What happens to your Shopify Black Friday sale when its units already sit in FBA? Learning how to split FBA and Shopify inventory for BFCM settles that before your product page shows sold out.
Most brands choose a round split like 70/30 in November. By then, Amazon’s October arrival dates have already capped each channel.
We manage over $1.2B in ecommerce revenue across 400+ brands, often running Shopify and Amazon inventory solutions for the same company. That view turns the split into two floors.
Our agency talks about those floors and the dates that lock them in this marketplace guide. We also discuss MCF costs, bulky SKUs, a worksheet, and KPIs.
Send your stock by SKU, and we'll map each floor for free.
Part One. Why One FBA Pool Breaks at Peak
Many Amazon-native brands run two channels from one pool. It holds in July and breaks in November.
What happens when Amazon and Shopify draw from the same FBA inventory?
Every Shopify order sent through Multi-Channel Fulfillment uses FBA units Amazon needs. The Amazon MCF app for Shopify hands your store orders to Amazon to ship, so a busy Shopify weekend drains Amazon stock.
Amazon keeps pulling Shopify buyers into that pool. At 0:22, this video explains an MCF beta offering Prime-style shipping to non-Prime DTC shoppers.
Why can’t I just send more stock to FBA in November?
Amazon won’t guarantee processing for late units. Its centers also prioritize holiday receiving in September and October, so lock the split early.
Can I still use AWD as my BFCM buffer?
AWD no longer accepts oversized items, because it stopped taking new sellable units at or above 18 x 14 x 8 inches or 20 pounds on July 31, 2026. Those AWD size limits leave bulky inventory with three lanes.
- Direct FBA
- A third-party logistics fallback
- FBM
AWD can’t ship Shopify parcels either. MCF draws from FBA inventory, not AWD.
Misconceptions to clear first
- A split is a fixed percentage
- Sync software sets the split
- FBA serves Shopify at no cost
- More FBA units means safety
Sync tools block double sales but never size channels. Extra FBA units feel safe until Q4 storage bills land.
Part Two. The Two-Floor Math That Sets Your Split
Learning how to split FBA and Shopify inventory for BFCM starts with two floors. Set Amazon’s floor first, since it carries the tighter deadline and the steeper penalty.
The two floors, compared
| Floor | What sets it | What breaks below it |
|---|---|---|
|
Amazon floor |
35 days of supply per FNSKU, above the 28-day fee line |
Low-inventory fees, lost sales, slipping rank |
|
Shopify floor |
Cyber Week Shopify forecast plus a sync buffer |
Oversells and sold-out pages still receiving paid traffic |
Your FBA shipments and MCF volume set the Amazon floor’s stock levels. Your warehouse or 3PL controls the Shopify floor.
What does it cost to land on the wrong side of each floor?
Many sellers cite an Amazon low inventory level fee 35 days threshold, but the real line sits lower. The fee starts when days of supply drops under 28 on both the 30-day and 90-day windows, costing $0.32 to $1.11 per standard unit and about $2.09 per bulky unit.
Keep 35 days of cover since Black Friday can drain inventory quickly.A stockout also hurts rank, and recovery can take weeks.
Below the Shopify floor, your ads steer shoppers to a sold-out page. Adobe data cited by Shopify shows Black Friday online sales grew 9.1% in 2025.
One low-stock warning ends differently on each channel. A sold-out Shopify page loses the sale, while a stocked Amazon listing still converts.
Over-shipping FBA costs money too. Standard storage climbs from $0.78 to $2.40 per cubic foot in October, and minimal splits add inbound placement fees.
So does covering Shopify through MCF. MCF peak fulfillment fees 2026 run October 15 to January 14, 2027, plus a 3.5% multi-channel fulfillment surcharge, and peak adds run $0.35 to $1.00 per unit.
That squeezes a thin FBA vs Shopify margin per unit gap. We modeled $9.80 on a $100 order, and peak MCF shrinks it.
Split targets by revenue stage
These are the planning standards our team uses on managed accounts. Grade your process against them.
- Average $1M to $5M brands set one split in November
- Good $1M to $5M brands write SKU floors by October 14
- Average $5M to $20M brands check stock weekly
- Good $5M to $20M brands name an owner and read cover daily
Brands miss those targets for five common reasons. Each one makes both floors hard to set.
Part Three. How to Split FBA and Shopify Inventory for BFCM, Step by Step
One planning session covers all six steps. Work them in order.
Step 1. Count sellable units against the arrival dates
Count only sellable units, skipping stock stuck in FC transfer or receiving. Your FBA inbound deadline Black Friday 2026 plan then runs on three arrival dates.
- AWD stock lands by October 14
- Minimal-split FBA shipments land by October 21
- Amazon-optimized splits land by October 28
Step 2. Set the Amazon floor for each SKU
Multiply each SKU’s Cyber Week daily velocity by 35. Q4 demand can run 20% to 40% above average weekly sales, so inventory management strategies should ignore September’s run rate.
A SKU selling 40 units a day needs 1,400 units in FBA. With 2,000 sellable units, Shopify starts with 600 before you test its floor.
Start with top sellers, since 10% to 20% of SKUs often drive 70% to 80% of BFCM revenue. Brands seeking an Amazon agency for inventory planning can hand this to our Amazon marketplace services team, which runs Shopify and Amazon inventory management for the same brands.
Step 3. Give Shopify what remains, then test its floor
Subtract the Amazon floor from sellable units and compare the rest with your Shopify forecast. A shortfall forces one channel to run lean.
Full-funnel growth marketing settles that by giving each channel a job. Our Amazon vs Shopify breakdown assigns Amazon volume and Shopify margin.
Buy with Prime sits where those jobs overlap. It fills Shopify orders from FBA stock, so count those units against Amazon’s floor.
Step 4. Set the reserve on the lane you control
Shopify’s Marketplace Connect quantity rule sets a fixed value, buffer, or maximum for store stock shown on Amazon, keeping it synced with your Shopify inventory management system. That Marketplace Connect inventory buffer covers merchant-fulfilled offers only and skips existing listings, so edit those during Marketplace Connect setup for Amazon.
Hold back a few Shopify units, as Katana shows 45 of 50, to protect your seller health score. On Marketplace Connect vs third-party inventory sync, keep your current tool.
Our ecommerce builds team sets up Shopify locations that separate FBA and 3PL stock. Clean setup beats chasing the best inventory sync app for Amazon and Shopify.
Step 5. Route bulky SKUs and open a fallback lane
Price each bulky SKU across direct FBA, a 3PL, and FBM. MCF cuts per-unit fees up to 50% on multi-unit orders, so single units absorb the worst of MCF peak fulfillment fees 2026.
Then pick a Shopify fallback lane to prevent oversell during high demand. The MCF vs 3PL and FBM vs MCF calls usually break this way.
- MCF fits multi-unit Shopify orders
- A 3PL fits single-unit and bulky orders
- FBM keeps Amazon live after FBA sells out
Our logistics management team builds third-party logistics fallback lanes around accurate inventory forecasts. Secure your 3PL early since most stop taking stock 7–10 days before Black Friday.
An FBM backup when FBA runs out keeps you selling, since FBM beats an out-of-stock page. Our Dual-Front System guide shows how to run FBA and FBM together and manage stock levels across both.
Step 6. Set a freeze date and rebalance triggers
Freeze the split once your last FBA shipment leaves. After that, only written triggers move units.
- Amazon cover under 35 days shifts 3PL stock to FBM
- Shopify cover under five days pauses that SKU’s ads
Triggers work best as yes-or-no paths like this one. Send email traffic to Amazon only while FBA stays above 35 days.
An Amazon-only price hike can cost the Featured Offer, so follow our pricing rules. For leftovers, owned email has turned DTC demand into Amazon revenue and cleared expiring inventory.
The BFCM split worksheet
| Column | What to enter | Source |
|---|---|---|
|
SKU |
One row per FNSKU |
Seller Central |
|
Sellable units |
Stock that beats the cutoff |
Seller Central, 3PL |
|
Amazon daily velocity |
Cyber Week units per day |
Business Reports |
|
Amazon floor units |
Velocity times 35 |
This sheet |
|
Shopify forecast |
Cyber Week Shopify units |
Shopify reports |
|
Shopify floor units |
Forecast plus sync buffer |
This sheet |
|
Surplus or shortfall |
Sellable units minus both floors |
This sheet |
|
Fulfillment lane |
FBA, MCF, 3PL, or FBM |
Step 5 |
|
Ship-by date |
Pickup that meets the cutoff |
Step 1 |
Use it as your BFCM inventory planning template. Shortfall rows become this week’s calls.
Common execution mistakes
- Counting units still in transfer
- Using one split for every SKU
- Buffering the wrong channel
- Assuming AWD takes bulky units
- Skipping an agreed freeze date
- Raising only the Amazon price
What We've Seen Across Managed Accounts
When demand moved off Amazon
Our fishing kayak brand client sells bulky, seasonal goods AWD excludes. By early 2026, its Amazon category had dropped about 50% while tariffs added cost pressure.
We built Google Ads on Performance Max and Search and launched Merchant Center for the brand’s store. That full-funnel growth marketing shifted where buyers checked out.
- 98% more website revenue in 8 months
- Paid search clicks up from 11k to 39k
- 59% more website orders
- Click-through rate up from 0.84% to 1.22%
The study tracked revenue, not stock. That growth lifts the Shopify floor, so how you split FBA and Shopify inventory for BFCM must follow demand.
Warning signs from three other accounts
These records show no final outcomes. Treat them as warnings.
A packaged-goods brand ran short on FBA stock while units sat in transfer. The team raised the Amazon price about 10% to slow sales.
A home-textile maker sold stranded FBA units on Shopify and Etsy via manual MCF orders. The team flagged about 36 units, and 33 remained later.
A tracking-equipment seller found bulky size tiers in its MCF report. Those fees prompted a multi-unit pricing review.
Book a BFCM inventory planning call before October 21.
Measuring Your BFCM Inventory Split
The true test of how you split FBA and Shopify inventory for BFCM arrives after peak. Track both channels on one sheet until then.
KPIs to track by channel
- Days of cover per channel
- Low-inventory fees by FNSKU
- MCF share of FBA units
- Sellout days on Shopify
- Stranded units in Seller Central
- Contribution margin per channel
Cover and fees grade the Amazon floor. Sellout days and MCF share show if Shopify borrowed too much.
Reporting cadence and tools
Pull Seller Central restock reports, Shopify inventory reports, and real-time inventory forecasting data. Review them on this rhythm.
- Weekly through October
- Daily through Cyber Week
- A full reconciliation in January
Our 12 Seller Central reports for Shopify strategy list the files to pull. Full-funnel growth marketing reads both channels as one P&L, so judge the split on combined margin.
Advanced Tactics Once the Split Holds
Once your floors survive a peak, widen the buffer. These moves suit brands with a steady 3PL.
How do I build an outside buffer for bulky SKUs?
Park bulky stock at a 3PL and send FBA smaller, frequent shipments. For small units, Amazon says Q4 2025 AWD users shipped over 13% more units with over 30% fewer out-of-stock days.
Should overflow stock go to Walmart or another marketplace?
Our Walmart marketplace services team places surplus in front of Walmart holiday shoppers. Our other marketplaces team lists the rest on channels like TikTok Shop, compared in our TikTok Shop vs Amazon guide.
More Resources on Peak Inventory and Multichannel Selling
FAQs on How to Split FBA and Shopify Inventory for BFCM
How much inventory should I send to FBA for Black Friday if I also sell on Shopify?
Send 35 days of peak supply per SKU and give Shopify the rest, keeping stock levels above both floors. The fee line sits at 28 days, so 35 adds room.
Can I use FBA inventory to fulfill Shopify orders during BFCM?
Yes, MCF allows it, but each order drains Amazon stock. Cap MCF volume in your worksheet.
Does Multi-Channel Fulfillment cost more during peak season?
Yes, especially on single units. Peak fees cover MCF through January 14, 2027.
What happens when FBA inventory drops below the low-inventory threshold?
Amazon charges a fee on each unit sold until cover recovers. It now applies per FNSKU, bulky included.
What’s the last day to send inventory to Amazon for BFCM 2026?
Optimized splits arrive by October 28 and minimal splits by October 21. AWD stock lands by October 14.
Can I still send bulky products to AWD before Q4?
AWD rejects new units at or above 18 x 14 x 8 inches or 20 pounds. Route them to FBA, a 3PL, or FBM.
Does Marketplace Connect reserve my FBA inventory?
No, it only caps store inventory shown on Amazon. Use it for merchant-fulfilled offers.
Is it normal to sell out on Shopify before Amazon?
Yes, when most stock sits in FBA. Early December is a common stockout window, so keep checking.
Should I raise my Amazon price to avoid a stockout?
Only after off-Amazon prices move, or you risk the Featured Offer. An FBM backup when FBA runs out works better.
Your Split Is a Floor, Not a Guess
October decides your BFCM split. Brands that stay in stock on both channels write their floors first.
- Set Amazon’s floor first
- Shopify gets what remains
- October dates lock everything
- Reserve on the lane you control
- Judge the split in January
Amazon-native owners should run Steps 1 and 2 this week. Knowing how to split FBA and Shopify inventory for BFCM by October 14 leaves time to ship.
Ecommerce directors should hand the worksheet to whoever owns purchase orders, so every PO matches both floors. Full-funnel growth marketing only works when inventory, ads, and email follow one split.
Our logistics team builds your floors, fallback lanes, and ship-by dates before October closes.