Setting a Supplier Buffer You Can Defend

A supplier quotes twenty-one days. Your last four orders arrived in nineteen, thirty-four, twenty-two and forty-one. Averaging those gives twenty-nine, which is not a lead time, it is a comfort blanket. The number you should plan with sits closer to the worst realistic case, because stockouts happen in the tail, not the middle.

Separate the quote from the record

Keep two columns: promised and landed. Promised comes from the contract. Landed is the date the goods entered your warehouse, measured by you. After three months you will see whether the gap is stable or drifting. A stable gap is a planning constant. A drifting gap is a supplier problem you should raise in writing before it reaches your customers.

Then size the buffer against consequences, not against feelings. If a stockout costs a two-day delay and an apology, a thin buffer is rational. If it costs a cancelled contract or a penalty clause, the buffer should cover the landed tail plus one full reorder cycle. Cheaper to hold the stock than to hold the conversation.

Air freight is a comparison, not a virtue

Compare holding cost against expedited freight rather than against nothing. Holding thirty extra units for six weeks usually costs less than one air shipment of the same goods, so the buffer wins on arithmetic. That flips when the item is bulky, perishable, or financed at a rate that makes carrying it expensive. Run both numbers before choosing a default.

Actionable habit: note the landed date for every receipt in one shared sheet, and review the worst three gaps each quarter. Adjust the buffer only when a new worst case appears, not when a single delivery runs late. Changing the number every month means you never learn whether it holds.

Bigger buffers hide other problems

A generous buffer absorbs late deliveries so smoothly that nobody investigates them. Quality faults, order-entry mistakes and missed cut-offs all become invisible behind the extra pallet. Keep one line on your sheet for the reason each gap happened. If the same reason repeats three times, the buffer is treating a symptom you could cure.