Anti-Dilution Protection: The Term Sheet Clause That Protects Everyone Except the Founder

 

The name itself is misleading, and that's exactly why so many founders skim past it. "Anti-dilution protection" sounds like something that shields the company, or maybe the founder, from losing equity. It doesn't. It's a clause that protects the investor specifically, at the founder's direct expense and understanding that distinction before signing a term sheet is one of the more important pieces of UK startup funding literacy a first-time founder can have.

What Anti-Dilution Protection Actually Does

Anti-dilution protection is a contractual right that shields existing investors from having their ownership percentage and effective price-per-share devalued if the company later raises money at a lower valuation than a previous round known as a down round. If a company stumbles, misses its milestones, or simply raises during a weak funding market, and the next round prices lower than the last one, anti-dilution provisions kick in to compensate the earlier, protected investor for that value loss.

Here's the part that catches founders off guard: the clause only triggers on a down round. If every subsequent raise happens at the same valuation or higher, the provision sits dormant and never affects the cap table at all. It's specifically a downside protection for investors, activated exactly when the company can least afford to be handing out free equity.

How the Compensation Actually Gets Paid

When anti-dilution triggers, the protected investor doesn't put in more money to buy more shares they receive additional shares, typically issued as a form of bonus or dividend, effectively for free. Those shares have to come from somewhere, and they come from diluting the shareholders who don't have anti-dilution protection: founders, employees holding options, and any other ordinary shareholders. It's a mechanism that quietly redistributes ownership toward the investor and away from the people who built the company, precisely at the moment the company is already under financial pressure.

The Two Flavours, and Why One Almost Never Appears in the UK

There are two standard mechanisms, and the gap between them is enormous. Full ratchet anti-dilution resets the investor's original conversion price entirely to match the new, lower round price regardless of how small that down round is or how many shares it involves. An investor who paid £5 a share can end up repriced to £2 a share even if the down round itself was tiny, which can double their effective stake at the founders' expense. It's the most investor-friendly version of the clause, and precisely because of how punishing it is to founders and other shareholders, full ratchet provisions are rarely seen in UK venture transactions.

Weighted average anti-dilution is the version that actually dominates UK term sheets. Rather than resetting the price outright, it adjusts the investor's conversion price based on both the size of the down round and how many new shares were issued a company raising a modest amount in a down round triggers a much smaller adjustment than one raising a large amount at a steep discount. It's still dilutive to founders, but proportionate to what actually happened, rather than a blunt, disproportionate reset.

The Detail Inside the Detail

Even within weighted average protection, the specific formula matters more than founders often realise. Broad-based weighted average counts all outstanding shares common stock, options, and warrants in the calculation, which produces a gentler adjustment. Narrow-based weighted average counts only the preferred shares, which produces a steeper one. The difference between these two formulas, buried in a schedule most founders never read closely, can meaningfully change how much dilution actually lands on the founder if a down round ever happens.

Why This Clause Deserves More Attention at Signing, Not Less

Founders often treat anti-dilution as boilerplate a standard investor protection that "everyone includes," not worth spending negotiating capital on. That instinct is understandable but risky. The clause sits dormant through every successful funding round, doing nothing and drawing no attention, right up until the one moment it matters most: a down round, when the company is already stressed and the founder has the least leverage to renegotiate anything. Getting the mechanism weighted average rather than full ratchet, broad-based rather than narrow-based right at the term sheet stage costs nothing to negotiate up front and can meaningfully protect a founder's ownership years later, in a scenario nobody wants to plan for but plenty of companies eventually face.

The Bottom Line

Anti-dilution protection isn't a red flag, and it isn't unusual it's standard in institutional funding rounds and a reasonable ask from investors taking on real risk. But its name obscures exactly who it protects, and founders who assume the clause is working in their favour, simply because it sounds protective, are the ones most likely to be surprised by how much equity it can quietly cost them if the company ever has a rough round.

I came across this breakdown while reading a piece in the Entrepreneur Plus Newsletter, which explained the full ratchet versus weighted average distinction more clearly than most term sheet guides manage to.