Anti-Dilution Explained: Full Ratchet vs Weighted Average (and Why the Difference Matters)

By Clarence Tan

1. Introduction

(a) Anti-dilution provisions are one of those terms that founders often skim past during early fundraising. They are rarely the focus of negotiations when valuations are rising and capital is abundant. In practice, however, anti-dilution only becomes visible when something goes wrong.

(b) This typically occurs when a company needs to raise capital at a lower valuation, or when new investors scrutinise existing terms and insist on changes before committing fresh money. By the time anti-dilution becomes a live issue, founders are often under pressure, and the clause no longer feels theoretical.

(c) Understanding the difference between full ratchet and weighted average anti-dilution early can therefore make a meaningful difference when conditions become more challenging.

2. Where Anti-Dilution Clauses Usually Sit

(a) One reason anti-dilution is commonly misunderstood is that it does not always appear in an obvious place. In convertible notes and other convertible instruments, anti-dilution typically sits within the conversion mechanics and operates only when a future equity financing occurs.

(b) In equity rounds, anti-dilution is often not fully set out in the subscription agreement itself. Instead, the subscription agreement may refer to the rights attached to the shares being issued, with the detailed mechanics appearing in the shareholders’ agreement or the company’s constitution.

(c) As a result, founders may approve an equity round without ever reading the clause that ultimately governs how dilution risk is allocated.

3. What Anti-Dilution Is Trying to Do

(a) Conceptually, anti-dilution does not prevent dilution. Dilution is inevitable when new shares are issued.

(b) What anti-dilution does is reallocate the economic impact of a down-round. It determines how much of that impact is borne by existing shareholders, and how much protection is afforded to earlier investors who invested at a higher price.

(c) The key question is therefore not whether dilution occurs, but who absorbs more of it when shares are issued at a lower valuation.

4. Full Ratchet Anti-Dilution

(a) Full ratchet anti-dilution is the most straightforward form of protection. If the company later issues shares at a lower price, the earlier investor’s original purchase price is effectively reset to that new lower price.

(b) The size of the down-round does not matter. Even a small issuance at a lower price can trigger a full reset.

(c) From an investor’s perspective, full ratchet offers certainty. From a founder’s perspective, it is the most severe outcome. The adjustment can result in a significant increase in the number of shares issued to earlier investors, even if the down-round itself is modest.

(d) Full ratchet shifts almost all of the downside valuation risk onto founders and ordinary shareholders. It is clean and easy to understand, but its economic impact can be disproportionate.

5. Weighted Average Anti-Dilution

(a) Weighted average anti-dilution takes a more balanced approach. Instead of fully resetting the earlier price to the new lower price, it adjusts the price based on both the lower price and the number of shares issued in the down-round.

(b) In simple terms, the more shares issued at the lower price, the greater the adjustment. If only a small number of shares are issued, the adjustment is correspondingly smaller.

(c) For this reason, weighted average anti-dilution is generally viewed as less punitive to founders than full ratchet.

(d) That said, weighted average protection is not benign. In a meaningful down-round, the adjustment can still materially dilute founders. The difference is one of degree, not principle.

6. A Simple Comparison in a Down-Round

(a) The practical difference between full ratchet and weighted average becomes clear in a down-round scenario. Under a full ratchet, the earlier investor is treated as if they had invested entirely at the new lower price, regardless of how small the down-round may be.

(b) Under a weighted average, the earlier investor’s price moves downward, but only part of the way. The adjustment reflects both the severity and the scale of the down-round.

(c) For founders, this usually means giving up fewer additional shares than under a full ratchet, but still more than they initially expect.

(d) This distinction is often only appreciated when founders see the cap table after the adjustment has been applied.

7. A Note on Broad-Based and Narrow-Based Weighted Average

(a) Not all weighted average formulations are the same. The difference between broad-based and narrow-based weighted average lies in how the existing share base is defined for the adjustment calculation.

(b) Broad-based weighted average takes into account a wider pool of shares, which typically results in a softer adjustment.

(c) Narrow-based weighted average uses a smaller pool, leading to a more aggressive outcome. In economic effect, a narrow-based weighted average can sometimes come closer to a full ratchet than founders expect, even though it is still labelled as weighted average.

8. Why Anti-Dilution Causes Problems in Later Rounds

(a) Anti-dilution provisions often become contentious not just because of their effect on founders, but because of how they interact with future investors.

(b) New investors may be reluctant to invest into a structure where aggressive anti-dilution rights materially distort the cap table or concentrate risk on founders.

(c) In such cases, founders may be asked to renegotiate or waive existing protections, often at a time when they have limited leverage. What was once accepted as “market standard” can quickly become a hurdle to closing the next round.

9. Closing Takeaway

(a) The key issue for founders is not mastering formulas or drafting mechanics, but understanding how anti-dilution protection operates in economic terms and how severe its effect can be in a down-round.

(b) Full ratchet and weighted average anti-dilution allocate downside risk very differently, and that allocation can meaningfully affect ownership, control, and the feasibility of future fundraising.

(c) Anti-dilution is easiest to evaluate when conditions are favourable and hardest to revisit when capital is scarce. Assessing its impact early allows founders to make informed trade-offs, rather than confronting unexpected outcomes under pressure.