My newsletter started as a hobby. It became a multimillion-dollar business.

• CJ Gustafson worked in finance for tech startups.
• During the pandemic, he started a Substack for CFOs.
• His income from writing and podcasting eclipsed his CFO salary.

This as-told-to essay is based on a conversation with CJ Gustafson, founder of Mostly Metrics and CEO of Mostly Media. It has been edited for length and clarity.

When I walk into a bakery, I’m not debating what kind of treat I want. Instead, I’m thinking about how many muffins they need to sell to keep the lights on. I’ve always been wired that way. I enjoyed writing too, but got into finance because I wanted to make money.

I landed in the startup space, helping scale tech companies. I was the one who budgeted for the rest of the organization, figuring out how much revenue and how many hires we needed to support our operating plan. I learned there were different ways to track a business’s success beyond the gap metrics traditionally used.

There wasn’t much information online framing other ways of measuring success in accessible terms. What did exist was about as interesting as eating glass. I realized this in the winter of 2020, while I was quarantining on Cape Cod. It was cold and dark, so I started writing a Substack purely for fun, mostly on the couch late at night with my dog.

I left my job before monetizing the newsletter

I knew I was onto something when names I recognized from the finance world began subscribing to my newsletter. It pains me to admit, but I had a folder in my email called the Big Baller Folder, and when people who were ahead of me in this industry subscribed or commented, I would save their emails.

My newsletter grew, but it was still small: about 4,000 subscribers. I hadn’t monetized it. Still, the company I was working with gave me an ultimatum: work on the newsletter or stay with them.

Leaving meant abandoning my equity, which was worth about $1 million on paper. I’d just had my first child three months before. And yet, my wife encouraged me to leave. She could see that I was energized by the Substack and that it had the potential to be really big.

I took a CFO role to prove my expertise

Around then, I was offered a chief financial officer (CFO) role through an introduction from my Substack community. The timing was a happy coincidence. I was only 31, which is very young to be a CFO, and I had a lot of imposter syndrome. I had written myself into this room, and I knew I couldn’t mess it up.

It was important to me to succeed in that role to show my credibility in the industry. I helped scale that company 5x within two and a half years. When we sold the company, I made a few million. What was even more valuable was that I had proven myself as a CFO: I could take a company from A to B and facilitate a successful exit.

After the exit, I bet fully on myself

While I was in the CFO role, I continued growing Mostly Metrics and eventually expanded into podcasts. About two and a half years after starting it, I monetized the content. I realized subscriptions weren’t the best avenue, so I focused on ads instead. My readers (and now listeners) are the decision-makers at their companies, so advertisers are willing to pay a premium to reach them.

The last year I was in the CFO role, I made more from Mostly Metrics— about $1.5 million — than I did as a CFO. When we sold the company, I realized I had a choice: I could take another CFO role, where I would make about $500,000 in salary, and about 1% of the company’s value if we sold. That’s a great income, but it’s limited.

Or, I could bet on myself. Success or failure would be all on me, but the potential was uncapped. In February 2025, I made Mostly Media my full-time job. It was the right decision: last year the company made about $3.6 million.

I’m careful to project my creative time

This is the best job I could have, but it’s still a job. It’s not all fun and creativity anymore, so I have to create an environment that helps me show up as my best self. I take runs with my dog to think, and don’t book meetings before 1 p.m. since the morning is for research and writing. I even built a “no machine” in Claude, and use the AI to politely decline invitations.

I hope my financial success will give my three kids the chance to find something that they’re passionate about. You can chase money, or you can bet on yourself and work on something that inspires and energizes you.