What does it take to grow a thriving newsletter with 60,000+ engaged readers all while working full-time as a CFO?
CJ Gustafson, from Mostly Metrics, is on this week’s episode of the Niche Pursuits Podcast to share how he built a highly profitable brand on the side.
In this episode, he delivers a masterclass in newsletter growth, monetization, and the power of niche content.
This is a conversation packed with actionable insights and behind-the-scenes stories, and CJ reveals how he turned a once-slow-growing side project into a high-performing B2B media brand serving over 60,000 subscribers—including CFOs, founders, and business nerds who geek out over financial models and company benchmarks.
Watch the Full Episode
From CFO to Full-Time Creator
CJ Gustafson’s story is a compelling one.
As a tech CFO, he climbed the corporate ladder, gained experience in private equity, and ultimately found his passion in financial analysis and scaling businesses. But in December 2020, he started something on the side—Mostly Metrics, a newsletter that would eventually become his full-time pursuit.
For nearly two years, CJ’s newsletter had just 400 subscribers. He admits it was tough, but he kept writing because he believed in the process. He soon discovered that his unique way of explaining financial metrics and business concepts in plain English was what resonated with people. By simplifying complex topics and infusing humor into his content, he found his audience.
Fast forward to today, and Mostly Metrics has over 62,000 subscribers, a mix of paid and free readers. He recently took the leap and left his CFO role to focus on the newsletter and its related ventures full-time.
Finding the Right Audience
Initially, CJ was writing for “CJ from five years ago”—someone trying to understand financial metrics better. Over time, his audience refined itself:
- 25% are CFOs or work in finance roles
- 20% are entrepreneurs and business leaders looking for better ways to allocate resources and track metrics.
- The rest are investors and business enthusiasts who enjoy learning how companies make money.
One key lesson CJ learned: niche audiences can be extremely valuable.
He questioned whether his target audience was too narrow, but he realized that CFOs control company budgets and make critical financial decisions—making them a highly valuable group for advertisers.
Growth Strategies That Worked
CJ’s newsletter growth didn’t happen overnight. He tested several strategies, some of which worked exceptionally well:
- Owning a Niche on Twitter
- He created a list of 20 finance-related terms and phrases
- Every night, he searched Twitter for those terms and left insightful comments while linking back to his newsletter
- This method helped him grow from 1,000 to 10,000 subscribers
- Guest Posting for Companies
- CJ leveraged his expertise to write guest posts for well-known financial brands like Brex and Mercury
- These partnerships gave him credibility and helped him reach larger audiences
- Starting a Podcast
- His podcast, Run the Numbers, gave him a steady stream of content ideas
- Conversations with CFOs and industry leaders provided new insights that he could turn into newsletter topics
- Leveraging Substack Recommendations
- Being on Substack allowed him to benefit from their recommendation system, which brought in new readers who already followed similar content.
At around 8,000 subscribers, CJ noticed a shift—his newsletter was now gaining 50+ new subscribers daily, purely through word of mouth and organic growth.
Monetization: Building a Business
CJ’s business model evolved over time.
Here’s how he makes money today:
1. Paid Subscriptions
- He turned on paid subscriptions at 11,000 subscribers
- The paid newsletter costs $15/month or $150/year
- Paid content includes playbooks, templates, and deep dives into CFO strategy
2. Sponsorships and Ads
- CJ runs one ad per newsletter, keeping the content clean and premium
- He sells sponsorship packages quarterly, bundling both the newsletter and podcast
- This structured approach helps maintain long-term advertiser relationships
3. Data Reports
- His new Finance Tech Stack 2025 Report is the first of what he expects to be a lucrative data business
- He surveyed over 1,000 CFOs on the tools they use and benchmarked them by company size
4. Exclusive CFO Dinners
- Hosting in-person dinners for 20 CFOs, with a few paid sponsor spots, allows for networking and monetization
- Sponsors value the chance to connect directly with decision-makers
Key Metrics to Track
As a numbers guy, CJ is meticulous about tracking success. Here are the key performance indicators (KPIs) he watches:
- Shares and forwards: The strongest indicator of engagement and organic growth
- Subscriber growth rate: Averaging 1,500–2,000 new subscribers per month
- Engagement signals: More important than likes, he values personal replies and discussions from readers
- Conversion rates for paid subscribers: Helps determine the effectiveness of his free-to-paid content strategy
Lessons for Aspiring Creators
CJ’s journey offers several takeaways for those looking to grow their own audience and monetize content:
- Write about what you know—but make it accessible.
- Find your audience by engaging where they already are.
- Quality content leads to organic growth—don’t rely on hacks.
- Diversify revenue streams, from paid subs to sponsorships and events.
- Create a unique voice and lean into your personality.
Final Thoughts
CJ’s success with Mostly Metrics shows that great content, strategic growth, and audience trust can turn a niche newsletter into a thriving business.
By focusing on quality insights and making financial concepts relatable, he’s built something that CFOs—and anyone interested in business metrics—can’t wait to read.