6 Reasons Your Gross Margin Moved When Your Business Did Not
Sam's List Editorial | 2026-09-02
You sold roughly the same things at roughly the same prices to roughly the same customers.
Gross margin came in six points lower.
Nobody changed a price. No vendor raised a rate. The number moved anyway, and the meeting where you try to explain it turns into forty minutes of guessing. Here is the thing worth knowing: when gross margin moves and the business did not, the cause is usually a coding or cutoff decision rather than an operating event.
Which is good news. Coding decisions are fixable. Here are the six that account for most of it, and the smallest test for each.
| What moved | Where to look first |
|---|---|
| Freight, merchant fees, shipping supplies | Which account the bill hit this month vs. last |
| Purchase and sale in different months | Inventory cutoff at period end |
| Vendor rebates and volume discounts | Whether they landed in other income |
| Labor allocation | Who moved between delivery and overhead |
| Returns, refunds, chargebacks | Whether the reversal hit revenue or expense |
| Shrink, spoilage, write-offs | Whether it is recorded monthly or in a quarterly lump |
1. Freight and Fees That Drift Between COGS and Operating Expense
Merchant processing fees, shipping supplies, and third-party fulfillment charges all sit on the boundary. There is a defensible argument for putting each of them in cost of goods sold, and a defensible argument for operating expense.
Freight-in is different, and it is worth separating out. For a taxpayer required to maintain inventories, Treasury Regulation 1.471-3(b) requires transportation and other charges incurred in acquiring possession of the goods to be added to the invoice price, and resellers subject to section 263A capitalize more than that. The classification choice only exists if you qualify for the small business exemption under section 471(c), which uses the section 448(c) gross receipts test.
The problem is not which one you pick. The problem is picking differently in different months because a different person coded the bill.
A business doing $400,000 a month with 3% in merchant fees moves gross margin by three full points depending on where those $12,000 land. Nothing about the business changed. The classification did.
The test: pull the same vendor's bills for the last six months and check whether they all hit the same account. If they did not, you have found part of the swing.
2. Timing, Which Is Really a Cutoff Problem
You bought inventory in March. You sold it in April. Under accrual accounting, the cost belongs in April with the revenue. A small business electing out of inventory accounting under section 471(c) may be permitted to follow its book method instead, so confirm which regime you are in before calling this an error.
If the purchase was expensed to COGS on receipt instead of capitalized to inventory, March eats a cost it did not earn and April looks better than it was. Do that with a large order and you have manufactured a two-month margin swing out of a purchasing decision.
The same thing happens in reverse with a vendor invoice that arrives late and gets recorded in the month it was received rather than the month the goods were sold.
The test: compare inventory on the balance sheet at each month end to what was actually in the warehouse. If the book number does not move when the physical count does, cutoff is not being enforced.
3. Rebates and Volume Discounts Booked as Income
A supplier sends a $9,000 rebate check for hitting a volume tier. Somebody books it to other income, because that is what a check looks like.
Economically it is a reduction in what you paid for the goods. Booked as income, it leaves cost of goods sold overstated and gross margin understated, then quietly inflates the bottom line somewhere below the gross profit line. Timing depends on the rebate. A sales-based chargeback reduces cost of goods sold in the period, while a volume-tier rebate treated as a purchase price reduction reduces the cost of the goods and shows up when those goods sell.
The distortion runs both directions over time, and it makes year-over-year margin comparisons useless in exactly the periods you most want to compare.
The test: search other income for anything from a supplier. Most vendor money is a purchase price reduction rather than income, though consideration that reimburses a specific incremental identifiable cost or pays for a distinct good or service is treated differently under ASC 705-20.
4. Labor Allocation Nobody Updates
In service businesses this one is often the largest, and it is the hardest to see.
You have a person who spends most of their time on client delivery and some of it on internal work. Somebody decided at some point that they were 70% cost of sales and 30% overhead. Then the mix changed and the split did not, because the split lives in a payroll mapping that gets touched once a year.
Now scale that across a team. A five-point shift in how a $60,000 monthly payroll is allocated moves $3,000 across the gross profit line every month, on autopilot, until someone notices.
The test: ask three people what percentage of their time went to delivery last month, then compare their answers to the allocation in the payroll mapping. If those two numbers have never been compared, they are wrong.
5. Returns, Refunds, and Chargebacks That Land in Two Different Places
A return has two sides. Revenue reverses and the cost of the returned item reverses.
In practice one side often gets recorded and the other does not, or they land in different months, or the refund gets coded to an expense account instead of contra-revenue because it went out as a payment rather than a credit memo.
Chargebacks are worse, because the processor's deduction shows up as a net settlement amount and the underlying sale never gets unwound at all.
The test: take last month's total refunds and confirm that both revenue and cost of goods sold moved. If only one did, gross margin is carrying the difference.
6. Shrink and Write-Offs Recorded in a Lump
Inventory disappears continuously. Spoilage, damage, theft, obsolescence, samples that never came back.
If it is only recognized when someone does a physical count, the entire quarter's loss lands in one month. That month looks catastrophic and the two before it looked better than they were.
Nothing about the business changed in any of the three months. The recognition schedule did.
The test: look at whether your write-off account has entries in every month or only in March, June, September, and December.
When Gross Margin Moved: Fix the Policy, Not the Dashboard
Every cause above is a decision that was made inconsistently. The correction is boring:
- Write down what belongs in cost of goods sold. Name the accounts. Name the edge cases: freight-in, merchant fees, fulfillment, delivery labor, rebates. One page.
- Put cutoff on the close checklist. Inventory tied to a count, accruals for goods received without an invoice, refunds recorded on both sides.
- Re-examine labor allocation quarterly, not annually.
- Estimate shrink monthly and true it up at the count, rather than taking the hit all at once.
- Re-run the last twelve months under the written policy so your history is comparable to your future.
Step five is the one people skip, and it is the one that makes the policy worth having. A consistent number going forward, sitting on top of an inconsistent history, still cannot answer the question of whether margin is actually improving.
When to Bring In Help on a Gross Margin That Moved
If the swings are large enough that you distrust the monthly close, this is not a bookkeeping data-entry problem. It is a policy and close-process problem, and it usually needs someone who does financial operations rather than transaction processing.
Iota Finance is a firm founded in 2022 working with SMB owners, venture-backed startups, and real estate investors, offering bookkeeping through fractional CFO work. Iota Finance has 14 verified client reviews on Sam's List as of 2026-08-31. Each review is submitted by an individual who identifies as a client of the firm and rates it on communication, subject-matter knowledge, and overall satisfaction. Reviews reflect those individual experiences, do not represent an endorsement by Sam's List, and are not indicative of future results.
What engaging a firm does not do: it does not make your margin better. Cleaning up classification often moves the reported number, sometimes worse and sometimes better, because the errors run in both directions. What you get is a number you can act on, and a longer close for the first few months while the policy gets applied.
Two questions to ask any firm before you hire them for this. Can they show you a written COGS policy they built for another client? And will they restate your prior periods, or only fix it going forward?
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Frequently Asked Questions
Why did my gross margin change when my prices and costs did not? Almost always a classification or cutoff issue rather than an operating one. The most common causes are freight and merchant fees moving between cost of goods sold and operating expense, inventory purchased in one month and sold in another without proper cutoff, and labor allocations that no longer match how people actually spend their time.
Should merchant processing fees be in cost of goods sold? Either treatment can be defended, and the choice matters less than consistency. Many retail and ecommerce businesses put them in cost of goods sold because they scale directly with sales. Pick one, write it down, and apply it to every period including the ones already closed.
How often should I review labor allocation between COGS and overhead? Quarterly is a reasonable cadence for most small businesses, and any time someone's role materially changes. Where review happens only once a year, allocations tend to drift a long way from reality before anyone notices.
Is a big one-month margin drop always a real problem? No. Check first whether the month absorbed something that accumulated over a longer period, such as a physical inventory adjustment, a quarterly write-off, or a late vendor invoice covering several months. A recognition-timing artifact and an actual margin decline require completely different responses.
About the author: Kimberly Green is the cofounder of Sam's List, where business owners and high earners find vetted CPAs, financial advisors, and fractional CFOs. She's met one-on-one with 400+ financial professionals and writes from the real data behind thousands of client-advisor matches. Ask her anything about finding an accountant - she's heard it all, including the questions people are afraid to ask.