Profit Hawk
Free tool · For Amazon FBA sellers

Inventory Days of Supply Calculator
for Amazon FBA sellers.

See how many days of cover your Amazon inventory provides — sellable FBA only, plus inbound, plus AWD/3PL — at your real daily sales pace.

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What question does this answer
“How many days of inventory cover do I have before this Amazon SKU runs out?”

Calculate your days of supply

Enter your current inventory and recent daily sales. We'll show three levels of cover — sellable only, with inbound, and including AWD/3PL.

units
units
units
units
Strip stockout days from your sales window

If your last 30 days included any days where the SKU was out of stock, your average will be depressed and the days of supply will look bigger than it really is. Use a 30–60 day window with stockout days removed, or the longest fully-in-stock stretch you have.

Total days of supply
90days
Healthy cover
Total units across all locations
1,800units
Healthy band
30–90days

What this meansPlain English

At 20 units/day, total cover (FBA + inbound + AWD/3PL) is 90 days. Comfortable cover — monitor your reorder point and you'll stay ahead of the next PO cycle.

Days of supply kit

Turn your 90-day cover into a replenishment plan

Get a practical kit for ranking SKU coverage, spotting overstock and stockout risk, and turning days of supply into reorder decisions.

  • PDF of this calc — 90 days cover · 600 units · 20/dayInstant
  • Multi-SKU template — for ranking inventory cover by productSheet
  • Extended calculator — rolling demand windows + multi-warehouse cover scenariosTool
  • 5-day FBA playbook — inventory coverage cleanup, one short email a dayCourse
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How it works

The formula, in plain English.

Days of supply is the simplest inventory metric there is — but the question is which inventory to count. We compute three views: FBA-only, with inbound, and including external stock.

Days of Supply =Units ÷Avg daily sales
FBA
FBA sellable only. Units in Amazon FCs that can ship today. The tightest view — and the one Amazon's own dashboards usually show.
+ inbound
With inbound / on-order. Add units already in transit, at the freight forwarder, or at Amazon receiving. The fairest view for reorder timing.
+ AWD/3PL
Total available cover. Add AWD or 3PL stock that can be shipped to FBA. The full picture for sellers running multi-warehouse.
d̄
Average daily sales. The denominator. Pull 30–60 days of unit sales from a fully-in-stock window — stockout days depress the baseline.

Worked example

A mid-velocity hero SKU with a PO in transit and AWD backup.

FBA sellable600 units
Inbound / on-order900 units
AWD / 3PL300 units
Average daily sales20 units
DOS — FBA only30 days
DOS — with inbound75 days
Total days of supply
90 days
Watch out for

Common days-of-supply mistakes.

The math is elementary; the inputs are where sellers go wrong. Here are the assumptions that quietly distort the number.

01

Only counting FBA sellable

Ignoring inbound, AWD, and 3PL stock means your reorder triggers fire too late and you over-order on SKUs that already have plenty incoming.

Fix: Always compute three views — FBA only, FBA + inbound, and FBA + inbound + external.
02

Pulling sales from a stockout window

If your 30-day average includes any zero days, your run-rate is depressed and the DOS number is artificially flattering.

Fix: Use a fully-in-stock window of 30–60 days, or strip stockout days from numerator and denominator.
03

Treating all SKUs with one healthy band

A high-velocity hero SKU and a long-tail variation need very different cover. Blanket targets either over-stock the tail or under-stock the head.

Fix: Tier the catalog and apply different DOS targets per tier and per season.
04

Ignoring seasonality

60 days of cover on July 1 might be 'overstocked' for a winter SKU, or 'urgent' for a back-to-school item. Static thresholds don't fit seasonal products.

Fix: Layer in expected seasonal velocity before judging if DOS is healthy.
05

Forgetting Amazon receive time

Inbound units don't help if they sit at Amazon receiving for two weeks before going sellable. Treating all inbound as immediate cover misleads the trigger.

Fix: Discount inbound by realistic Amazon receive lag — usually 1–3 weeks depending on FC.
06

Letting overstock go unmanaged

Above 90 days of cover, Amazon long-term storage fees and aged-inventory risk are quietly piling up while you watch the urgent SKUs.

Fix: Flag overstocked SKUs the same way you flag urgent ones — promote, mark down, or remove.
When this calculator isn't enough

Great for one SKU.
Painful for a real catalog.

This tool is perfect for sanity-checking one SKU. But across a real Amazon catalog, days of supply is moving every day — and manual math doesn't scale.

  • Seasonality & promo spikesRun rate during Prime Day or Q4 isn't your baseline — DOS calculated off peak velocity will spook you into overstocking.
  • Receive lag and FC dwell timeInbound that's stuck at receiving doesn't actually buy you days of cover until it goes sellable.
  • Multi-marketplace catalogsUS, CA, UK, and EU each have their own velocity and warehouse mix. One blended DOS hides where the real risk is.
  • FBA + AWD + 3PL togetherA complete picture means combining warehouses and inbound — manually keeping that in sync gets unreliable fast.
  • Long-tail SKU countHundreds of SKUs means hundreds of DOS calculations. The math is simple; the operational discipline isn't.
  • Cash impact of overstockDOS shows the symptom. Connecting it to cash tied up and excess units takes a different calculation.
▲ Profit Hawk

Track days of cover across every SKU, continuously.

Profit Hawk pulls FBA, AWD, 3PL, and inbound inventory from Seller Central and recalculates days of supply for every SKU — flagging urgent and overstocked items before they cost you money.

  • Per-SKU DOS across FBA + AWD + 3PL + inbound
  • Urgent / healthy / overstocked sorting at catalog scale
  • Seasonality & promo-aware demand
  • Replenishment alerts tied to reorder points
Start free trialSee Profit Hawk →
FAQ

Days of supply, answered.

The questions Amazon sellers actually ask about days of supply — what to count, how to handle messy data, and what a healthy number really looks like.

Should I count inbound and AWD/3PL stock or just FBA on-hand?
Count everything that can realistically be sellable on Amazon before the next PO arrives — FBA sellable, FBA inbound, AWD, and 3PL. If you only look at FBA on-hand you'll constantly under-buffer and reorder too late. The tool gives you all three views so you can see where each cushion sits.
What counts as a 'healthy' days-of-supply range?
For most FBA sellers, 30–90 days of total cover is the practical band. Below 30 days you're inside most suppliers' lead time and one delay means a stockout. Above 90 days you're risking Amazon long-term storage fees and tying up cash that could be deployed elsewhere. Hero SKUs sometimes sit higher; long-tail seasonal items often sit lower.
How is days of supply different from days of cover?
They're used interchangeably. Both mean: current inventory ÷ average daily sales = the number of days you can sell before you run out. Some software splits them (DOS for sellable only, DOC for total including inbound), but in practice most sellers and operators treat them as the same metric.
Should I include reserved or unfulfillable units?
No — only count units that are sellable today. Reserved (in carts or transfers), unfulfillable, and researching units don't generate revenue. If your Inventory Ledger shows a big reserved bucket, dig into why — it's often a transfer that's about to clear.
What if my average daily sales include a stockout?
Your DOS will look bigger than it really is. Pull a window with no stockout days — usually the longest fully-in-stock stretch in the last 60–90 days. If you can't get a clean window, manually subtract the stockout days from both the unit total and the day count before dividing.
How often should I recalculate days of supply?
At least weekly for hero SKUs and at every PO decision for the rest. Days of supply moves with both your sales velocity and your incoming POs — a number that was healthy on Monday can be urgent by Friday after a sales spike. Inside Profit Hawk we recalc continuously.
Why is overstock as much of a problem as understock?
Long-term storage fees on Amazon escalate at 271+ days, and aged inventory often ends up sold at a steep discount or destroyed. Cash sitting in 120+ days of inventory could be funding a faster-moving SKU or a new launch. Days of supply gives you the early signal.
Should I use the same target days of supply for every SKU?
No. Hero SKUs and seasonal items have very different right answers — a Mother's Day SKU at 90 days in March is healthy; at 90 days in June it's a write-down. Tier your catalog and set target ranges per tier and per season.
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▲ Profit Hawk

Want days of cover tracked across every Amazon SKU?

Profit Hawk recalculates days of supply continuously using your real Amazon sales, FBA + AWD + 3PL inventory, and inbound shipments — and flags urgent and overstocked SKUs before they cost you money.

Start free trialSee Profit Hawk