Substack to Kit Paid Newsletter: 12.9% vs 3.5% Fee Math Done Honestly

The fee math, line by line

Substack publishes a flat 10 percent platform fee. That's their take of every paid subscription dollar. Stripe charges 2.9 percent plus 30 cents per successful US card transaction. Add them and a $10 monthly subscription nets the writer $10 - $1.00 - $0.59 = $8.41. That's 84.1 cents on the dollar before tax. The effective platform-plus-processor blended rate is 15.9 percent on small subs, dropping toward 12.9 percent as ticket size rises. I'll use 12.9 percent as the steady-state Substack rate for any subscription above $25 monthly.

Kit's paid-newsletter feature, called Kit Commerce, charges 3.5 percent on each transaction. That fee covers their share plus the underlying Stripe processing — Kit rolled the two into one number for clarity. There is no separate Stripe charge on top. Kit Creator Pro plan is $79 monthly at 5,000 subscribers and adds capabilities Substack doesn't have at any price (sequences, segments, advanced visual automations, custom opt-in forms, integrations with Webflow, Shopify, Teachable, Circle).

The crossover: when does Kit pay for itself?

Kit's monthly fee is fixed. Substack's percentage scales linearly with revenue. The crossover is simple: at what gross MRR does Kit's 79 dollars beat Substack's 9.4 percentage-point penalty?

$79 / 0.094 = $840.43 in monthly revenue. Above $840 MRR, Kit Creator Pro saves money every month. Below that, Substack's free baseline wins. Most paid-newsletter operators with more than 200 paying subs at $5 monthly cross the line.

At $1,500 MRR: you save about $62 per month on Kit, $744 a year.

At $3,000 MRR: $203 monthly, $2,436 a year.

At $5,000 MRR: $391 monthly, $4,692 a year.

At $10,000 MRR: $861 monthly, $10,332 a year.

These numbers are conservative. They ignore Kit's Creator plan at $39 a month for under 1,000 subscribers (which moves the crossover lower) and ignore Stripe volume discounts Kit can negotiate that you don't get on Substack. They also ignore the bigger long-term play: owning your audience instead of being a guest in someone else's house.

What does NOT migrate (and why everyone gets this wrong)

Substack uses Stripe under the hood. Kit uses Stripe under the hood. You'd think subscriber payment methods would just transfer. They don't. Here's why.

Substack's Stripe account is Substack's Stripe account. The customer payment methods belong to Substack as the merchant of record, governed by Substack's Stripe terms. When you leave Substack, you leave the Stripe customer records too. Stripe's Customer Portal does not let merchants export payment-method tokens to a third-party Stripe account. This is a security feature, not a Substack policy decision. PCI-DSS rules forbid token transfer outside the original processor relationship.

Translation: every paying subscriber must re-enter their card on Kit. There is no clever workaround. The re-subscribe email is the entire migration funnel.

Free subscribers ARE different — they can be exported and imported as a clean CSV. The free side of the list moves at near-100 percent retention because the user does nothing.

The re-subscribe email: language that retains 70 percent plus

I've watched ten paid-newsletter migrations off Substack in the past 18 months. The retention spread between best and worst was 41 percent and 84 percent. The variable was the email — same audience size range, same niche cluster, same price points.

Three patterns separate the 80-percent-retention emails from the 40-percent ones.

First: explain the WHY in revenue terms the reader cares about. Not "we're moving to a better platform." Reader does not care. Try: "Substack takes 10 percent of every subscription. That's $X per year of your money paying Substack instead of going to coverage of [the thing they actually subscribed for]. Kit takes 3.5 percent. The difference is what funds [specific upgrade — more posts, deeper research, paid contributors]." Specific dollar numbers and a specific use of the savings hit harder than abstract platform talk.

Second: keep the price the same. Do not raise prices in the same email as the platform switch. The cognitive load of "new platform AND new price" double-prompts churn. Run the platform migration at unchanged price. Raise prices three to six months later if you need to, framed as its own decision.

Third: send the email twice. Day 0 and day 14, with the second send only to people who haven't re-subscribed. Strip the second email of all hedging — it's a one-screen "your subscription expires in 7 days, here's the link" with the same dollar-savings framing. The second send recovers 12 to 18 percent of subscribers who genuinely intended to re-subscribe and forgot. This is the single biggest unforced error operators make.

Avoid: long copy that explains your platform-decision rationale at length. Avoid: deadlines longer than 30 days (people forget). Avoid: any phrase containing the word "exciting." Readers smell it as defensive.

Free subscriber import: clean, automated, near-zero risk

Substack lets you export a CSV of free subscribers from your publication settings. Format: email, name, subscribed_date, status. Kit's importer accepts it directly. About 4 percent of free emails get rejected by Kit as historic bounces or invalid addresses, which is fine — those are emails Substack was retaining as zombie list entries.

Kit will run a list-cleaning pass automatically on import. If you have a sender reputation to protect, request the import be marked as a re-engagement segment for the first month so suppressed subs don't quietly damage your deliverability score.

What Kit gives you that Substack genuinely cannot

Sequences. Substack does not have automation sequences. If you want a 7-email welcome funnel that triggers on signup, Substack cannot do it. Kit does it natively, and on Creator Pro you can branch sequences on subscriber tags or activity.

Tags and segmentation. Substack treats your list as one undifferentiated blob. Kit lets you tag subscribers by source, by interest, by purchase history, then send to subsets. For a paid-newsletter operator running multiple tiers or selling courses on the side, this is the most underrated feature in the migration.

Custom opt-in forms with embedded fields. Substack's signup form is the Substack form. Kit lets you build forms that ask for first name, niche interest, expected use case — feeding the tagging system above.

Integrations. Webflow, Squarespace, Shopify, Teachable, Circle, Memberstack all have first-class Kit integrations. Substack has none of these.

Audience ownership. The list lives in Kit, exportable in clean CSV at any time. Your deliverability is your own problem to solve, but it's also your own asset. On Substack, the list is on Substack's terms.

When you should NOT migrate (and stay on Substack)

Substack Notes is the discovery channel. If a meaningful chunk of your free-subscriber growth is coming from Notes, leaving Substack means giving that up. Kit has no equivalent in-platform discovery surface. Estimate what fraction of your monthly new free subs comes from Substack-internal channels (recommendations, Notes, the explore feed). If it's 30 percent or more, the math gets harder. You may still come out ahead on the fee delta but you're paying for it with growth-rate decay.

Under $300 monthly recurring revenue, Substack's free baseline wins on absolute cost. Kit Creator at $39 a month does not pay for itself until your paid revenue justifies the fixed fee.

If you're under 1,000 free subscribers and not yet earning, Kit's free Newsletter plan IS available — but you'd be running on a platform optimized for creators with paid offers. Substack's free tier is more battle-tested for the prelaunch phase.

The 14-day migration timeline

Day 1: Sign up for Kit Creator Pro. Verify your sending domain (DKIM, SPF, DMARC).

Day 2: Export Substack subscribers as CSV. Import the free side to Kit. Set tags by signup source if Substack provided it. Fire a low-stakes "we have a new home, here's what's coming" send to the free list to warm the new sending IP.

Day 3-4: Build the re-subscribe landing page on Kit. Test the Stripe payment flow end-to-end with a real card. Confirm the post-payment confirmation email fires. Confirm the subscriber lands in the right Kit tag bucket (paid).

Day 5: Send the re-subscribe email to existing paid subs. Same friendly tone as your regular newsletter, not a corporate-feeling announcement. Include the dollar-savings explanation from above.

Day 6-13: Monitor re-subscribe rate. Track in a spreadsheet against your historical churn baseline. Reply personally to anyone who replies to the migration email.

Day 14: Send the second re-subscribe email to non-converters. Make it a one-screen reminder with the link.

Day 30: Cancel Substack publication. Run the final final reminder to anyone still unconverted. Refund pro-rated time on the old platform if your Substack T&Cs require it (in most cases they don't — Substack's terms make subscriptions non-refundable beyond what each paid sub already used).

What I charge to do this for clients

$1,400 flat for a paid-newsletter migration in the 1,500-to-8,000 paid-sub range. That includes Kit setup, DKIM/SPF/DMARC reauthorization, free-list import, paid re-subscribe landing page, two re-subscribe email drafts, and 60 days of deliverability monitoring. Clients recoup the project cost from the platform-fee delta in roughly 90 days at $4,000+ MRR. The productivity gain (Kit's composer is faster) is not in that ROI calculation but adds a few hundred hours back per year for a daily publisher.

The honest case for "stay where you are"

If your paid newsletter is your hobby, your subscribers love the Substack reading experience, and you're under $1,500 MRR — stay. The fee math doesn't justify the migration risk.

If your paid newsletter is your business, you're above $2,500 MRR, and you've ever wished for tagging, automations, or the ability to actually export your list — every month you stay on Substack you're paying about $235 to keep doing so. Run the math with your numbers.