From S-1 Deep Dives to the CFO Seat: What IPOs Teach Every Finance Leader, with CJ Gustafson

Most people read an S-1 the way investors do. They look for the numbers that justify a price.

CJ Gustafson reads them as an operator.

CJ Gustafson is a former tech CFO who ran FP&A teams at companies ranging from $10 million to $1 billion in revenue. Today he runs Mostly Media, the company behind the Mostly Metrics newsletter and the Run the Numbers podcast. He has broken down more than 20 IPO filings, from SpaceX and Figma to Chime and Navan. He has also spoken with over 250 CFOs, from Series B companies through to mega-cap public ones.

In this episode of The Growth-Minded CFO, CJ joins Alex and Lauren to cover four things: what CFOs at every stage can learn from companies going public, why selling a business is harder than raising money, how AI is changing the P&L and why every finance leader should be willing to share a point of view.

Writing your way into the room

CJ started Mostly Metrics because he was worried he would forget what he was learning.

Metrics like ARR, CAC payback period and net dollar retention were new at the time. "I'm like, this is so different than what I learned in college," he says. "This is not GAAP revenue and net income."

He also struggled to find resources on these topics that were both informative and enjoyable to read. VCs like Tomasz Tunguz, Jamin Ball and Alex Clayton were writing clearly about SaaS metrics, but almost nobody was writing from the operator's seat. So CJ started "remixing" their approach from the perspective of someone running a company rather than investing in one.

Growth was slow at first. It took him more than two years to reach 400 subscribers, and the first one was his mom. Over the following three years, he grew to 75,000.

Two tactics drove that acceleration. The first was guest posting. CJ offered to write for companies in the finance space. The marketing teams running those blogs often saw them as one more task to get done, but CJ saw them as free distribution to entire customer lists.

The second was what he calls owning the online real estate for 20 ultra-specific terms, such as employee stock options, net dollar retention and LTV to CAC. Every night, he searched for them on X, added an insightful comment to each conversation and linked to an article he had written on the topic.

"I did that for about six months," he says. "You couldn't go online without finding me if you were looking for those terms."

Not everyone was supportive. His employer at the time did not want him building a brand outside the firm. CJ saw it differently: "I think people want to have a relationship with a person, not necessarily a logo of a company."

The two sides parted ways. But investors had been reading his work, and one of them reached out about a CFO opening at a portfolio company. That became his first CFO role, at a vertical software company he helped grow and sell over roughly three years.

"I essentially wrote my way out of one job but promoted myself through my writing."

Read S-1s to learn what good looks like

CJ's interest in IPO filings started early in his career. While consulting at PwC, he was asked to catalog the risk factors in roughly 150 10-Ks and S-1s. The work was tedious, but it taught him to separate legal boilerplate from the risks companies genuinely worry about.

Later, he worked at a company that grew revenue 10 to 20 times over three years and looked to be on the road to an IPO. There, he built the investor relations function and got to know the sell-side banks.

For CFOs who are nowhere near an IPO, he believes the filings offer two big lessons.

The first is metrics. "The first thing is what metrics the company discloses and uses as characters within the overall narrative or plot," CJ says.

That matters even at Series B or C. Most fundraising decks end with a slide showing this year's results, next year's forecast and the margins the company believes it can reach one day. "You have to know what good looks like," CJ says. "And that means you have to look in the public markets where the data is available."

The second is storytelling. The best filings connect several stories into one:

• the market story
• the product story
• how the company turns its product into sales

"Just even hearing the vernacular and words these companies use to describe what they do, I think is incredibly informative."

CJ also believes that at scale, the CFO needs to be able to tell the whole company's story, not just the finance part. "A CFO does become essentially hot-swappable with a CEO at some of these larger firms," he says. If the CEO is out sick, the CFO should be able to step into any investor meeting.

Even at an earlier stage, he says, "you should get the reps in of mentally thinking about it."

Better stories early, better storytellers later

After more than 250 CFO conversations, CJ has noticed a clear pattern.

"The earlier stage CFOs I talk to have better stories. The later stage CFOs I talk to are better storytellers."

One thing does not change at any stage: staying close to the day-to-day rhythm of the business. "It's hard to make any sort of resource allocation decision if you aren't close to the ground truths of what's going on," he says.

Early on, the CFO's job is to build a feedback loop between what is happening and what was forecast. The priority is simple. "The number one job of a CFO is just do not run out of cash," CJ says. As the company grows, there is more and more to protect.

At the top, CFOs have to work at two altitudes, and CJ uses a dolphin to explain it: "A dolphin jumps above the surface to see out further and then it jumps down below to see what's going on at the smallest level."

That means being able to:

• describe a five- or ten-year vision and link it to the product roadmap
• open a spreadsheet with an analyst and talk through deferred revenue for a specific period

Co-host Alex Louisy recognized the same pattern from the CEO seat at Upflow. Founders start with nothing but a story. Then product-market fit arrives, and the business gets so busy that the story is easy to lose. The challenge is to keep telling it through that busy middle stage.

CJ adds one more idea that applies at every stage: your "data diet."

The metrics a CFO relies on will change as the company grows. When you have no FP&A director, you are gathering leading indicators yourself. When you have 50 people in finance and accounting, the task is to make sure they are tracking what tells you whether the business is healthy.

Selling a company is harder than raising money

CJ has done both, and he doesn't think they compare.

The company where CJ was CFO was growing at a healthy pace, but the next stage would take three to five years of heavy investment. That meant changes to the management team and a new product to move from a point solution to a broader platform. Then a larger strategic buyer came in with inbound interest.

"I think the best companies are bought, they're not sold," he says. With a fiduciary duty to everyone on the cap table, the team ran the process.

"When you raise money, you are maybe selling 10% or 20% and the investors are leaning towards what can go right," CJ explains. "When you are selling your entire company, you're selling 100%, and the buyer is leaning towards what can go wrong."

Diligence is exhausting. "Whenever you think you're done, you get another request with another 40 lines."

Timelines also slip. The team expected to close by Thanksgiving, which clashed with a family safari his mom had spent two years planning. CJ went anyway and brought a Starlink with him. He worked half the trip from a tent in Botswana, and at one point a baboon tried to steal the Starlink while he was on a call. The deal closed a week after he got back.

"Deals take on a life of their own."

The experience changed how he sees the CFO role. "You're in charge of investing in your own company, and that's an investor role in my mind," he says. "You're just doing it with one stock in your portfolio."

AI is the loudest new line on the P&L

Right now, CJ is focused on how AI is changing the P&L, and what CFOs will do about rising token costs.

"We've never had a line item enter the P&L as large and as loud as LLM costs," he says. "It's not a bolt-on to the P&L. It has to come from somewhere."

He suggests treating each department as a budget envelope that holds three kinds of cost: people, software and large language models. The goal is to get the best return from the whole envelope.

Two principles are shaping his thinking.

The first is to separate AI costs by where they sit. AI that powers your product belongs in cost of goods sold. AI that makes employees more productive belongs in operating expenses. "Those two costs are measured by different yardsticks," CJ says. Investors will judge gross margin very differently from internal efficiency.

The second is to budget by role, not by average employee. CJ believes employees ramp up over time to what he calls an "efficient frontier" of AI usage. That frontier looks very different for an FP&A analyst than for a staff engineer.

Once the costs are forecast and under control, one question remains: "Was this even a good bet to make in the first place?"

Every finance leader needs a point of view

For CJ, writing has changed everything.

"Writing online is the last true meritocracy where you can literally write yourself into a room," he says.

He doesn't think everyone needs to start a newsletter or a podcast. Consistency is hard, and producing content is now his full-time job. But he does believe everyone should have a point of view.

"Everyone wants to hedge, everyone wants to people-please," he says. "So you end up just with people giving you general life advice, and general life advice generally stinks."

Having a view shows you care enough about something to put yourself out there. CJ believes it also makes it easier for others to share what they think.

In the age of AI, rough edges have become an advantage. "I look for content that's a little rough around the edges now," CJ says. A half-baked idea may not deserve a book, but it can make a good post, and readers know it came from a human.

As for the fear of critics waiting to pounce, CJ has found the opposite problem. "I bet you dollars to donuts that it's gonna be a struggle to get anybody to listen. So just start."

If you're a CFO or finance leader who wants to think beyond your current stage, this conversation shows what the public markets can teach you long before an IPO is on the table. CJ covers reading S-1s for benchmarks and narrative, running a sale process and budgeting for AI across every department. His experience is a useful reminder that the best CFOs stay close to the ground truth, get the reps in on telling the company's story and are willing to share what they think.