In late 2020, a new tech CFO opened a Substack as a notebook for an audience of one: himself. He was learning the job faster than he could remember it and wanted somewhere to put what he learned before it slipped.
For 18 months, almost nobody read it. His verified readership was his dog and his mother-in-law.
Today, CJ Gustafson runs a finance newsletter that pays him more than his CFO salary ever did.
Nine out of every ten dollars come from sponsors. Some of them pay six figures for a single quarter.
The whole operation traces back to a habit he started for nobody but himself, in a category that had given up on writing this kind of thing down.
An Audience of One
CJ Gustafson had just stepped into his first CFO role at a tech company.
The job was bigger than he was ready for. New problems landed every week without obvious answers.
So he started writing down what he was learning so it wouldn’t slip. He’d later sum it up: “terrified of not remembering the playbook.”
The notes were private at first, but by late 2020 he had a stash worth sharing.
He opened a Substack, named the newsletter Mostly Metrics, and launched a podcast called Run the Numbers alongside it.
The newsletter was where he wrote down what he was figuring out. The podcast was where he talked to people who already had.
The pitch he wrote for himself: a newsletter for current and aspiring CFOs.
The day job stayed.
The early issues read like field notes from someone trying to make sense of his own job, because that’s exactly what they were. Raw, unfiltered, boots on the ground stuff.
Then came the void.
For 18 months, almost nobody saw the work.
Single-digit views per post. The pieces he was proudest of would land with the same audience as the throwaway ones, which is to say nobody.
But he kept writing regardless.
The audience was always partly himself, and a notebook is still a notebook even when nobody else opens it.
He wrote at night. Weekends. Early mornings.
By the time the rest of the internet started noticing, his work problems had a way of becoming Substack drafts within the same week.
How The Notebook Found Its Audience
By mid-2022, something had flipped.
CJ had figured out something subtle about how finance people share writing.
The pieces that traveled were the ones an analyst could forward to their boss to look smart, the ones a CFO could send to their team to make a point, and the ones a VC could pass to a portfolio company to look like a generous mentor.
He started writing for that moment, picking roughly fifteen finance terms he wanted to “own” and building definitive posts around each one.
He said directly: “I want to be the person they forward, because they want to look good.”
The readership went from 500 to 27,000 in the next twelve months.
By 2024, the subscriber base had crossed sixty thousand. The newsletter was going out weekly, and Run the Numbers, the podcast, was publishing twice a week.
Sponsors had started showing up.
CJ had quietly built a system on the side for selling to them, and the early ones had started renewing.
Sponsorships were sold in three-month minimum packages, all at full rate (he never discounted).
He was running two channels, the newsletter and the podcast, so the deals combined both and locked for a quarter at a time.
The first paid sponsors went for $1,000 a post. Within a year they’d climbed to between $5,000 and $10,000 a post.
By 2024, full quarterly packages were crossing $100,000.
His pricing logic was to raise the rate until roughly half the prospects said no, on the framing that there were only two prices in the world: really expensive or free.
Readers had a simpler option: a $15-a-month subscription that unlocked in-depth playbooks for CFOs and access to private company financial benchmarks. About a thousand readers had signed up.
It contributed a small slice of revenue, but the model didn’t depend on it.
By late 2024, total revenue had passed half a million dollars. The newsletter operation could pay him on its own, and in January 2025, he left the CFO job.
The whole thing ran under a holding entity called Mostly Media, with a partnerships lead named Matthew handling sponsor deals.
Behind the Substack page, he’d built a writing system where around seventy drafts sat eighty percent finished at any time so he didn’t feel he was running the gauntlet each time just to get a regular issue out.
He also had a custom GPT trained on every transcript Run the Numbers had produced and was running it as his private research database.
Why Mostly Metrics Was Never a Newsletter
What CJ built is a notebook that happens to have advertisers attached.
The free newsletter is a record of how tech finance really works, which is why it has so much value, because no school teaches what a tech CFO actually does.
Business school covers finance the way it was figured out in the 70s. The CPA exam tests the same old rules.
Neither one touches what a tech CFO has to handle in 2026: SaaS metrics, usage-based revenue, equity in down rounds, raising money when markets crash overnight.
The know-how is out there, but it sits inside the heads of the people doing the job, because those people are too busy doing the job.
CJ decided to write it down though, and working as a CFO for the first four years gave him real material no one could fake.
This is how serious creator businesses get built. The work comes first, the business follows.
If you’ve read earlier pieces in this newsletter, you would have seen a similar pattern.
Aakash Gupta came out of product management. Sahil Bloom came out of private equity. Chris Do came from running a successful design agency.
Knowing the material and writing about it is only part of the way there though.
Standing out and being noticed (for accounting notes of all things) is much harder to do.
Most finance writing reads like a textbook. CJ’s reads like a friend explaining the same stuff at a bar.
He throws in dad jokes.
He mentions his dog.
He calls a bad metric a bad metric instead of dressing it up.
Finance people forwarded his posts because reading his newsletter taught them something valuable, and forwarding his newsletter made them look smart in front of their boss.
His readers are mostly CFOs, VCs, and operators on their way into those jobs.
Those are exactly the people advertisers want to reach.
They pick the software their companies buy. They hire the consultants. They sign the cheques.
That’s what makes Mostly Metrics worth what advertisers pay.
And it all comes back to one bet CJ made: finance is simpler than it looks, and writing it plainly earns you the readers companies are willing to spend big to reach.
How To Write The Playbook Your Industry Keeps Quiet
CJ’s business works because of four specific choices he made. Each one is something you can copy if you have real expertise in your field.
1. Start writing about what you actually learn on the job that surprises you.
The valuable parts of CJ’s writing covered what schools, exams, and industry groups don’t reach.
That gap, between what’s officially taught and what the job actually requires, is your territory.
What surprised you on the job that nobody in your field has written down? Write about that.
2. Keep doing the work while you write about it.
CJ wrote Mostly Metrics for four years while still working as a CFO. His material stayed current because his job kept feeding him problems.
The day job is the moat. Don’t ditch it until the writing genuinely outpaces it (it also gives you added credibility).
3. Write for the forward, not the like.
CJ asked himself who would forward each post and why.
An analyst to their boss, to look smart. A CFO to their team, to make a point. A VC to a portfolio company, to look generous.
He wrote each post for that exact moment.
Map three or four specific reader types and the reason each one would forward your work. Then write to hit those moments.
4. Audit who’s actually reading you.
CJ’s monetization works because his readers control company budgets. Software vendors, consulting firms, and conference organizers pay enterprise prices to reach that audience.
If your readers control the purse strings, attracting high-paying advertising and sponsorship can be a real option.
Your readers determine what kind of monetization will work.
So go find the notebook your industry isn’t keeping. Write it down. The right readers will find you.