Chapter 2 Cost Calculation
Purchase is not only about placing orders with vendors. Once purchased products are received into stock, they may also affect product cost, inventory valuation, and later sales margin. For companies using Odoo Inventory and Accounting, purchase cost logic should be understood before go-live, otherwise product margin and stock value can easily become confusing.
This chapter explains the basic cost calculation idea around purchase receipts, especially the average cost method.
Receipt And Cost Update
If a product uses the average cost method, Odoo updates the product cost after purchase receipt according to the value of the incoming goods and the existing inventory value.
The simplified formula is:
Average cost = (Purchase price x Purchased quantity + Previous average cost x Existing stock quantity) / Stock quantity after receipt
Example:
Existing stock: 10 units
Previous average cost: 20
New purchase: 5 units
Purchase price: 26
New average cost = (26 x 5 + 20 x 10) / 15 = 22
This means the cost does not simply become the latest purchase price. It becomes a weighted average of existing stock and incoming stock.
Stock Valuation Layers
Although the formula above is useful for understanding, Odoo does not rely only on one visible formula field in real inventory accounting. Modern Odoo versions use stock valuation layers to record inventory value changes caused by receipts, deliveries, returns, and adjustments.
Stock valuation layers help trace:
- Which receipt brought value into stock.
- Which delivery consumed stock value.
- How inventory value changed over time.
- Why product cost or margin changed.
- How accounting entries were generated when automated valuation is enabled.
For implementation, this means users should not manually change cost without understanding the downstream impact. Product cost, receipt price, vendor bills, landed costs, and inventory valuation can all affect management reports.
Cost Method Matters
Different product categories can use different costing methods. Common methods include:
| Cost Method | Meaning | Purchase Impact |
|---|---|---|
| Standard Price | Cost is maintained manually or by controlled update | Purchase receipt usually does not change product cost automatically |
| Average Cost | Cost updates according to weighted average after receipt | Purchase price and received quantity affect product cost |
| FIFO | Outgoing value follows first-in-first-out valuation layers | Purchase receipts create cost layers consumed later |
The cost method is usually configured on the product category. It should be decided before large-scale transactions, because changing cost method after go-live can be sensitive.
Purchase Price And Vendor Bill
The purchase order price is the expected purchasing price. The vendor bill is the financial document from the supplier. In many simple flows, they are the same. In real projects, differences may appear:
- Vendor changes final price.
- Freight or landed cost must be allocated.
- Discount is applied on the bill.
- Currency exchange rate changes.
- Quantity received differs from quantity billed.
If the company needs strict inventory valuation, purchase order, receipt, and vendor bill should be reviewed together.
Implementation Advice
Before going live, confirm these points with finance and warehouse:
| Question | Why It Matters |
|---|---|
| Which products need inventory valuation? | Not every service or consumable needs the same treatment |
| Which cost method should each category use? | It affects product cost and margin |
| Is valuation manual or automated? | Automated valuation creates accounting entries from stock moves |
| Are landed costs required? | Freight, duty, and other costs may need allocation |
| Who can change product cost? | Cost changes affect reports and decisions |
For a beginner implementation, use a small sample of products to test purchase receipt, vendor bill, and stock valuation before importing a large product catalog.
This chapter explained how purchase receipts affect product cost and why cost method design matters. The next part moves into warehouse management, where receipts, locations, transfers, batches, barcode, and replenishment are handled in more detail.