After Prime Day: Replenishment Planning for Q3 (2026)

Seasonal playbook · 2026

Quick answer: The SKUs that won Prime Day are the ones most likely to stock out in Q3 — the event drained the exact inventory your best products needed for the rest of the summer. The replenishment plan: recompute every winner’s days of supply using its normal (spike-excluded) velocity, compare that number to your real lead time, and reorder anything where coverage is inside the lead-time window — this week, not at month-end. Sellers who wait for the monthly reorder cycle discover the gap in August, which is exactly when the purchase order can no longer arrive in time.

Last week we covered the leftovers — the SKUs Prime Day didn’t move. This is the other half, and it’s the half that actually costs you rank: the winners.

A SKU that did four times its normal volume over the event didn’t just have a good week. It quietly spent the stock that was supposed to cover July and August. And because the sales graph looks fantastic, nobody treats it as an emergency — until the days-of-supply number catches up with reality a few weeks later.

Why post–Prime Day stockouts happen in August, not July

The mechanics are boringly predictable. Say a winner sells 15 units a day normally, and the event days ran hot. After Prime Day you’re holding 900 units. Feels like plenty — two months of cover, right?

900 units ÷ 15/day = 60 days of supply
With a 75-day lead time, a PO placed today is already 15 days late

Sixty days of supply sounds healthy. Against a 75-day lead time, it’s a scheduled stockout in mid-September — and every day you wait to place the order moves that date closer while doing nothing to the delivery date. The reorder point already passed; the dashboard just didn’t say so.

A stockout in September is almost never a September mistake. It’s a July decision that didn’t get made.

The five-step replenishment pass (do it this week)

1. Correct the velocity first

Exclude (or cap) the event days when you compute average daily sales, or every number downstream is inflated. But check the post-event run rate too — some winners settle at a permanently higher baseline because Prime Day brought new customers and review velocity. Use the settled rate, not the spike and not last quarter’s nostalgia.

2. Recompute days of supply on every winner

Units on hand (including anything already inbound) divided by the corrected daily rate. Do this per SKU and per channel — a healthy total can hide an empty FBA position if most of your stock is sitting at a 3PL.

3. Compare coverage to lead time, not to a round number

The only threshold that matters is your real, end-to-end lead time — PO placed to unit sellable — plus safety stock. If days of supply is inside that window, the SKU is already late. If your lead time is a guess, fix that first; it’s the input that decides whether this whole exercise tells the truth.

4. Size the PO for Q4, not just for the gap

With 60–90 day lead times, the order that patches your August hole is the same order that positions you for October. Sizing it only to refill the summer gap means placing another PO four weeks later — and paying rush freight on the second one. Look at the whole horizon through Black Friday before you set the quantity.

5. Stage the inbound sensibly

Replenishing FBA doesn’t have to mean sending the whole order to Amazon at once. Splitting the buy between FBA and upstream storage (AWD, a 3PL, your own warehouse) keeps peak-season storage costs down while protecting availability — drip stock in as it sells.

The honest caveat: not every Prime Day winner deserves a big reorder. Some spikes are pure discount response — the demand evaporates with the coupon. Before you place a large PO, ask whether the post-event run rate confirms real lift. And remember the opposite failure exists too: running winners too lean invites Amazon’s low-inventory-level fee and hands your rank to whoever stayed in stock. Both directions cost money; the corrected velocity number is what keeps you between them.

The part nobody automates: making it a ritual

None of the math above is hard. What fails is the cadence — velocity gets recomputed “when someone has time,” which after a big event is exactly when nobody has time. The sellers who avoid Q3 stockouts are the ones for whom per-SKU days of supply is a number they see weekly, not a spreadsheet they rebuild quarterly. Whether that’s a tool or a standing Monday meeting matters less than that it happens on a schedule.

Know which winners are quietly running out

Connect your Amazon and Shopify data and SKU Compass shows per-SKU, per-channel velocity, days of supply, and reorder points built from your own lead times — so the August stockout shows up in July, while you can still do something about it. Free for 30 days, no credit card.

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Frequently asked questions

How soon after Prime Day should I reorder?

Within the first two weeks. With typical 60–90 day lead times, a winner that came out of the event with under ~75 days of supply is already at or past its reorder point. Waiting for a monthly reorder cycle is how July gaps become September stockouts.

How do I know if a Prime Day spike is real demand?

Watch the post-event run rate for two to three weeks. If daily sales settle back to the old baseline, the spike was discount-driven — replenish to the old velocity. If they settle higher, the event bought you new customers and reviews; replenish to the new baseline instead.

What is the formula for a reorder point?

Reorder point = (average daily sales × lead time in days) + safety stock. After a promo event, the critical discipline is using spike-corrected average daily sales and a real end-to-end lead time — PO placed to unit sellable, not just factory time.

Should I send my whole replenishment order to FBA?

Usually not during peak-fee season. Many sellers split the order between FBA and upstream storage (AWD, a 3PL, or their own warehouse) and drip stock into FBA as it sells — protecting availability while limiting exposure to October–December storage rates.

What happens if I let a bestseller stock out on Amazon?

You lose more than the missed sales — the listing loses sales rank and momentum, ads lose efficiency, and recovering position after restocking takes time. That compounding cost is why replenishing winners beats almost any other inventory task on ROI.

How is this different from clearing Prime Day leftovers?

They’re the two halves of the same post-event pass: leftovers are SKUs the event left overweight (a fee problem), winners are SKUs it left underweight (a stockout problem). Same corrected-velocity math, opposite actions. Run both in the same week.