SellersCalc

Inventory math

Inventory Aging Calculator

Not how old your stock is today — how old it will be when the last unit finally sells, and how much cash rides along the way.

Age at sell-out = days in stock + units on hand ÷ daily sales. Inventory aging asks the forward-looking question: at the current sales rate, how old will this batch be when it clears? 400 units that have already sat 45 days and sell 10 a day need 40 more days, so the last unit leaves at 85 days old with $4,800 of cost tied up meanwhile. Batches projected past 180 days are drifting toward dead stock and markdown territory. Enter units, run rate, current age, and unit cost to see each batch’s trajectory before it becomes a write-off.

Inventory Aging Calculator — your numbers

Age at sell-out (days)

85

Days left to clear

40

Cash tied up

$4,800.00

Estimate only. Results reflect exactly the numbers you enter — verify against your own accounting before making pricing decisions.

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Worked examples

Healthy mover

Units on hand 400
Average daily sales 10
Days in stock so far 45
Unit cost $12.00
Age at sell-out (days) 85
Days left to clear 40
Cash tied up $4,800.00

Clears in 40 more days at 85 days old — inside a normal quarter.

Batch drifting toward dead stock

Units on hand 600
Average daily sales 3
Days in stock so far 90
Unit cost $12.00
Age at sell-out (days) 290
Days left to clear 200
Cash tied up $7,200.00

200 more days to clear: the last unit sells at 290 days old, with $7,200 parked.

Frequently asked questions

What is a good inventory aging profile?

A common target is the bulk of stock value under 90 days old, a small tail at 90–180, and close to nothing beyond 180. If this calculator projects a batch clearing past 180 days old, act now — a modest discount today beats a deep markdown in six months plus half a year of holding cost. Amazon FBA makes the threshold explicit: aged-inventory surcharges start at 181 days.

Why project age at sell-out instead of just looking at current age?

Because a 30-day-old batch can be in worse shape than a 90-day-old one. 600 units at 30 days old selling 2 a day will still be on the shelf next year, while 100 units at 90 days old selling 10 a day are gone in ten days. Current age describes the past; age at sell-out prices the decision you have to make today.

What should I do with stock that ages past 180 days?

Escalate in steps: first try a price cut of 10–20% and refreshed listings or ads, then bundle it with a fast mover, then liquidate through outlet channels or clearance marketplaces, and finally donate or dispose to stop paying storage. Each step down recovers less cash, which is exactly why catching the trajectory early — while a small discount still clears it — is worth the monthly check.

Does aging matter if my product never expires?

Yes, because the costs are financial, not just physical. Every month on the shelf costs roughly 2–2.5% of the stock’s value in capital, storage, and insurance, and even durable goods lose relevance to design changes, new competitors, and shifting demand. Expiry just adds a hard deadline; the carrying cost clock runs on everything.

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