A pro rata right entitles an existing investor to participate in a future
financing up to the amount that preserves their ownership percentage. It is a
right to buy, never an obligation: the investor can exercise in full, in
part, or not at all. On priced equity the right is often part of the standard
preferred package (sometimes via statutory preemptive rights); on SAFEs and
notes it usually arrives as a side letter, since the base instruments carry no
such right by default.
The economics cut both ways. For the investor, pro rata is how a fund
concentrates capital into its winners; for the company, every reserved
allocation is a slice of the next round that the new lead cannot have. Leads
price rounds expecting a target ownership; when insider rights consume too
much of the raise, something gives: the round grows, the lead’s target drops,
or someone waives.
The founder’s job is a clean register: who holds pro rata, on what basis it
is calculated (fully diluted is the honest denominator), and what the
aggregate claim represents against the next planned round. Waivers are
negotiable, and far easier to negotiate before a term sheet than across the
table from the lead who just discovered the round is over-allocated.
In Canada
Canadian seed rounds are typically smaller than US ones, and pro rata side letters are handed out just as generously, so the aggregate insider claim collides sooner with the ownership a Series A lead wants. That lead is often a US fund expecting its usual target stake, and discovering an over-allocated round mid-negotiation is a bad way to meet it. On a SAFE stack the right usually lives in side letters rather than in the instrument itself, so the register is easy to lose track of. Insiders exercising, including the government-backed funds present in many Canadian syndicates, remains one of the cleanest signals a new lead reads: the people with the most information are buying again.
Run the numbers
An investor holds 10% of the company on a fully diluted basis. The Series A issues 2,000,000 new shares. Pro rata entitles the investor to purchase 10% of the new issuance, 200,000 shares, at the round price. Buying them keeps the investor at 10% after the round; declining lets the stake dilute to 10% × (old share count / new share count), the normal arithmetic of new issuance, assuming those 2,000,000 shares are the only new issuance. Maintaining 10% also means covering the round's option-pool top-up: buying 10% of the priced shares alone leaves the investor short, because the new pool dilutes them just as it dilutes the founders.
