How long a seed or Series A round lasts, and the time between rounds

Carta's report on private markets for the first quarter of 2026 says: "The typical period between seed and Series A stands at an even two years" [1]. Carta's quarterly reports count the rounds that US companies record on Carta's platform. Two years is a median, the middle value. Half of the companies that raised a Series A in that quarter took longer than two years to get there.

This page gives Carta's figures for each gap between rounds, shows how to work out your own runway, explains what a bridge round is, and applies a simple test of whether the company reaches profit on the money it has. It is part of the guide on building your AI product after you raise.

Runway is the number of months the money lasts

Runway is the number of months a company can keep operating on the cash it has, at its current rate of spending. Burn rate is the net amount of cash that leaves the company each month: what it spends, minus the cash that comes in from customers.

No source opened for this guide defines a formula, so the arithmetic here is this guide's own. Runway in months equals cash in the bank divided by the monthly burn rate. The figures in this table are invented examples.

Cash in the bank	Monthly burn rate	Months of runway
$3,000,000	$100,000	30
$3,000,000	$125,000	24
$3,000,000	$150,000	20
$8,000,000	$250,000	32
$8,000,000	$400,000	20

The table shows what hiring does to runway. A company with $3,000,000 that adds $25,000 a month of cost, which is one hire whose full cost is $300,000 a year or two smaller hires, loses four months of runway. Each hire changes the burn rate for every month that follows.

Two cautions apply to the arithmetic. First, the burn rate moves. An AI product pays a model provider for every request, so the cost of serving users grows as users grow, and the page what an AI feature costs to run shows how to estimate it. Second, revenue lowers the burn rate only when customers pay.

Investors read the burn rate month by month. In a 2022 guide to data rooms, Justine Moore of the venture firm Andreessen Horowitz (a16z) asked founders for a statement that shows "the path from gross revenue through net income (loss) through cash outflow on a monthly basis" [5]. A data room is the shared folder of documents an investor reads before investing. Keep that monthly statement from the first month after the raise, and one of the documents for the next round's data room is ready.

The time between rounds, from Carta's data

Carta publishes the median time between rounds every quarter. These are the figures read for this guide on 26 October 2026.

Gap between rounds	Median time	Quarter	Source
Seed to Series A	2.0 years	Q1 2026	Carta report [1]
Seed to Series A	1.9 years	Q4 2025	Carta post by Peter Walker [2]
Series A to Series B	2.1 years	Q1 2026	Carta report [1]
Series B to Series C	2.4 years	Q1 2026	Carta report [1]

The two seed to Series A figures come from two different quarters, so both can be correct. Carta's report says "The median gap is 2.1 years between Series A and Series B and 2.4 years between Series B and Series C" [1]. It describes these gaps as high by historical standards, and adds that, compared with a year earlier, the gaps at the early stages "are beginning to compress", which means they are getting shorter [1].

Carta's Peter Walker gives the longer view in a post from February 2026, based on 9,843 rounds raised by US startups on Carta. He writes that "in Q4 2025, the median time between Seed and Series A was 1.9 years" [2]. He describes the standard advice as a new round "every 18-24 months", says the medians had been rising since the end of 2021, and names what he sees as the main reasons: "rising interest rates, funding collapsing, and a general risk-off air across VC" [2]. That is, borrowing cost more, less money was available, and venture investors became more careful. He then writes that the medians "are dropping fast" back toward the 18 to 24 month range [2]. Those reasons are his explanation, and his post does not measure them.

Company age is a second measure. Carta's report says the median company raising a Series A in the first quarter of 2026 was 2.8 years old, and that companies raising rounds in 2026 are older than they used to be [1].

How much money and time to raise for

The advice that founders still quote comes from a Y Combinator guide written by Geoff Ralston in January 2016. It says a company that will need another round should raise enough to reach its next "fundable" milestone, the result that makes the next investors willing to invest, which "will usually be 12 to 18 months later" [3]. It suggests answering the question "how much are you raising?" with a number of months: "Simply answer that you are raising for N months (usually 12-18) and will thus need $X" [3]. And it says the ideal is to raise "as much money as you need to reach profitability, so that you'll never have to raise money again" [3].

That guide is ten years old. Carta's medians for 2025 and 2026 run from 1.9 to 2.4 years, which is longer than 12 to 18 months. Reveneau's view is that a founder should plan the spending so the money lasts past the Carta median for the next gap. A plan built exactly on the median is a plan that half of companies would not meet. The milestone itself should be one the next investors care about, and the page what investors expect before the next round covers what that means for an AI company.

The default alive test

In an essay from October 2015, Paul Graham proposed a simple test. He asks: "Assuming their expenses remain constant and their revenue growth is what it has been over the last several months, do they make it to profitability on the money they have left?" [4]. A company that does is "default alive". A company that does not is "default dead". He adds: "Half the founders I talk to don't know whether they're default alive or default dead" [4]. The figure comes from his own conversations with founders.

An invented company shows how the test works. It has $2,000,000 in the bank, costs of $150,000 a month that stay flat, and revenue of $30,000 this month.

• If revenue grows 10% each month, revenue passes costs in month 18, at $151,634 a month, and the company starts that month with $666,341 in the bank. It is default alive.
• If revenue grows 5% each month, the cash runs out in month 20, when revenue is $75,809 a month. It is default dead.

The two cases differ only in the growth rate. Run this test once a month with your own figures. Graham writes that the rest of his conversation with a founder depends on the answer: new plans for a company that is default alive, and how to save one that is default dead [4].

When the money runs short: bridge rounds

Carta defines a primary round as the first equity round in a series, and a bridge round as "any round raised after the first round in a given series" [1]. A bridge round is extra money raised from investors to last until the next primary round. Carta's report says that "many companies simply need to extend the runway" in a market where the number of deals is falling and investors expect more from a company before a primary round [1].

Bridges have a cost. Carta reports that bridge round valuations fell 18% at seed and 16% at Series A in the first quarter of 2026, compared with a year earlier [1]. A valuation is the price investors put on the whole company, so a lower valuation means each dollar raised costs the founders more of their company.

The round counts also fell. Carta reports that seed startups raised $2.7 billion across 381 rounds in the first quarter of 2026, against $2.2 billion across 481 rounds a year earlier, and that Series A companies raised $7.0 billion across 369 rounds, against $6.2 billion across 444 rounds [1]. More money went into fewer rounds.

What the figures cover

Carta's figures describe "equity deals raised in USD by U.S.-based corporations" that are recorded on its platform [1]. A company in another country, or one that raised in another currency, may see different gaps. Carta also warns that historical data may change, because there is often a delay between a deal and the day it is recorded on Carta [1]. Treat each quarter's median as the figure at the time it was published, and check the latest report before you plan.

What this means for an AI product

The plan for the money and the plan for the product are one plan. The months of runway set how much can be built, and the milestone sets what has to be built first. Scope the first version so it reaches the milestone with some months of money left: the guide on how to scope an MVP covers how. Then set the budget lines, which the page engineering budget after a raise works through with public salary and tax figures.

Where Reveneau fits

The number of people on the team is one of the main choices behind the burn rate. Reveneau, an AI software development consultancy with offices in San Francisco and Vancouver, says it uses AI instead of hiring more engineers, so the same build takes a small team, and that it puts that saving into clients' prices. Reveneau says AI writes all of its code and every change must pass an eval suite written from the specification. It says it takes responsibility for the whole project through production and after release. To see how a build would fit your runway, see AI development at Reveneau or contact Reveneau.