How to know when to reorder stock from a vendor before you run out

A snack and beverage distributor running twelve vans out of one depot bought from nine vendors. Some delivered in two days. Some took two weeks. The purchasing manager kept it all in his head and a spreadsheet he updated when he remembered to.

For the fast-moving SKUs — the cola variants, the big biscuit brands — the pattern was always the same. Stock looked fine on Monday. By Thursday a few routes were calling in short. By Friday the purchasing manager was calling the vendor asking for a rush delivery, paying whatever premium came with it, and apologizing to three route reps who'd had to skip line items on their calls.

Meanwhile a corner of the warehouse held four pallets of a slow-moving juice SKU from a different vendor, ordered "to be safe," that hadn't moved in six weeks. Cash sat in that stock instead of in the bank.

Both problems had the same root cause: nobody had a number that said when to reorder. There was a feeling — "we're getting low on the cola" — but a feeling isn't a trigger, and by the time it turns into a decision, the lead time clock has already been running for days.

Why "when we're getting low" always arrives too late

The mistake isn't ordering too rarely. It's ordering by how the shelf looks instead of by how long it takes to refill it. A reorder decision made at the moment stock looks thin ignores the one number that actually matters: how many days will pass between placing the order and the vendor's truck showing up at the dock.

That number is different for every vendor, and it's rarely what the vendor quotes. A vendor might say "we deliver in three days," but if they only run a route to your area twice a week, the real gap between "we're low" and "stock is on the shelf" can be closer to ten. Add the day it takes someone to actually notice the shortage and place the order, and a distributor operating on gut feel is often reordering five to seven days later than they think they are.

The fix distributors reach for first — bigger safety stock across the board — just trades one cost for another. Overstock the fast movers by a wide enough margin to never run out, and you tie up cash in your best-selling category, the one that's supposed to be turning fastest.

What a reorder point actually needs

A working reorder trigger for a distributor needs three numbers, tracked per SKU, per vendor:

Average daily sales for that SKU. Not a gut estimate — the actual sell-through from route settlements and counter sales over a recent window, so a seasonal spike or a dead week doesn't distort it.

Vendor lead time, measured, not quoted. The real gap between placing a PO with that vendor and stock landing on the shelf, based on your last several orders with them — not their sales pitch.

A safety buffer sized to the vendor, not a flat rule. A vendor with reliable two-day delivery needs a thin buffer. A vendor whose trucks show up "sometime this week" needs a fatter one. Using the same buffer for both means the reliable vendor carries excess and the unreliable one still runs out.

Put together: reorder point = (average daily sales × lead time) + safety buffer. When stock for that SKU from that vendor crosses the line, it's time to order — not when the shelf looks thin, and not on a fixed weekly schedule that ignores what's actually selling.

Making it run without a spreadsheet

The reason most distributors don't run this today isn't that the math is hard — it's that doing it by hand, per SKU, per vendor, across a catalog of hundreds of items, doesn't survive a busy week. The spreadsheet gets built once during a slow month and abandoned by the next one.

What makes it stick is tying the reorder point to the same system that already records the sales and the deliveries — so the lead time is measured from real PO-to-receipt history instead of a vendor's promise, and the daily sales figure updates itself instead of going stale. iotoms' procurement module calculates a reorder point per SKU per vendor from that data automatically and flags what's crossed the line, so the purchasing manager is choosing which PO to send today instead of trying to remember which nine vendors need checking.

Practical takeaway

• Pull your actual PO-to-receipt lead time for each vendor from your last several orders — don't use their quoted number.
• Calculate a reorder point per SKU per vendor: (average daily sales × lead time) + a safety buffer sized to that vendor's reliability.
• Give fast movers from slow vendors a fatter buffer; give fast movers from reliable vendors a thinner one — don't use one buffer for everything.
• Review and recalculate monthly, not once — sales velocity and vendor reliability both drift.
• Flag SKUs that cross their reorder point automatically instead of relying on someone noticing the shelf looks thin.