Supplier lead time is the number of days between placing a purchase order and the stock landing on your shelf. Multiply your average daily demand by that lead time, add safety stock for variability, and the result is your reorder point: the on-hand quantity that triggers a new order before you run out.
A shortage rarely starts on the floor. It starts weeks earlier, when nobody wrote down how long a vendor actually takes to deliver, or when the number on file was true two years ago and nobody updated it. A buyer eyeballs the shelf, guesses it is "probably fine for another month," and places the order a week too late. The part sits on backorder, the work order waits, and the customer gets a new ship date instead of their order.
The flip matters here: most software shows you the problem and leaves you the work. A low-stock alert, a red number on a dashboard, a report nobody opens until Friday. That is information, not action. The gap is not data. It's the distance between knowing a number is low and getting a purchase order sent before it costs you a sale.
What actually counts as supplier lead time
Lead time is not just "how long the box takes to ship." It is the full stretch from the moment you send the purchase order to the moment the item is received, counted, and available to sell or build with. That includes:
- Order processing time on the supplier's side, before they even start picking or manufacturing your order.
- Production or pick-and-pack time if the item is made or kitted to order.
- Transit time from the supplier's dock to yours, including customs if the item crosses a border.
- Your own receiving and put-away time, which still adds a day or two even in a tight operation.
Track this per supplier and per item, not as one company-wide average. A domestic packaging vendor with a 3-day lead time and an overseas component supplier with a 60-day lead time cannot share a reorder formula. Blending them into one number is how a buyer ends up short on the slow item while sitting on too much of the fast one.
The reorder point formula, step by step
The math itself is simple. Getting clean inputs is the hard part. Here is the order of operations:
- Find average daily demand for the item, using recent sales or usage history, not a gut number from memory.
- Find the supplier's actual lead time in days, based on the last several purchase orders, not the number quoted when you first opened the account.
- Multiply average daily demand by lead time. This is your lead time demand: what you expect to sell or use while waiting on the next shipment.
- Add safety stock, calculated from how much that lead time or demand actually varies order to order.
- The total is your reorder point. When on-hand quantity drops to that number, it is time to place the next order, not after.
A simple version of the safety stock piece: take the difference between your longest recent lead time and your average lead time, then multiply by average daily demand. A supplier that is always within a day of quoted lead time needs a thin cushion. A supplier that swings between 10 and 25 days needs a much thicker one, even if the average looks fine on paper.
Why safety stock is not optional
Safety stock is not padding for buyers who like to feel comfortable. It is the number that absorbs the two things that break a reorder point: a supplier running late, and demand running hotter than expected in the same window. Skip it and your reorder point only works on a perfect week, and perfect weeks are rare on a shop floor.
The tradeoff is real. Too little safety stock and you are the manufacturer calling a customer to push a ship date. Too much and cash sits in a bin instead of in the business, tying up warehouse space you could use for something that actually moves. The right number sits between those two costs, and it looks different for a cheap fast-mover than for an expensive long-lead component.
Picking a reorder strategy that fits the item
Not every SKU needs the same approach. These are the common strategies worth matching to how an item actually behaves:
- Fixed reorder point. One static trigger quantity per item. Works for stable, low-variability items where demand barely moves month to month.
- Lead time demand reorder point. The calculation above, rebuilt whenever lead time or demand shifts. Fits items where either number moves often.
- Seasonal reorder points. Separate thresholds for peak and off-peak months, so you are not carrying peak-season safety stock in the slow months or running short right before the rush.
- Just-in-time ordering. Tight reorder windows for items with short, dependable lead times, where carrying extra stock costs more than the small risk of a late order.
- ABC analysis. Rank items by sales volume or dollar impact, then give the small number of A items that drive many of your sales dollars closer reorder-point attention, with lighter rules for the C items that make up the rest of the catalog.
A furniture maker buying imported hardware on a 60-day boat might run seasonal reorder points stacked on top of lead time demand. A distributor reselling a fast domestic item might run just-in-time with almost no safety stock. The strategy follows the item, not a company-wide default.
Where this breaks down without the right system
Here is where a spreadsheet or a basic accounting tool runs out of road. QuickBooks and Xero were built to keep the books, not to track a moving lead time per supplier, hold a safety stock formula per item, and flag items that cross a reorder point across every SKU you carry. Fishbowl runs inventory, production, and the warehouse. QuickBooks or Xero keeps the books.
Fishbowl is the platform. Fishbowl Inventory, Fishbowl Advanced Manufacturing, and Fishbowl Advanced Warehouse are purpose-built parts of Fishbowl, matched to how the business runs. On Fishbowl Inventory, the AI Operations Specialist uses live Fishbowl data to prepare purchase orders, sales orders, transfers, receipts, and adjustments for your approval. Nothing is saved or changed without the operator's approval. Ask, Approve, Done.
When an item's on-hand quantity drops to its reorder point as recorded in Fishbowl, the AI Operations Specialist can prepare a purchase order built from the actual supplier, the actual lead time, and the quantity the formula calls for, so you are reviewing a drafted PO instead of waiting for someone to notice the shelf is thin. It works from the transactions your team has already entered in Fishbowl, updated as those entries happen, not from a feed pulled continuously off every system you own. Brian Garrett at Telluric Companies, a beta tester, says the AI Operations Specialist saves him at least 45 minutes per purchase order. See Fishbowl's case studies for more on how that PO workflow plays out across different operations.
Setup and training typically run 6 to 8 weeks with Fishbowl's own team, and the system is useful from your first live count, not just after the full rollout finishes. Customers can reach a person by phone, email, or chat when a question comes up, in-house in the US or APAC depending on where you operate.
- Do you know your actual lead time per supplier, based on recent orders, not the number you were quoted at signup?
- Do your reorder points account for how much that lead time varies, not just its average?
- Can your current system prepare the purchase order when the threshold is crossed, or does a person have to notice first?
- Have you recalculated reorder points in the last three months, or are they left over from last year?
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Fishbowl does the work. You make the call.
Frequently asked questions
What is the difference between lead time demand and safety stock?
Lead time demand is how much you expect to sell while waiting for a purchase order to arrive. Safety stock is the extra cushion you hold on top of that number to cover late shipments, demand spikes, or a supplier that misses a date. Reorder point combines both.
How often should I recalculate my reorder points?
Check reorder points at least quarterly, and sooner any time a supplier's lead time shifts, demand for an item changes season to season, or you add a new vendor. A reorder point set once at launch and never touched again is usually wrong within a year.
Does a longer supplier lead time always mean I need more safety stock?
Usually, but not automatically. A long lead time that is also reliable and consistent needs less safety stock than a shorter lead time from a supplier that misses dates often. Variability in the lead time matters as much as its length.
How long does it take to get reorder points working in Fishbowl?
Paid setup and training typically run 6 to 8 weeks with Fishbowl's own team, but the product is useful from your first live count. Reorder points, lead times, and safety stock can be entered item by item as your data gets cleaned up.