priced round happens. What matters more than the instrument is the cap, the discount and the conversion triggers. This is general information, not financial advice; take FCA-regulated advice before investing.