Inventory Planning
Getting inventory right is the difference between profitable growth and cash trapped in boxes on a warehouse shelf. Too little and you stock out. Too much and your working capital evaporates.
Inventory planning is the process of determining how much stock to order, when to reorder, and where to hold it. For hardware founders, it is one of the most consequential and least intuitive parts of running a product business. Unlike software, where scaling costs are near-zero, physical products tie up real cash in every unit sitting on a shelf. Every extra week of inventory is capital you cannot spend on marketing, new product development, or simply keeping the lights on.
The fundamental tension: order too little and you stock out — losing sales today and potentially losing customers permanently. Order too much and your cash is trapped in inventory — earning zero return and costing you storage fees, insurance, and the risk of obsolescence. Good inventory planning is not about being right every time. It is about making the cost of being wrong as small as possible.
Lead time is the total calendar time from placing a PO with your factory to having finished goods available for sale on your shelf. This includes: factory production time (4–8 weeks typical), quality inspection and rework buffer (1–2 weeks), ocean freight transit (4–5 weeks to US West Coast, 5–6 weeks to East Coast), customs clearance (1–2 weeks), and inland transportation to your warehouse (3–7 days). Total typical lead time from PO to shelf: 10–16 weeks. Plan your reorder trigger accordingly.
Safety stock is the buffer inventory you hold to protect against variability — a late shipment, a quality hold, a sudden sales spike. The simplest formula: safety stock = (max daily sales × max lead time in days) − (average daily sales × average lead time in days). This gives you enough buffer for the worst reasonable case. For a first product with no sales history, start with 4–6 weeks of safety stock and adjust with data.
The reorder point is the inventory level that triggers a new PO. Calculate it as: reorder point = (average daily sales × lead time in days) + safety stock. When your inventory hits this number, you place the next order. If you wait until inventory is lower, your safety stock runs out before the new shipment arrives. Set the reorder point and automate the check — do not rely on noticing that stock is low.
EOQ (Economic Order Quantity) balances ordering cost against holding cost. The formula: EOQ = √(2DS/H) where D = annual demand, S = cost per order placed (your time, freight setup, customs brokerage), H = annual holding cost per unit (warehouse, insurance, cost of capital). EOQ gives you the mathematically optimal order size. It is a starting point, not a rule — adjust for MOQs, container efficiency, and cash constraints.
Inventory planning mistakes that kill cash flow
Planning lead time based on the best case
Your factory says 4 weeks. In reality: 4 weeks production + 2 weeks delay + 5 weeks ocean + 1 week customs = 12 weeks. Always pad lead times by 30–50% until you have a track record.
Ordering too much because the unit price is lower at higher volume
A 15% unit cost saving on 2x inventory means you tied up 2x cash to save 15%. If that cash could have funded marketing at 3:1 ROAS, you lost money. Calculate the opportunity cost of capital.
No plan for slow-moving or dead stock
Every product line has slower SKUs. If you do not have a liquidation plan (discount, bundle, write-off), dead stock accumulates and consumes warehouse space, insurance, and mental energy indefinitely.
Treating inventory value as if it equals cash
Inventory on a balance sheet is an asset. In reality, it is cash converted into boxes on a shelf that may or may not sell. A business with $100K in inventory and $10K in the bank is more fragile than the balance sheet suggests.
What founders should remember
Your reorder point is your most important number
Calculate it with real lead times and safety stock. Automate the check. The cost of a stockout is lost revenue plus lost customer trust — both are hard to recover.
Start with conservative safety stock, then optimize with data
For a new product, 6–8 weeks of safety stock is not excessive. As you collect sales and lead time data, tighten to 3–4 weeks. Never go below 2 weeks of safety stock on a single-source product.
Inventory is a cash flow decision, not just an operations decision
Every unit on the shelf represents cash you cannot deploy elsewhere. Evaluate inventory levels alongside your marketing budget, new product investment, and runway.