Substack Boost Automates Discounts—but Every Offer Needs a Review

Substack Boost automatically surfaces selected conversion and retention offers for paid publications. Publishers can customize the engaged-subscriber email, switch individual documented mechanisms on or off, or disable Boost entirely, but editing rights are not identical across every offer.

That makes Boost a collection of separate commercial interventions, not one campaign with uniform controls. Its conversion email, post-checkout network discount and cancellation incentive address different readers at different moments, so each deserves its own approval decision.

What Boost automates

The official Boost support page says the engaged-subscriber email is designed to reach about 0.1% of a publication’s email list per day and defaults to 20% off for one year; the post-checkout mechanism can discount another Boost-enabled publication by up to 20%, while the pre-cancel mechanism offers an eligible paid subscriber one free month.

The email audience is selected using a score based on engagement metrics and predicted likelihood of converting from free to paid. The post-checkout offer appears after a reader pays for a different publication, while the cancellation incentive appears when an eligible existing subscriber starts cancelling.

These mechanisms can be selected or unselected in the Boost area of publication settings. Once payments are enabled, Boost appears under Growth; a publication-wide control labeled “Enable Substack Boost” provides the master opt-out.

The offer-by-offer control map

• Upsell email to engaged subscribers: Publishers can edit the message and add or remove their own offers. Review the subject and body copy, the paid benefits being promised, the destination and the displayed terms. If the default incentive is removed or replaced, check that no obsolete discount language remains.
• Multiple-subscription discount: Participation allows a publication to appear in discounted recommendations after readers pay for another Boost-enabled publication. Other publications may likewise be recommended to your new paid subscribers. The documentation identifies an individual participation control but does not describe publisher editing of the upsell copy or percentage, so the email’s customization rights should not be assumed here.
• Pre-cancel offer: This intervenes during cancellation for eligible paid subscribers. The documented incentive is presented as a defined Boost offer rather than a publisher-configured duration or editable message. Review whether the concession fits the publication’s retention policy and any separate cancellation incentives.
• Master control: Disable the publication-wide setting if no Boost-selected promotional moment should reach readers. Turning off one mechanism suppresses that mechanism; it is not the same as opting out of the complete system.

The central distinction is between participation control and content control. The engaged-subscriber email is explicitly customizable, while the documented network and cancellation mechanisms provide narrower controls.

Boost is not the whole promotion system

Disabling Boost does not necessarily remove every promotion configured for a publication. Substack’s monetization feature inventory separately lists plan-level free trials, coupons and discounts, gift subscriptions and cancellation offers. Those tools need their own audit outside the Growth area.

A paywall trial is one concrete example. The paywall-trial instructions document a separate seven-day trial controlled under Payments: readers select a subscription plan and enter card details, and the paywall message cannot be customized.

This separation matters when a publisher intends to end all discounting rather than only Boost automation. A disabled Boost toggle does not, by itself, establish that trials, coupons, gifts or independently configured cancellation offers are inactive.

Audit every offer before enabling it

1. Record the master state. Open the publication’s Growth settings and note whether the publication-wide Boost control is enabled before inspecting individual mechanisms.
2. Inventory each mechanism. Record the state of the engaged-subscriber email, multiple-subscription discount and pre-cancel offer. Do not infer one setting from another.
3. Review editable copy. Inspect the engaged-subscriber email’s message, promised benefits, destination and offer terms. Make sure the wording still matches any incentive that has been added, changed or removed.
4. Approve the economics separately. Decide whether the conversion-email discount fits acquisition policy, whether the network discount is acceptable and whether the cancellation concession suits the value and cadence of the paid publication.
5. Match mechanism to audience. Separate selected free subscribers, readers completing payment elsewhere in the network and existing paid subscribers attempting to cancel. An offer appropriate for one group may be unsuitable for another.
6. Inspect settings outside Growth. Check Payments and any active trials, coupons, special offers, gifts or cancellation incentives. This prevents a Boost opt-out from being mistaken for a publication-wide end to promotions.
7. Save and verify the opt-out state. Leave unsuitable mechanisms unselected. If no Boost-generated offer should run, disable the master control and confirm that the setting remains off after saving.

Choose an approval threshold for each mechanism

Approve the engaged-subscriber email only when its editable copy and incentive are acceptable. Approve the multiple-subscription discount only when participation in the network upsell fits the publication’s acquisition policy, and approve the pre-cancel mechanism only when its retention concession is consistent with existing subscriber terms.

If the documented controls are too limited for a particular offer, leaving that mechanism disabled preserves the clearer boundary. If the publication does not want Substack choosing promotional moments in the background, the master opt-out is the relevant control.