The problem allocation solves
A carrier invoice arrives as one large total, often broken down by shipment but not by product or customer. Yet the business needs to know what shipping costs for each product, each sales channel and sometimes each customer group, so that prices, margins and promotions make sense. Allocation is the practice of assigning that total to the things that caused it.
There is no single correct method. Each choice involves a trade-off between accuracy and effort, and the best method is the one that is accurate enough to support the decision it feeds.
When allocation matters
- Setting prices. A product that is expensive to ship may need a higher price or a delivery charge, while a light one may not.
- Measuring profit by product or channel. If shipping is ignored or spread evenly, bulky products can look more profitable than they are.
- Reviewing promotions. Whether a free shipping offer is sensible depends on the shipping cost of the products it covers.
- Comparing channels. A marketplace, your own store and wholesale orders may involve different packaging, destinations and service levels.
Common methods
Equal split per order
Divide the total shipping cost by the number of orders. It is the simplest approach. It works only when orders are fairly uniform, and it penalises small, light orders while subsidising heavy ones.
Split by units or revenue
Share the total in proportion to the number of items sold or to sales value. This is easy to calculate but often poorly related to what drives carrier charges. A high-value, small item gets a large share of cost even though it is cheap to ship.
Split by weight or volume
Share the total in proportion to weight, or better, to billable weight, since that is what carriers charge for. This captures the main cost driver for most parcels. Bulky items are better reflected if you use dimensional weight and not just scale weight. Data about product dimensions is required.
Direct assignment by shipment
Where each order’s shipping charge is known, assign it straight to the products in that order. For single-item orders the result is exact. For multi-item orders, the cost is then divided between the items, commonly by weight or value.
Activity-based allocation
Break the cost into its causes, such as base rate by zone and weight, specific surcharges, packaging and labor, and assign each to the products or channels that trigger it. It is the most accurate and the most demanding approach, and it usually relies on shipping software or data analysis to produce results.
A worked example
A store spends 1,200 on shipping in a month across 400 orders. Product X is a light item with 300 orders, and Product Y is a heavy item with 100 orders. Looking at shipment-level charges, X orders cost 2.00 each and Y orders cost 6.00 each.
Check: 300 x 2.00 = 600 and 100 x 6.00 = 600, which together give 1,200.
An equal split per order gives 1,200 / 400 = 3.00 for every order. Compared with the actual figures:
- X is charged 3.00 instead of 2.00, so its cost is overstated by 1.00 per order.
- Y is charged 3.00 instead of 6.00, so its cost is understated by 3.00 per order.
The store might conclude that Y is more profitable than it is, and keep its delivery charge low or its price unchanged. The numbers are invented for illustration, but the pattern, in which averaging favors heavy products at the expense of light ones, is common.
Allocating to customers and channels
The same logic applies to groups of customers. Local customers cost less to serve than distant ones, and customers who return many orders cost more. Methods used here include:
- allocating by delivery zone, using the carrier’s zone charts
- allocating by sales channel, using each channel’s own order and shipment records
- adding return costs to the customer segments that generate them, which draws on data about return rates and prepaid return labels
- treating international orders separately, since duties, brokerage and different carriers change the cost structure
Practical guidance
- Start with the decision. If the aim is a checkout shipping charge, the allocation needs to track what customers see: destination and weight. If it is product profitability, weight and volume probably matter most.
- Use real shipment data where it exists. Allocation by estimation is a fallback when records are missing.
- Keep the method stable. Switching methods from month to month makes comparisons meaningless. Change only when you have a reason, and record that you did.
- Include more than the carrier bill. Packaging and labor can be allocated by the same logic; the calculation of cost per parcel shows what belongs.
- Be aware of shared costs. Fuel and some other surcharges apply across shipments, so allocate them in proportion to the base charges they follow.
- Review periodically. A change of carrier, a rate rise or a new packaging format can change the right split.
Fairness and limits
Fairness here means that costs follow causes as closely as practical. Perfect fairness is not achievable, and an allocation is a model, not a fact. If a method hides an important difference, such as heavy items looking cheap to ship, refine it. If a more elaborate method would not change any decision, the simpler one is sufficient.