The short version: a replenishment flow reminds the customer to reorder before the bottle runs out, timed off their actual consumption cycle rather than a marketing calendar. The engagement data makes it the strongest lifecycle email in ecommerce: Ometria's data puts replenishment emails at 50 to 60% open rates, 40 to 50% click-through, and 10 to 15% conversion, and Listrak measured the highest click-to-open rate of any email marketing type at 53.6%. For a consumable category like supplements, a missing replenishment flow is a real fraction of email revenue left on the table, and most brands are missing it.
Why this flow is unreasonably effective for supplements
Every supplement product has a built-in clock: a 60-capsule bottle at two a day is a 30-day cycle, no modeling required. The customer will need more on a knowable date, and the only questions are whether they reorder from you or drift to Amazon, and whether they reorder at all instead of quietly lapsing. A replenishment email arriving a few days before empty answers both: it is genuinely useful (the customer experiences it as service, not marketing, which is why the engagement numbers look nothing like promotional email) and it captures the reorder at the exact moment of highest intent.
It is also the adherence lever wearing a revenue costume. The customer who runs out and goes a week without is the customer who never feels the results and never comes back. Keeping the streak unbroken is retention strategy disguised as a shipping reminder.
The timing math
Three inputs: purchase date, consumption rate, and a lead-time buffer.
- Days of supply per product: units in the package divided by the label's daily serving. A 60-capsule, two-a-day bottle is 30 days. Store this as a per-product property or in the flow's conditional splits.
- The trigger point: roughly 70 to 80% of the cycle. Klaviyo's guidance for a 30-day supply product is a 20-to-25-day delay: the reminder lands while supply remains, leaving time to ship before empty. We build at day 24 on a 30-day cycle. A reminder after empty is a winback problem you created yourself.
- Refine with observed behavior. Once a customer has two or more orders of the same product, their actual median reorder gap beats the label math: the two-a-day label customer who reorders every 45 days is telling you their real consumption. Trigger from purchase-level data where you have it, category math where you do not.
- Quantity-aware entry: a three-bottle order is a 90-day clock, not 30. Multiply days of supply by quantity at entry, the most common bug in replenishment builds.
The build: three emails, then stop
Email 1: day 20 to 24 of a 30-day cycle. The useful reminder
By our math you are running low. One product image, remaining-days framing, one-click reorder that lands in a prefilled cart. No discount: the customer needs the product, and this send converts on usefulness. Include the subscription option beside the one-time reorder in every send of this flow: someone actively reordering is the perfect subscription prospect, and never running out again is the honest pitch.
Email 2: at or just before empty. The streak email
Frame the cost of the gap, compliantly: consistency is how this category works, a two-week gap resets progress. Reorder now and it arrives before you run out (or barely after). Still no discount.
Email 3: 7 to 10 days past empty. The recovery nudge
Now they have lapsed, and the calculus changes: a small incentive here is defensible because the alternative is the winback flow's steeper discounts later. Free shipping or loyalty points before a percentage. After this send, exit: the profile belongs to the behavioral flows and eventually winback. A fourth or fifth replenishment nag teaches people to ignore the useful emails too.
Suppression and routing, where these builds live or die
- Active subscribers never enter. Their replenishment is the subscription itself; a reorder reminder to a subscriber reads as your systems not talking to each other. Suppress on active-subscription status per product, not just brand-wide.
- A new purchase of the same product resets the clock: flow filter checks for a more recent order at every send.
- Subscription start exits the flow immediately, the best possible outcome. Track it as a flow conversion alongside reorders.
- Multi-product buyers get per-product clocks, but cap sends so a five-product customer is not getting five overlapping reminder tracks: consolidate into a single running-low digest where cycles land within a week of each other.
The subscription bridge
The replenishment flow is quietly your best subscription acquisition channel. The customer opening a running-low email has demonstrated exactly the problem subscribe-and-save solves, so every email in the flow carries the subscription option, and the flow's real success metric is not reorder rate alone but the share of entrants who convert to subscription and exit the reminder treadmill permanently. Price the comparison honestly and show the skip and cancel controls: the welcome flow made this case on trust grounds, and the replenishment flow makes it on convenience grounds at the moment of need.
What to measure
- Open and click rates against the lifecycle benchmarks (50 to 60% opens, 40 to 50% clicks): materially below means the timing math is wrong for your products, usually quantity-blind entry
- Conversion against the 10 to 15% band, on orders
- Subscription conversions from the flow, counted as wins equal to reorders
- Lapse rate at cycle-plus-14-days for flow entrants versus pre-flow baseline: the retention number the flow exists to move
Frequently asked questions
When should a replenishment email send?
At roughly 70 to 80% of the product's consumption cycle: Klaviyo's guidance is a 20-to-25-day delay for a 30-day product, adjusted by order quantity and, once available, the customer's own observed reorder gap.
Should replenishment emails include a discount?
Not the first two: they convert on usefulness at full margin. A small value-add incentive is defensible only in the final send to already-lapsed customers, as the cheaper alternative to winback discounts later.
How is replenishment different from winback?
Replenishment is proactive, timed to predicted run-out, and feels like service. Winback is reactive, triggered by absence, and costs more per recovered customer. A working replenishment flow shrinks the winback pool.
Do subscribers get replenishment emails?
No. Suppress on active-subscription status per product. The flow's job for non-subscribers is the reorder and, ideally, the subscription conversion that removes them from the flow forever.
What does a replenishment flow convert at?
Ometria's published data puts replenishment emails at 10 to 15% conversion, with Listrak measuring the highest click-to-open rate of any email type at 53.6%, driven by timing usefulness rather than persuasion.