---
title: Add Stock and Calculate an Average Cost
description: Record new stock and let WooCommerce work out a new average cost, so cost of goods stays accurate when purchase prices change.
url: "https://wpfactory.com/docs/add-stock-average-cost/"
updated: "2026-09-27"
category: How to
---

# Add Stock and Calculate an Average Cost

The Add stock feature works out a new average cost for a product each time you receive more stock, so your cost of goods stays accurate when you buy the same product at different prices. It is a free feature of [Cost of Goods: Product Cost & Profit Calculator for WooCommerce](https://wpfactory.com/item/cost-of-goods-for-woocommerce/).

![Add stock meta box on the product edit screen with the Stock and Cost inputs](https://wpfactory.com/wp-content/uploads/add-stock-average-cost-1.png)

## What it does

Instead of overwriting the cost when you restock, Add stock blends the old stock and cost with the new stock and cost to produce a weighted average. The calculation is:

`( %stock_prev% * %cost_prev% + %stock% * %cost% ) / %stock_now%`

So if you hold 10 units bought at 4.00 and receive 10 more at 6.00, the new average cost becomes 5.00. The product's cost field is updated to that figure, and WooCommerce stock is increased by the amount you added.

## Turn it on

1. Go to **WPFactory > Cost of Goods** (also reachable at **WooCommerce > Settings > Cost of Goods**).
2. On the **Products** sub-tab, find the **Add stock** group and tick **Enable "Add stock" feature**.
3. Click **Save changes**.

The feature relies on WooCommerce stock management, so enable **Manage stock** on the products where you want to use it.

## Add stock on a product

1. Open a product for editing.
2. In the **Add stock** meta box, enter the quantity you received in **Stock** and the price you paid per unit in **Cost**.
3. Update the product. The cost field is recalculated to the new weighted average and the stock is increased.

## Options reference

| Label | Option ID | Default | Free/Pro |
| --- | --- | --- | --- |
| Add stock | `alg_wc_cog_products_add_stock` | No | Free |
| Format decimals | `alg_wc_cog_products_add_stock_format_decimals` | No | Free |
| Cost calculation expression | `alg_wc_cog_products_add_stock_cost_calculation` | `( %stock_prev% * %cost_prev% + %stock% * %cost% ) / %stock_now%` | Pro |
| Empty cost field | `alg_wc_cog_products_add_stock_empty_cost_action` | Do nothing | Pro |
| History date format | `alg_wc_cog_products_add_stock_history_date_format` | `Y-m-d` | Free |
| History date order | `alg_wc_cog_products_add_stock_history_date_order` | Descending | Free |
| Negative stock | `alg_wc_cog_products_add_stock_negative_stock` | No | Free |

## Free and Pro

The Add stock meta box and its average-cost calculation are free. The Pro version adds two controls: **Cost calculation expression**, which lets you rewrite the averaging formula using the `%stock_prev%`, `%cost_prev%`, `%stock%` and `%stock_now%` placeholders, and **Empty cost field**, which decides what happens when the cost you enter is blank (for example, keep the current cost or treat it as zero).

## Get more from Cost of Goods

Add stock with automatic average cost is free. [Cost of Goods: Product Cost & Profit Calculator for WooCommerce](https://wpfactory.com/item/cost-of-goods-for-woocommerce/) Pro adds a custom cost expression and empty-cost handling here, plus cost and profit in WooCommerce Analytics and order emails. [See what Pro unlocks](https://wpfactory.com/item/cost-of-goods-for-woocommerce/).

Related articles

- [Add Extra Order Costs: All Orders, Per Order, and From Meta](https://wpfactory.com/docs/extra-order-costs/)
- [Add Extra Shipping Method and Shipping Class Costs](https://wpfactory.com/docs/extra-shipping-costs/)
- [Add Payment Gateway Costs to Order Profit](https://wpfactory.com/docs/manage-payment-gateways/)
- [Add “Add Stock” Fields to Product Quick Edit and Bulk Edit](https://wpfactory.com/docs/add-stock-fields/)
- [Add a Cost Field to Product Quick Edit and Bulk Edit](https://wpfactory.com/docs/add-cost-field/)