Allocating Inventory Across 4 Channels

You have 800 units of a hero SKU coming off the water. TikTok Shop wants velocity for the algorithm. Amazon needs a 60-day FBA buffer. Etsy is a long-tail trickle. Shopify is your highest-margin channel but has the lowest unbranded discovery. How do you split the inventory? The answer is a framework, not a feeling.

Why allocation matters more than most sellers recognise

Inventory allocation is a capital allocation decision. When you put 400 units at Amazon FBA, you are committing that capital — and that physical product — to a specific channel's economics for the duration of the sell cycle. You cannot easily reallocate once inventory is received at FBA. Making that decision based on gut feeling rather than channel-level net profit per unit is equivalent to allocating your investment portfolio without knowing which assets you own.

The compounding effect of good allocation is substantial. Over a year, consistently allocating 10% more inventory to your highest-net-profit channel and 10% less to your lowest adds up to meaningful P&L improvement without any change in COGS, pricing, or marketing spend. Allocation is one of the few levers in e-commerce that costs nothing to pull and improves almost immediately.

The allocation framework

Allocate by net profit per unit, weighted by sell-through velocity, capped by channel-specific operational requirements. The formula: channel allocation = minimum of (channel operational cap, total units × (channel net per unit × channel weekly velocity) / sum of all weighted channel scores). This formula ensures your highest-net, highest-velocity channels get disproportionate inventory while respecting the minimum buffer requirements that each channel needs to function.

Channel operational caps are real constraints: Amazon FBA requires enough inventory to maintain in-stock status without triggering long-term storage fees; TikTok Shop live-commerce requires burst capacity for sale events; Shopify requires a safety stock buffer if you are running paid advertising (stockouts mid-campaign are expensive); Etsy can run on very thin inventory for limited-edition positioning.

The 800-unit example worked through

Using illustrative numbers: Shopify nets $12/unit at 80 units/week (score: 960), Amazon nets $8/unit at 200/week (score: 1,600), TikTok nets $7/unit at 120/week (score: 840), Etsy nets $9/unit at 25/week (score: 225). Total weighted score: 3,625. Pure formula allocation: Amazon gets 353 units, Shopify 212, TikTok 185, Etsy 50.

Apply operational minimums: Amazon FBA needs at least 240 units for a 6-week buffer at 40 units/week average (velocity can spike). TikTok needs at least 150 for the algorithm to stay engaged and handle a live event spike. Shopify needs at least 100 for ad campaign coverage. Etsy can run with 20–30. After minimums are covered: Amazon 280, Shopify 170, TikTok 150 + reserve, Etsy 30, buffer/unallocated 50 for reorder flexibility.

Allocate to the math, override for the calendar.

Safety stock and lead time

Safety stock is the inventory you hold above your expected demand to protect against demand spikes and supply disruptions. The standard safety stock formula is: Z × standard deviation of daily demand × square root of lead time in days, where Z is your service level factor (1.65 for 95% in-stock rate, 2.05 for 98%). For a product selling 40 units/day with 5-day demand standard deviation and a 60-day lead time, a 95% service level requires roughly 65 units of safety stock.

Most small sellers do not need the full statistical model but should operate with a mental model of: order when remaining inventory hits lead time demand plus a buffer of 20–30%. For a product with a 60-day replenishment lead time selling 10 units/day, the reorder point is (60 × 10) + 200 = 800 units remaining. Waiting until 500 units to reorder a 60-day lead time product is how stockouts happen.

The calendar override layer

The mathematical allocation framework is the default. Override it deliberately and temporarily for specific calendar reasons: Amazon's Prime Day and Black Friday/Cyber Monday require inventory pre-positioning 6–8 weeks in advance; a TikTok creator collaboration or live event requires burst capacity on short notice; Shopify campaigns tied to holidays need inventory protection; Etsy's gifting seasons (Valentine's Day, Mother's Day, Christmas) drive disproportionate trickle-channel volume.

Document your overrides and their rationale. After each event, compare the actual channel performance against the formula-based baseline. Over time, this comparison tells you whether your calendar overrides are generating better returns than the formula would have, which is the only way to know whether your qualitative judgement is adding value above the quantitative framework.