Why Amazon Sales Can Grow While Your Profit Shrinks

Most solo sellers have lived some version of this month: the sales chart in Seller Central is the best it has ever been, and the bank balance looks almost exactly like it did last quarter. Nothing is broken. No single report is red. And yet the business is working harder to keep less.

This is not bad luck. Revenue and profit are driven by different numbers, and the numbers that drive profit are scattered across places that rarely show up on the same screen. Below are the five leaks we see most often, followed by a monthly check you can run in under an hour.

Revenue is one number. Profit is a stack.

Revenue is a single line: units times price. Profit is what is left after a stack of deductions, and every layer of that stack can move independently:

• Amazon referral fees, charged as a percentage of the sale price.
• FBA fulfillment fees, charged per unit and tied to size and weight tiers.
• Storage and inventory-related fees, which change with season and stock levels.
• Advertising spend, usually the most volatile layer.
• Refunds, returns and reimbursements.
• Cost of goods, freight, duties and prep, which sit outside Amazon entirely.

When sales grow, several of these layers grow with them. Some grow faster. That is how a month with record revenue can deliver a smaller profit than a quieter month a year earlier.

Leak 1: advertising grows faster than sales

The most common pattern is simple. To defend rank, a seller raises bids or budgets. Sales rise, but the incremental sales cost more than the ones before. If you only look at ACoS on the ads console, you can miss that total ad spend is now a larger slice of total revenue. That relationship is what TACoS measures, and we cover the difference in ACoS vs TACoS vs net margin.

Illustrative example. A seller does $18,000 in a month with $2,200 of ad spend. The next month they push to $24,000 with $4,600 of ad spend. Revenue grew 33%. Ad spend grew 109%. Unless margin per unit is generous, the extra $6,000 of sales may have contributed almost nothing to profit.

Leak 2: fees that scale per unit

Fulfillment fees are charged per unit, not per dollar. If growth comes from a lower-priced variant or a discount, the fee takes a bigger share of each sale. Amazon publishes its current fee schedule on its Selling on Amazon pricing page, and fee tables are updated periodically, so it is worth rechecking your per-unit fee whenever Amazon announces changes rather than relying on last year's spreadsheet.

Leak 3: discounts that buy volume, not margin

Coupons, deals and price cuts can lift unit volume quickly. The question is not whether they increase sales; they usually do. The question is what each discounted unit contributes after fees and ads. A 15% coupon on a product with a 25% contribution margin removes most of the profit from that unit.

Leak 4: cash moving into inventory

Growth needs stock, and stock needs cash before it earns anything. A business can be profitable on paper while the bank balance shrinks because money is sitting in a container on the water. That is a cash-flow issue rather than a profit issue, but it feels identical from the founder's chair. We cover reorder timing in inventory cover, reorder timing and cash flow.

Leak 5: costs that never reach the dashboard

Freight, duties, prep, packaging, software subscriptions and bookkeeping often live in a separate spreadsheet, or nowhere. If your profit figure does not include them, it is overstated every single month. See what your Amazon profit calculation is missing for a full checklist.

Why nobody notices

Each leak is small on its own. A few points of extra ad spend here, a slightly higher fee there, a coupon that ran a week too long. None of them shows up as a crisis in any single report, so nothing ever triggers a decision. The damage is in the sum.

That is the real problem: not a lack of data, but a lack of one place where the data turns into a decision.

A monthly profit check in five steps

Set aside an hour on the first business day of each month. You need your settlement or payment report, your ad console totals and your landed cost per unit.

1. Write down net revenue for the month after refunds.
2. Subtract every Amazon fee from the settlement report, not from an estimate.
3. Subtract total ad spend across all campaign types.
4. Subtract landed cost of goods sold, including freight and duties per unit.
5. Subtract fixed costs such as software and bookkeeping.

Divide what is left by net revenue. That is your net margin. Compare it to the last three months, then ask one question for each layer: which one moved the most? That layer gets your attention this month.

If your net margin fell while revenue rose, start with advertising. In most small catalogs it is the layer that moves fastest and responds fastest to a decision.

What to do with the answer

The point of the check is to end with a specific decision, not a feeling. Examples of decisions that follow directly from it:

• Cap the daily budget of one campaign that has grown faster than its sales.
• Raise a price by a small, tested amount on a variant whose fees have risen.
• End a coupon that is buying volume at a loss.
• Move a reorder date so cash is not tied up earlier than necessary.

If you want a recurring format for this, our weekly review template turns the same numbers into a short list of decisions every Monday.

How Sollo Central approaches it

Sollo Central keeps these layers in one daily profit view, with guardrails you set, such as a margin floor and a monthly ad ceiling. When a layer moves, it proposes a specific change with the numbers behind it, and nothing is executed on Amazon until you approve it. The goal is the same as the manual check above: fewer surprises, and decisions you understand.