If you sell physical product, "profitable but broke" usually isn't a mystery once you look in the right place. It's inventory. Specifically, it's inventory being expensed on the wrong day — the day you bought it, instead of the day you sold it.
That one timing mistake distorts everything downstream: your monthly P&L, your gross margin by SKU, your sense of which products are actually worth reordering. Here's the actual mechanism, not just the diagnosis — and the two accounting choices that determine how bad the distortion gets.
The Mistake: Expensing Inventory When You Buy It, Not When You Sell It
Say you spend $50,000 on inventory in January. If your books record that $50,000 as an expense the moment you pay for it, January's P&L takes a $50,000 hit — even though nothing has sold yet. That inventory is sitting in a warehouse. It's an asset, not a cost.
Then March comes around and you sell through most of that stock. Revenue shows up, but the cost was already expensed two months earlier — so March's P&L looks unusually profitable, disconnected from what actually happened that month. Your cash flow, meanwhile, never lied: it went out in January, plain and simple. The P&L is the one telling a distorted story, in both directions.
The correct treatment is straightforward on paper: inventory is an asset until it sells. The cost only becomes Cost of Goods Sold — an actual expense — at the moment of sale, matched against the revenue it produced. It's the mechanic almost every generalist bookkeeper gets wrong for ecommerce clients, because it's invisible unless you're specifically checking for it.
FIFO vs. Weighted Average — the Method You Pick Changes Your Real Numbers
Getting the timing right is step one. Step two is which cost gets attached to each unit sold, and that depends on which inventory valuation method your books use.
FIFO (first-in, first-out) assumes the oldest units you bought are the first ones sold. Weighted average blends every unit currently in stock into one average cost, recalculated as new inventory arrives. A quick example makes the gap concrete:
| Purchase | Units | Cost/Unit |
|---|---|---|
| January order | 100 | $8.00 |
| March order | 100 | $10.00 |
| April: sell 120 units | FIFO COGS: $1,000 · Weighted Average COGS: $1,080 | |
Same 120 units sold, same revenue — an $80 difference in COGS, which is an $80 difference in reported gross profit, purely from a bookkeeping method choice. Scale that gap across thousands of SKUs and a full year, and it's not a rounding error anymore; it's the difference between trusting your margin numbers and guessing at them. Rising supplier costs make the gap wider. Stable costs make it nearly disappear — which is exactly why this problem hides for brands with steady input pricing and surfaces hard the first time costs move.
Neither method is "correct" in isolation. What matters is picking one, documenting it, and applying it consistently everywhere — your accounting software, your inventory management tool, and any channel-specific reporting all need to agree.
Why This Distorts Your Margin by SKU and Channel
Once COGS is being calculated inconsistently — or at the wrong time — every downstream number inherits the distortion. Contribution margin by SKU stops being reliable. So does channel profitability once you're reconciling Shopify, Amazon FBA, and wholesale through the same chart of accounts. You can end up reordering a product that looks like a winner on paper and is actually break-even, or cutting one that's quietly your best margin performer, because the COGS attached to each was never apples-to-apples.
The Fix Isn't "Hire Someone to Categorize Transactions Faster"
Faster categorization doesn't fix a timing and methodology problem — it just gets the wrong numbers into your reports sooner. The actual fix has two parts: book inventory purchases to the balance sheet as an asset, and release COGS only at the point of sale, using one inventory valuation method applied consistently. In practice, that means your inventory management system (Shopify, a dedicated inventory tool, or Amazon Seller Central) needs to sync cleanly into your accounting software — through something like A2X or Link My Books — rather than your bookkeeper hand-entering purchase totals as expenses each month.
Get that mechanism right once, and your P&L starts reflecting what's actually happening in the business, month to month, instead of lagging or leading it by however long your inventory sits on the shelf.
The Cash-Reserving Discipline: Funding Your Next Reorder Before You Need To
Correct accounting tells you the truth about your margins. It doesn't automatically protect the cash for your next purchase order. As sales revenue lands in the account, it's easy to treat all of it as spendable — but a chunk of that inflow is already spoken for: the next reorder. The discipline that actually protects cash is treating that upcoming purchase like a bill you owe yourself, and setting the amount aside as revenue comes in, before ad spend, payroll, or owner draws touch it.
Sizing that reserve isn't a guess — it comes from your inventory run rate: how many units you're moving per day or week at current velocity. Multiply that by your supplier's lead time, plus a safety buffer, and you know both when the next order needs to go out and roughly what it'll cost. Tie that number into a rolling cash forecast and "hope there's enough cash when reorder time comes" turns into a number you already know six to eight weeks out — the same runway that keeps a reorder crunch from ever becoming an emergency.
A Quick Way to Check Your Own Inventory Books
If you're not confident in more than one of these, the distortion has probably already started:
- Do you know your gross margin by SKU — not just overall?
- Do you know which inventory valuation method your books actually use right now?
- Has your COGS ever been reconciled against what physically sold in a period, not just what was purchased?
- Would a 20% swing in your landed cost change how you'd price or reorder a product?
When to Get Help
A generalist bookkeeper can categorize transactions accurately and still get inventory timing wrong, simply because it's not the mechanic most bookkeeping training covers. Ecommerce-specific accounting means multi-channel reconciliation, inventory and COGS handled correctly, and margin visibility by SKU and channel — the full picture, not just categorized transactions.
That's the core of what we do for ecommerce and DTC brands at Bindery. And if the cash-versus-profit gap this creates sounds familiar beyond just inventory timing, our post on why profitable businesses run out of cash covers the broader mechanism and the forecast that catches it early.
FAQ
Why does my ecommerce business look profitable but I never have cash?
The most common cause is inventory being expensed when it's purchased instead of when it's sold. Cash goes out the moment you buy stock, but under accrual accounting that cost shouldn't hit your P&L as COGS until the item actually sells. If your books expense it at purchase, your P&L understates profit in buying months and overstates it in selling months, while your bank account is telling the true story the whole time.
What's the difference between FIFO and weighted average inventory accounting?
FIFO (first-in, first-out) assumes the oldest units you bought are the first ones sold, so COGS reflects your earliest purchase costs. Weighted average blends all units currently in stock into a single average cost per unit, updated as new inventory comes in. When your product costs are stable, the two methods land close together. When costs are rising or volatile, they can produce meaningfully different COGS and gross margin for the exact same sales.
Should I expense inventory when I buy it or when I sell it?
When you sell it. Inventory you've purchased but haven't sold is an asset sitting on your balance sheet, not an expense on your P&L. The cost only converts to Cost of Goods Sold at the moment of sale, matched against the revenue it generated. Expensing it at purchase is the single most common inventory accounting mistake we see in ecommerce books.
How do I know if my ecommerce bookkeeping has outgrown a generalist bookkeeper?
If you can't answer your gross margin by SKU or channel, don't know which inventory valuation method your books actually use, or your COGS number has never been reconciled against what physically sold in a period, your bookkeeping is behind where your business already is. That's usually the point to bring in ecommerce-specific accounting rather than a generalist.
This article is general guidance, not personalized tax or accounting advice. Every business's inventory situation is different — talk to us about yours.