When CJ Gustafson launched Mostly Metrics in December 2020, it wasn’t with visions of building a booming B2B media brand. At the time, he was a full-time CFO in the tech world, squeezing in writing between spreadsheets and board meetings. But over time, what began as a small, passion-driven project transformed into a powerhouse newsletter followed by over 60,000 engaged readers—and eventually, his full-time job.
So how did a slow-starting side hustle become one of the most talked-about newsletters in the finance and startup world?
CJ’s journey is one of patience, clarity of voice, and smart strategy—all anchored in a deep understanding of his niche and audience.
The Origin Story: From CFO to Content Creator
CJ’s professional background gave him a front-row seat to the inner workings of company finances. With a career that spanned private equity and tech startups, he was no stranger to financial modeling, benchmarking, and metrics.
But while he thrived in the corporate world, he craved a creative outlet. Enter Mostly Metrics—a newsletter where he broke down complex financial concepts in plain English, often sprinkled with a dose of humor and relatable storytelling. His early readers were small in number, but the feedback was consistent: this was content they didn’t want to miss.
For almost two years, CJ wrote to a subscriber list of under 500. But he kept at it, honing his voice, refining his message, and writing for “CJ from five years ago”—someone who wanted to understand financial metrics better but felt overwhelmed by jargon.
Eventually, his persistence paid off.
Carving Out a Valuable Niche
One of CJ’s smartest decisions was to aim narrow rather than broad. Instead of trying to appeal to everyone with general business advice, he zoomed in on a specific audience:
- 25% of his readers are CFOs or finance professionals
- 20% are entrepreneurs and founders
- The rest? Investors and finance enthusiasts who love digging into how businesses work
This high-value readership became a major asset. CFOs, after all, hold the purse strings of their companies—making them an extremely appealing demographic for advertisers and sponsors.
Growth Without Gimmicks
CJ didn’t rely on viral hacks to build his subscriber base. Instead, he used a combination of targeted engagement, partnerships, and steady content creation:
💬 Owning His Niche on Twitter
He identified 20 key financial terms and every night searched Twitter for them. Then, he left insightful comments and linked back to his newsletter. This grassroots approach took him from 1,000 to 10,000 subscribers.
📝 Guest Posting for Industry Leaders
CJ collaborated with financial startups like Brex and Mercury, contributing guest articles that showcased his expertise and introduced him to new audiences.
🎙️ Launching a Podcast
His podcast Run the Numbers served as both a lead-generation tool and a creative outlet. Each episode sparked new newsletter ideas and strengthened his brand.
🔁 Tapping Substack’s Recommendation Engine
By publishing on Substack, CJ benefitted from cross-promotion with other newsletters in the same space. As his subscriber base hit 8,000, growth took off organically—over 50 new subscribers started rolling in daily, just from word of mouth.
Monetization: More Than Just Paid Subscriptions
While some newsletters rely solely on subscription income, CJ developed a multi-pronged revenue model:
- Paid Subscribers
Once he crossed 11,000 readers, CJ turned on a premium tier—$15/month or $150/year—for deeper content like playbooks and CFO strategy templates. - Sponsorships
Each newsletter includes one premium ad. Sponsors buy quarterly packages that include both the newsletter and podcast, creating long-term relationships and a streamlined workflow. - Data Reports
His Finance Tech Stack 2025 Report was a deep dive based on surveys from over 1,000 CFOs, analyzing the tools they use by company size. This type of data-driven product has become a new and lucrative income stream. - CFO Dinners
Yes, real-life dinners. CJ hosts intimate gatherings of 20 finance professionals, giving sponsors a rare opportunity to connect directly with high-level decision-makers.
Metrics That Matter
As a finance guy, CJ brings the same analytical mindset to his content business. He tracks:
- Shares and forwards, as key indicators of resonance
- Subscriber growth, currently averaging 1,500–2,000 new readers monthly
- Engagement quality, prioritizing replies and discussions over vanity metrics
- Conversion rates from free to paid, constantly testing what drives value
Lessons from CJ’s Playbook
Whether you’re a numbers nerd or just someone looking to start your own newsletter, CJ’s journey offers valuable takeaways:
- Write what you know, but make it engaging and clear.
- Find your niche and speak directly to that audience.
- Engage where your readers already are—don’t wait for them to come to you.
- Focus on long-term value over short-term tricks.
- Diversify your revenue so you’re not dependent on one income stream.
The Bottom Line
CJ Gustafson didn’t chase trends. He focused on value, clarity, and trust—and turned a once-lonely newsletter with 400 subscribers into a thriving, multi-platform brand serving a community of over 60,000 professionals.
His journey is a powerful reminder that even in a crowded digital world, there’s still room for thoughtful, niche content—especially when it’s done with heart, hustle, and a sharp eye for numbers.
