Inventory Aging Analysis: A Practical Guide

Inventory aging measures how long stock has sat since it arrived — a simple number that, paired with sales history, points to what deserves attention before it becomes a bigger problem.

What inventory aging means

Inventory age is the number of days between when a unit was received and today (or, for a discontinued item, the day it stopped being tracked). It says nothing on its own about whether a product is a problem — a well-performing seasonal item and a genuinely stuck SKU can show the exact same age.

Why retailers track it

Age is cheap to compute and available for every SKU, which makes it a useful first filter across a large catalog — sort by age, then look closer at what's both old and not selling. Tracking it regularly also reveals whether your buying is outpacing your sell-through over time.

Common aging buckets

0–30 days — new receipt
31–90 days — maturing, still within a normal window for most categories
91–180 days — aging, worth checking against sales velocity
181–365 days — significantly aged
365+ days — review recommended

Try it on one item with the free Inventory Aging Calculator.

The formula

Inventory Age (days) = Today − Date Received

Some retailers instead use days since the last sale, or the later of the two dates — the right choice depends on whether you care more about “how long have we held this” or “how long has it been dormant.”

Example

A SKU received 210 days ago, with 40 units on hand at $18 unit cost, falls in the 181–365 day bucket and represents $720 of inventory cost ($18 × 40). Whether that's a problem depends on whether it's still selling.

Financial implications

Every day an item sits unsold is a day its cost isn't available for inventory that turns. Aging analysis, weighted by cash tied up rather than SKU count, is what surfaces where that cost actually concentrates — a handful of aged, high-cost SKUs usually matter more than a long tail of aged, cheap ones.

How aging differs by product category

Fast fashion and fresh goods should treat a 60-day age as significant. Durable goods, big-ticket items, or genuinely evergreen products can carry a much longer age without concern. There is no single “correct” threshold across categories.

Markdown considerations

Age alone shouldn't set a markdown percentage — margin, remaining sales potential, and how much cash is at stake all matter. See the dead stock guide for how age combines with sales history to point toward a specific action.

How to identify aging inventory across a catalog

The math is simple for one item; doing it consistently across a few thousand SKUs — and combining it with sales velocity and margin — is what Inventory Assassin automates, ranking results by cash at stake rather than leaving you to sort a spreadsheet.