Bridges, extensions, and the Series A crunch

Twenty months after its seed round, Northwind Labs has 7 months of cash. Its revenue is at 70% of what Series A investors want to see. Ada calls the seed lead and asks for a bridge. The seed lead asks one question first: “What will this money get you that you do not have today?” This lesson is about the time between rounds: how long it takes, how many companies get across, and what a bridge costs when the time runs out.

Bridges, extensions, and insider rounds

Carta calls the first equity round in a series the primary round. A bridge round is more money between two primary rounds. These rounds have many names: “Seed+,” “Seed-2,” “Series A-1,” or “A-prime.” The names mean almost the same thing:

• An extension adds money to the last round on the same terms or similar terms.
• A bridge can use new terms, usually on SAFEs, convertible notes, or more preferred stock of the current series.
• An insider round is a round that the current investors fund, with no new lead investor.

A bridge has good reasons and bad reasons. A good reason is “We are near the next milestone and want more time or more money to make the next round stronger.” A bad reason is “We did not get to our milestones, and we cannot raise a new round yet.” The same bridge can look like either one, so new investors ask which it was.

In its report on Q1 2026, Carta gives a direct view: “A bridge is not a strategic financing choice in most cases. It is a continuation of capital while the company earns its way to the next primary round.”

Bridges are frequent

Bridges are not rare events for companies in trouble. A large part of all rounds are bridges.

A secondary summary of Carta data from February 2025 says that approximately 32% to 36% of companies raise bridge money before their next primary round. That is approximately one company in three.

A bridge usually costs more

A bridge buys time, but the price is usually worse than the price of a primary round. Carta reports these facts:

• In the year to Q1 2026, seed bridge valuations decreased 18%, and Series A bridge valuations decreased 16%.
• Bridge terms “typically carry more investor protection than primary rounds.”
• In Q3 2025, the median seed bridge pre-money valuation was $20.7M, and the median Series A bridge pre-money valuation was $45.9M.

The cost to the founders comes later, at the Series A. A bridge on a post-money SAFE takes its part of the company before the Series A money comes in. Then the Series A dilutes all owners, the founders and the bridge investors together.

Worked example · step 1 of 5

Northwind's bridge, share by share

1. 1

   After the seed round

   The seed investors paid $4M at a $20M post-money valuation, or $2.00 a share. Northwind has 10,000,000 shares.

   Founders          7,000,000 shares   70%
   Option pool       1,000,000 shares   10%
   Seed investors    2,000,000 shares   20%
   Total            10,000,000 shares

Show step 2Show all steps

The last step has an important condition. Without the bridge, the company can run out of cash before the Series A, and then the founders have nothing. The bridge is a cost only when you compare it with a Series A that comes at the same price without it.

Now size the bridge yourself. Move the cap below the $20M seed valuation, and then move the Series A price.

Calculator

What a bridge costs the founders

Northwind raised $4M at a $20M post-money valuation. Now it must have more time before its Series A. Size the bridge and see who pays for it.

Bridge amount

$2M

Bridge post-money cap

$30M

The seed post-money valuation was $20M.

Monthly net burn

$150K

Series A pre-money valuation

$60M

Series A raise

$15M

Runway added

13.3 months

$2M ÷ $150K

No bridge

56%

founders after the Series A

With the bridge

52.27%

founders after the Series A

Cost

3.73 points

$2.8M of founder value at the Series A price

After the Series A, no bridge

• Founders
• Option pool
• Seed investors
• Series A investors

After the Series A, with the bridge

• Founders
• Option pool
• Seed investors
• Bridge SAFE
• Series A investors

The $2M bridge gives Northwind 13.3 months of runway at a $150K monthly burn. At the Series A, the SAFE converts at its $30M cap. The bridge investors pay $2.80 a share, and the Series A investors pay $5.60. The bridge investors end with 5.33% of the company.

The founders end with 52.27% instead of 56%.

Work it out

A bridge of $1.5M uses a post-money SAFE with a $25M cap. What part of the company does it own just before the Series A money comes in?

Your answerCheck

The time between rounds

The time between rounds tells you how much runway you must raise. On Carta in Q1 2026, the median times were:

• Seed to Series A: approximately 2.0 years
• Series A to Series B: 2.1 years
• Series B to Series C: 2.4 years.

Carta calls these times “historically elevated.” The seed to Series A time was 420 days, or 1.2 years, in Q4 2021. It increased to 774 days, or 2.1 years, in Q4 2024. In the second half of 2025, it decreased to approximately 1.9 years. AI companies move faster. In PitchBook data for Q1 2026, the median time between rounds was 1.3 years for AI companies and 1.8 years for other companies.

The old advice was to raise every 18 months. For a plan for the worst case, Peter Walker of Carta calls 1,000 days of seed runway “a decent benchmark”:

1,000 days ÷ 30.44 days in a month = 32.85 months
Burn for 1,000 days on $4.5M       = $4,500,000 ÷ 32.85 = $136,986 each month

Fundraising itself also takes months. A common rule from practice is to start to raise when the company has 6 to 9 months of cash or more. The lesson on when and how much to raise turns these numbers into a plan.

Work it out

Northwind raised $4M at seed and wants 1,000 days of runway. What is the most that it can burn each month?

Your answerCheck

The Series A crunch

The graduation rate is the percentage of companies at one stage that raise the next round within a specified time. The Series A crunch is the name for a market in which many seed companies cannot raise a Series A.

Predict first

Of the companies that raised a seed round on Carta in Q1 2022, what percentage raised a Series A within 2 years?

Type a guess before you continue. A guess first, even a wrong one, makes the answer easier to remember.

Your guessSave my guess

Picture it

100 seed companies, two years later

Select a group of companies that raised a seed round in the same quarter. See how many raised a Series A within two years.

Companies with a seed round in

201820192022Recent

• Raised a Series A within 2 years
• Did not, in that time

Graduated

31 of 100

30.6% of the Q1 2018 cohort

Did not, in that time

69

no Series A in 2 years

Of 100 companies with a seed round in Q1 2018, approximately 31 raised a Series A within two years. That was a usual result for the 2018 to 2020 cohorts.

The other companies did not all fail. Some raise a Series A later, some raise a bridge, some sell, and some close.

The rate depends very much on when a company raised its seed round. More data from Carta shows the same pattern:

• Within 1 year: 12.9% of the Q3 2024 cohort, the best quarterly cohort since Q3 2021
• Within 2 years: approximately 14% to 17% for recent cohorts
• Within 3 years: 38% of the Q1 2021 cohort, but only approximately 25% for the 2022 cohorts.

A company that does not graduate did not necessarily fail. Many raise a Series A later, raise a bridge, sell the company, or stay small. Also, recent cohorts did not have their full time yet, so their 3-year values can increase.

What an insider round tells you

An insider round sends a signal, and the signal depends on the facts. If the current investors lead a round at a fair step-up, they show confidence. If they fund a flat round or a down round after missed milestones, outside investors probably said no. New investors will ask why there is no new lead.

The price matters too. A down round is a round at a lower price for each share than the previous round. On Carta, 11.4% of rounds in Q1 2026 were down rounds, against 22.2% in Q1 2024. A down round can start anti-dilution protection for earlier investors. The lesson on down rounds and recaps explains what happens next.

Quiz · question 1 of 6

Test what you learned

Which statement about bridge rounds does the data from 2025 and 2026 support best?

• ABridges are frequent, but they usually cost more and are not guaranteed.
• BA bridge always shows that the company is in trouble.
• CThe price of a bridge is always higher than the price of the previous round.
• DThe current investors must fund a bridge.