An ecommerce shop’s busiest holiday season could also be its least profitable.
Ecommerce businesses face direct variable costs with every order. Two orders with the same revenue and gross profit might produce different bottom-line profits.
Without an understanding of those costs, an entrepreneur could think the business is succeeding when it’s actually failing.
Holiday Shipping
Take shipping and fulfillment, for example. Merchants face two cost increases this 2026 holiday season.
- The U.S. Postal Service raised its shipping rates. It increased by 8% Priority Mail Express, Priority Mail, Ground Advantage, and Parcel Select, effective April 26 through January 17, 2027.
- Fulfillment by Amazon announced new peak fulfillment fees from October 15 through January 14, 2027. Those peak fees will average roughly 32 cents per unit over non-peak rates. FBA is also adding a 3.5% fuel and logistics surcharge.
Each order delivered via USPS or FBA during those periods contributes a little less.
Contribution Margin
“Contribution margin” is a helpful indicator for tracking and modeling this sort of change. “Gross margin” is revenue less the cost of goods sold. Contribution margin goes further to include all variable costs:
- Cost of goods sold,
- Packaging and pick-and-pack fees,
- Outbound shipping,
- Payment processing,
- Expected returns,
- Marketplace commissions,
- Affiliate fees,
- Performance advertising.
Thus “contribution” describes what is left to contribute toward fixed expenses such as salaries, software, insurance, and rent.
Contribution margin = Revenue − Total variable costs
Anything remaining — contribution margin less fixed expenses — is operating profit.
Order Economics
Imagine a $100 ecommerce order.
The product costs $40, payment processing is $3, fulfillment and shipping total $12, expected returns account for $5, and performance advertising runs $15.
The order produces a $25 contribution margin before the USPS rate increase. An 8% increase adds 56 cents to the order cost, reducing contribution margin to $24.44.
| Order Economics | Original | After 8% USPS Increase |
|---|---|---|
| Revenue | $100.00 | $100.00 |
| Product cost | -$40.00 | -$40.00 |
| Payment processing | -$3.00 | -$3.00 |
| Fulfillment | -$5.00 | -$5.00 |
| Shipping | -$7.00 | -$7.56 |
| Expected returns | -$5.00 | -$5.00 |
| Performance advertising | -$15.00 | -$15.00 |
| Contribution margin | $25.00 | $24.44 |
| Contribution margin % | 25.0% | 24.4% |
The $0.56 difference on a single order is small. Across 10,000 holiday orders, however, it represents $5,600 less contribution toward salaries, software, and rent.
The same exercise can model changes in FBA fees, advertising costs, return rates, discounts, or other variable expenses.
| FBA Order Economics | Non-peak | Holiday Peak |
|---|---|---|
| Revenue | $100.00 | $100.00 |
| Product cost | -$40.00 | -$40.00 |
| Amazon referral fee, 15% | -$15.00 | -$15.00 |
| FBA fulfillment fee | -$5.00 | -$5.32 |
| Fuel and logistics surcharge | -$0.18 | -$0.19 |
| Expected returns | -$5.00 | -$5.00 |
| Amazon advertising | -$15.00 | -$15.00 |
| Contribution margin | $19.82 | $19.49 |
| Contribution margin % | 19.8% | 19.5% |
Operating Decisions
Contribution margin is useful as a key performance indicator and a guide to decision-making.
Consider:
- Discounts. A merchant can estimate how a 10%, 15%, or 20% discount would affect contribution before launching a promotion. The calculation can show whether higher sales volume would offset the lower per-order contribution.
- Acquisition. Contribution margin can help determine how much a company can spend to acquire a customer. If an order contributes $25 from repeat customers, the marketing team can model acceptable advertising expense to acquire new ones.
- Fulfillment options. A merchant can compare contribution margins from free shipping, customer-paid shipping, different carriers, FBA, and other fulfillment arrangements. A cheaper option may not produce better margins if it adds handling expense or increases returns.
- Channel mix. The same product sold for the same price can produce different contribution margins across a merchant’s website, Amazon, or any other source. Tracking contribution by channel can show where sales are most profitable.
In short, peak-season success is more than sales. Contribution margin shows whether those extra orders actually increased profits.
