A seed fund put money into a startup two years ago and now owns 10% of it. The company is raising its Series A, and the new money will shrink every existing stake. The fund can accept the smaller share or write another check to keep its 10%. Whether it gets that choice at all depends on one clause. This is pro rata rights explained with the numbers: what the right says, how the purchase is calculated and why founders have to plan for it before the next round starts.
The examples below are illustrations, not data about any real company.
What the right says
A pro rata right lets an existing investor buy into a later financing in proportion to what it already owns. It is a right, not an obligation: the investor can use it or let it lapse.
The model term sheet published by the US National Venture Capital Association (NVCA), which many US venture deals start from, puts it under the heading “Right to Participate Pro Rata in Future Rounds.” In the 2020 edition, investors “shall have a pro rata right, based on their percentage equity ownership in the Company (assuming the conversion of all outstanding Preferred Stock into Common Stock and the exercise of all options outstanding under the Company’s stock plans), to participate in subsequent issuances of equity securities.”
Three details in that sentence matter:
- Ownership is fully diluted. The percentage counts preferred stock as if converted and options as if exercised, so the base is larger than the shares actually issued.
- Some issuances are excluded. The model text leaves out the issuances listed in the anti-dilution section of the term sheet and shares sold in an IPO. Option grants to employees, for example, do not trigger the right.
- Unused allocation can pass to others. If one investor does not buy its full share, “the remaining” investors with the right may buy the rest.
The model text puts “[Major]” in brackets before “Investors.” Parties often limit the right to investors above a size threshold that they negotiate, and the template leaves that threshold blank.
Worked numbers: keeping 10%
Take a seed fund that holds 10% of a startup on a fully diluted basis. The company raises an $8 million Series A at a $32 million pre-money valuation, so the post-money valuation is $40 million and the new shares are 20% of the company. To keep the arithmetic visible, there is no option pool increase and no other new security.
| Seed fund does not use its right | Seed fund uses its right | |
|---|---|---|
| Seed fund’s purchase in the Series A | $0 | $800,000 |
| Old stake after dilution | 8.0% | 8.0% |
| Stake from new shares | 0% | 2.0% |
| Ownership after the round | 8.0% | 10.0% |
How it works out:
- Without buying, every existing holder keeps 80% of its previous percentage, because the new money takes 20%. The fund falls from 10% to 8%.
- The pro rata purchase is the fund’s ownership percentage applied to the new issuance: 10% of $8 million, or $800,000.
- That $800,000 buys 2% of a $40 million post-money company. Added to the diluted 8%, the fund is back at 10%.
In a real round the option pool is often topped up at the same time, which dilutes existing holders further. The pro rata calculation still runs off the fully diluted base the agreement defines. Our dilution calculator runs the ownership side of a round with a pool increase.
Who makes room for pro rata
The $800,000 has to come from somewhere. Either the lead investor takes $7.2 million instead of $8 million, or the round grows to $8.8 million. Growing the round means selling more of the company, and that extra dilution falls on everyone who does not buy, including the founders.
The pressure grows with the number of holders. If seed investors with pro rata rights together own 25% of the company, they can claim 25% of the new issuance: $2 million of an $8 million round. A lead that wanted the full $8 million allocation is then negotiating with the founders over who gives way.
Y Combinator’s user guide to the post-money safe makes this point to founders directly. When assembling the priced round, it says, the company has to make room for new investors, existing investors with pro rata rights and perhaps existing investors without formal rights whom the founders still want in. “If you haven’t carefully considered the pro rata right, you may end up taking more dilution than you anticipated.”
Pro rata rights on a SAFE
A SAFE is not stock, so it carries no NVCA-style right by default. Y Combinator’s post-money SAFE, the standard on its documents page, keeps the right out of the SAFE itself and offers it in an optional “Pro Rata Side Letter.”
The timing differs from the original pre-money SAFE. According to YC’s user guide, the old SAFE’s pro rata right applied to the financing after the one in which the SAFE converted: Series B if the SAFE converted in the Series A. The side letter instead applies to the round in which the SAFE converts, usually the Series A. YC says the earlier version was often misread as applying to the conversion round. The guide also says the side letter works only with SAFEs that have a post-money valuation cap, because the investor’s pro rata share is calculated from that cap.
YC tells investors who hold the right to “commit or pass quickly” when the company asks. Its guide says slow responses, sometimes deliberate and sometimes after a round has already closed, are among the biggest problems founders report with pro rata rights, because they hold up allocations and the final cap table. Our guide to the SAFE valuation cap covers how the SAFE converts in the first place.
When the right becomes a duty: pay-to-play
Some financings turn the option into a test. The NVCA model term sheet includes an optional pay-to-play clause: in a later round, which the parties can limit to down rounds, investors must buy their pro rata share of the securities set aside for them. An investor that does not loses some of its rights. The model’s bracketed choices include losing anti-dilution protection, losing the right to participate in future rounds or having its preferred stock converted to common.
The clause is uncommon. Cooley’s Q2 2026 venture financing report says 8.4% of the deals the firm worked on that quarter had pay-to-play provisions, up from 7% in the first quarter. That is one law firm’s deal set, not the whole market. Losing preferred status matters because preferred stock carries the liquidation preference that decides who is paid first in a sale.
Questions to ask before granting or accepting the right
- Which investors get it: everyone in the round, or only those above a “Major Investor” threshold?
- Is ownership measured on a fully diluted basis, and which issuances are excluded?
- For a SAFE, is there a side letter, and does it apply to the round in which the SAFE converts?
- If every holder used its right in full, how much of the next round would that take?
- How long does an investor have to respond once the company announces the round?
- Is there a pay-to-play clause, and what does an investor lose if it does not buy?
