Should I track newsletter growth like MRR?

From the SoleOS answers series — written about our own product space; grounded in published definitions and documented behavior, never invented numbers.

Track newsletter growth with the same rigor as MRR — a defined formula, a consistent cadence, churn included — but never on the same chart or with the same weight. Subscribers are a leading indicator of attention, not a lagging indicator of revenue, and conflating the two leads to false confidence when a list grows but nobody pays. Measure both, label them differently, and only connect them through an explicit conversion rate you check monthly.

Why the instinct to treat them the same exists

If you've set up Stripe or RevenueCat tracking for your products, you already know the comfort of a single clean number that moves: MRR up, good week; MRR down, go find out why. A newsletter list gives you the same dopamine hit — subscriber count up, feels like progress. It's tempting to put both numbers on the same dashboard, same scale, same color-coded "growth rate" treatment.

The problem is that MRR has a built-in accountability mechanism that subscriber count doesn't. MRR drops when someone stops paying. A newsletter subscriber who never opens an email again still counts as a subscriber unless you actively prune your list. You can have 10,000 subscribers and 40% of them haven't opened an email in six months — that list is not growing in any meaningful sense, it's just accumulating dead weight that will eventually hurt your deliverability.

What actually transfers from MRR discipline

A few habits from revenue tracking are genuinely worth applying to a list:

Cohort by acquisition source. Just like you'd want to know whether new MRR came from paid ads or organic search, you want to know whether new subscribers came from a blog post, a lead magnet, a guest appearance, or a referral. Source quality predicts engagement quality far better than total count does.

Track churn, not just gross adds. Most email platforms report unsubscribes, but few founders calculate a churn rate the way they'd calculate logo churn for a SaaS product. If your list grew by 500 last month but 300 unsubscribed, your net growth is 200 — and your gross growth rate was telling you a more flattering story than reality.

Define the metric before you report it. "Subscribers" could mean total contacts, confirmed opt-ins, or active (opened in last 90 days) contacts. Pick one, document it, and don't switch definitions when the number looks bad. This is the same discipline behind having a clear metrics dictionary for your revenue numbers — it should exist for your list too, even if it's just a paragraph in a doc.

What doesn't transfer

Growth rate benchmarks don't apply. A healthy MRR growth rate for a bootstrapped SaaS is a conversation with real anchors — expansion revenue, logo retention, the cost of acquiring a paying customer. There's no equivalent universal benchmark for newsletter growth, because the value of a subscriber varies wildly by niche, by what you're selling them, and by how often you email. A 5% monthly list growth rate means nothing on its own.

Projections behave differently. Revenue projections work because payment events are discrete, dated, and tied to a contract (monthly or annual). Subscriber growth has none of that structure — a single viral post can 10x your signups in a day, then growth flatlines for three months. Trying to fit a smooth projection curve to that is mostly decoration. If you're projecting anything, project your email-to-paying-customer conversion funnel, not the raw subscriber count.

It's not a board-reportable number. If you're running a portfolio of indie products, the question that matters to your own decision-making is "did this list produce customers," not "did this list get bigger." A list of 3,000 engaged subscribers that converts at 2% is worth more to you than a list of 20,000 cold contacts that converts at 0.1%.

The one number worth connecting

The honest link between your newsletter and your revenue is a single ratio: subscribers who became paying customers, divided by total subscribers acquired in that cohort, measured over a fixed window (say, 90 days from signup). Track this per acquisition source if you can — it usually reveals that one channel (often a specific lead magnet or a specific blog topic) converts at 3-5x the rate of the others, and that's the channel worth doubling down on, regardless of which one produces the biggest raw numbers.

This is the kind of connective-tissue metric that's easy to let slip when you're running several products and the newsletter for each one lives in a different tool. If revenue and acquisition data are scattered — Stripe here, RevenueCat there, GA4 somewhere else — it's hard to even ask the "did this list produce customers" question with any confidence. That's part of what SoleOS exists for: pulling Stripe, RevenueCat, GA4, and Search Console data into one view per project so you can eyeball a conversion trend without exporting five CSVs. (Full disclosure: this post was written by the SoleOS team, so take the plug with the appropriate grain of salt.)

If you only run one newsletter feeding one product, a spreadsheet with three columns — month, new subscribers, new paying customers from that cohort — will tell you everything SoleOS would, and you don't need another subscription to maintain it. See SoleOS vs a spreadsheet for an honest breakdown of when the spreadsheet is still the right call.

A practical setup that avoids the trap

1. Keep subscriber count and MRR on separate charts, never the same axis.
2. Report net list growth (adds minus unsubscribes), not gross adds.
3. Tag every subscriber with an acquisition source at signup if your email tool supports it.
4. Calculate subscriber-to-customer conversion quarterly, not monthly — the sample size per month is usually too small to mean anything, a lesson that also applies to how much data you need before a forecast means anything.
5. Prune inactive subscribers (no opens in 90-180 days) before you celebrate a round-number milestone. A smaller, honest list is more useful than a bigger, stale one.

Frequently asked questions

Is list growth a vanity metric?

Not inherently — it's a leading indicator, which is useful, but it's vanity the moment you start reporting it with the same confidence as revenue. The fix isn't to ignore it, it's to be explicit that it's a proxy for attention, not for money, and to always pair it with a conversion number when you're making a decision based on it.

What's a good subscriber-to-customer conversion rate?

There's no universal benchmark worth quoting here — it depends heavily on what you're selling, your price point, and how warm the traffic source is. The useful exercise is tracking your own rate over time by acquisition source and treating any channel that beats your average as worth more investment, rather than comparing yourself to a number you read somewhere.

Should unsubscribes worry me more than slow growth?

Usually yes, especially a rising unsubscribe rate on your regular send (not a one-time list-cleaning prompt). Rising unsubscribes on normal content is a content-fit or frequency problem; slow gross growth is usually a distribution problem. They need different fixes, so don't let one number (net growth) hide which one you actually have.

Can I automate the subscriber-to-customer conversion calculation?

Yes, if your email platform can tag signup source and your payment processor can be queried for matching emails or UTM-tagged checkout links. Most indie founders do this manually once a quarter rather than building real-time automation, since the decision cadence (which channel to invest in next) doesn't need daily updates. If you're already tracking Stripe and RevenueCat together for revenue, the same connector-based approach extends naturally once you're ready to automate it.

Does this change if I have multiple products with separate newsletters?

Yes — keep the lists and conversion rates separate per product rather than summing them into one portfolio-wide subscriber count. A combined number hides which product's list is actually healthy, the same way combined MRR across unrelated apps hides which product is actually growing (see real numbers from a 10-app portfolio for why aggregate numbers without per-project context tend to mislead solo founders).