01
How the moving weighted average works
Add purchase cost to the inventory value on hand, then divide by the new unit total.
InventoryFREE · NO SIGNUP
Weighted Average Perpetual Inventory System Calculator
Process purchases and issues in order to recalculate moving weighted-average cost, cost of goods issued, and ending inventory.
FREE TO USEA LOOK ATLAS TOOL
01 USE IT NOW02 NO ACCOUNT03 FIELD NOTES BELOW
WORKING INPUTS
Keep the inventory timeline in sequence.
LIVE RESULT
Ending inventory value
$921.21Perpetual moving-average result for the entered event sequence; currency and cost scope must remain consistent.ENDING UNITS80
COST OF GOODS ISSUED$1,198.79
AVERAGE AFTER PURCHASE 1$10.67
AVERAGE AFTER PURCHASE 2$11.52
15
SEQUENCE CHANGES THE COST
Recalculate only when inventory is purchased
A perpetual weighted-average system updates unit cost after each purchase. Issues reduce units and value at the moving average already in force.
WORKING VIEW
$921.21 ENDING VALUE100 @ $10 · 50 @ $12
METHODending units × the latest moving weighted-average unit cost
WORKING NOTE80 ending units after two purchase-and-issue cycles
INPUTS → CLEAR OUTPUT
THE FIELD NOTES
Quick answer above. Better decisions below.
Use the result now, then read the practical notes for assumptions, examples, limitations, and the choices behind it.
100 @ $10 · 50 @ $12$921.21 ENDING VALUE
80 ending units after two purchase-and-issue cycles
02
Do not substitute the periodic method
Periodic weighted average pools the whole period before assigning cost.
03
Validate every issue against units available
The calculator stops if an issue would drive inventory below zero at that point in the timeline.
04
Keep the calculation tied to the event ledger
Reconcile entered quantities and costs to receiving and issue records before using the output.
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How the moving weighted average works
Add purchase cost to the inventory value on hand, then divide by the new unit total.
Carry that average through the next issue and recalculate only when another purchase arrives.
Do not substitute the periodic method
Periodic weighted average pools the whole period before assigning cost.
Perpetual moving average respects the event sequence, so the two methods can produce different COGS and ending inventory.
Validate every issue against units available
The calculator stops if an issue would drive inventory below zero at that point in the timeline.
Use consistent cost scope and currency across beginning inventory and purchases.
Keep the calculation tied to the event ledger
Reconcile entered quantities and costs to receiving and issue records before using the output.
Rounding and accounting policy should be applied consistently in the books of record.
Questions, answered.
How is perpetual weighted-average cost calculated?
After each purchase, divide the inventory value on hand plus purchase cost by the total units now available. Issues use that current moving average.
When does the moving average change?
It changes after a purchase. A sale or issue reduces units and inventory value at the current average but does not create a new unit cost.
Is this the same as periodic weighted average?
No. Periodic averaging pools the period; perpetual averaging follows each purchase and issue in sequence.
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