A freight bill is not one line
The carrier base rate is only the starting point. A zone surcharge reflects distance. Fuel is a percentage applied to the transport charge. Residential and other accessorial fees are charged per package. Packaging is your own cost, but it belongs in the same per-order view because it is incurred for the same shipment.
Splitting the bill this way shows which line is actually driving cost. A carrier discount that looks generous on the base rate can be diluted by fuel and residential fees if those are not discounted.
The order of operations changes the number
This model applies the discount to base plus zone, then calculates fuel on the discounted transport charge, then adds residential and packaging. That mirrors a common carrier structure: negotiated discounts apply to transportation, while fuel and accessorials follow their own rules.
If your contract discounts fuel or waives residential fees, adjust those inputs rather than applying a second discount. Applying the discount to the final total would understate the cost when surcharges are not discountable.
Worked example
Base $7.50, zone $1.20, fuel 6%, no residential surcharge, packaging $1.20, discount 10%, two units per order and AOV $65. Transport before discount is $8.70; the discount saves $0.87; discounted transport is $7.83; fuel is $0.47; carrier cost is $8.30; packaging brings the per-order cost to $9.50.
Per unit, that is $4.75. As a share of AOV, shipping is 14.6%. At 500 orders a month, the model produces $4,749.90 of shipping spend. Each of those numbers answers a different question: unit economics, pricing headroom and cash planning.
Per unit and percent of AOV
Per-unit shipping is useful when a product is sold in multi-packs or when you compare a single-item order with a bundle. Percent of AOV is useful for free-shipping thresholds and pricing: a 15% shipping share leaves less room for product cost, fees and ads than a 7% share.
If shipping exceeds AOV, the calculator flags it. That is not automatically impossible — a heavy, low-price item can cost more to ship than it generates in merchandise revenue — but it means the order needs a higher price, a shipping charge or a different fulfillment model.
Where the model stops
The calculator uses one package and one average order. Multi-package shipments, dimensional-weight adjustments, address corrections, returns, duties and carrier minimums need separate treatment. It also does not know your zone table, so the surcharge is an input rather than a lookup.
Use the dimensional weight calculator to check whether the package will be billed at actual or volumetric weight. Use the free-shipping threshold calculator to see how much shipping cost a threshold can absorb. Use the landed cost calculator for the goods before they reach the warehouse.
How to use the result
Compare carriers with the same order profile and the same assumptions, not with headline base rates. Then test the result against a lower discount or a higher fuel rate to see how much margin the contract really protects.
If the per-order cost is too high for the product, change one variable at a time: packaging, units per order, carrier service or price. The model is a planning tool, not a negotiation; confirm final charges on the carrier invoice.