Inventory and Cash Flow: Avoid the Stockout and Overstock Trap

You can be profitable on paper and still go broke. It happens to marketplace sellers constantly: the product makes money per unit, sales are growing, and then there's no cash to reorder. Inventory is where profit and cash flow pull in opposite directions, and managing that tension is what separates sellers who scale from sellers who stall.

Why profit isn't cash

Profit is earned when you sell. Cash is gone when you buy inventory, weeks or months earlier. Between paying your supplier and getting paid by the marketplace sits a gap: production time, shipping, customs, the marketplace's payout schedule, and the days your stock sits before it sells. Every unit on a shelf is cash you've already spent and haven't recovered.

Growing makes this worse, not better. Faster sales mean reordering sooner and bigger, which means more cash tied up at once. This is why scaling sellers feel poorer the faster they grow.

The two traps

• Stockout. You run out, your listing loses ranking and reviews momentum, and competitors take the sales you trained the algorithm to send you. Recovering a ranking is far more expensive than holding a little safety stock.
• Overstock. You buy too much, cash freezes in unsold units, storage fees climb (especially with FBA long-term storage), and you end up discounting just to free up capital.

Both are failures of timing, not just quantity. The goal isn't "more" or "less" inventory. It's the right amount arriving at the right time.

Know your reorder point

The reorder point is simple to state and easy to ignore: order when your stock will last only as long as it takes new stock to arrive (plus a safety buffer). You need three numbers:

• Daily sales rate. Units per day, honestly averaged.
• Lead time. Order to sellable, including production, shipping, customs, check-in.
• Safety stock. A buffer for demand spikes and lead-time slips.

Reorder point ≈ (daily sales × lead time) + safety stock. Hit that number, place the order. This one habit prevents most stockouts.

Protect your working capital

Cash is the constraint, so treat it like one:

• Don't sink all your capital into one big order for a discount you can't afford to have frozen.
• Watch cash conversion, the time from paying the supplier to getting paid, and shorten it where you can (faster shipping mode, negotiated supplier terms, quicker marketplace payouts).
• Keep a reserve. A profitable business with no cash buffer is one supplier delay away from a stockout.

Read the signals before they hurt

Inventory pressure shows up in your numbers before it shows up in your bank account. Days of cover dropping, a reorder point approaching, capital concentration in slow movers. These are early warnings. Merckit's unit economics tables surface inventory cash-pressure signals alongside per-SKU margin, so you see which products are about to need cash and which are quietly tying it up. Pair it with a pricing strategy that protects margin and the margin model so growth doesn't outrun your cash.

FAQ

Why am I profitable but always short on cash?

Because profit is booked at sale and cash leaves at purchase. The gap (production, shipping, payout timing, days in stock) ties up your money, and faster growth widens it.

How do I calculate when to reorder?

Reorder point ≈ (daily sales rate × lead time) + safety stock. When stock hits that level, order, so new units arrive before you run out.

Is it worse to stock out or overstock?

Both hurt. Stockouts cost ranking and momentum that's expensive to rebuild; overstock freezes cash and racks up storage fees. Right quantity at the right time beats either extreme.

How much safety stock should I hold?

Enough to cover normal demand spikes and typical lead-time slippage, but not so much that capital freezes. Base it on your demand variability and how reliable your supplier's lead time is.