Minimum stock is not what you have left, it is what you use while waiting

Running out of stock in a dental practice carries a cost that appears nowhere: the appointment postponed, the patient called back, and the emergency purchase at the first price available.

The commonest way of avoiding it is to keep plenty of everything, which solves one problem by creating another: capital sitting in a cupboard and products expiring before use.

The correct method requires a simple calculation almost nobody performs, because it looks more complicated than it is.

Minimum stock is the quantity you consume during the time a reorder takes to arrive. If you use ten units a week and delivery takes a week, your minimum stock is ten units.

Below that threshold you are already late, even if there is still stock visible in the cupboard. That is the point most often got wrong: people look at what is left rather than at what is consumed while waiting.

To this is added a safety margin absorbing variation: a week with more procedures than expected, or a delivery slower than usual.

The margin should not be uniform. It needs to be generous on critical items, meaning those without which an appointment stops, and can be minimal on substitutable or non-urgent ones.

Distinguishing the two categories is the step yielding the greatest result. Most items in a practice are not critical, and treating them all alike wastes space and money.

Items with an expiry date call for the reverse reasoning: stock is kept low even when they are critical, because the cost of an expired product is certain while running out is only possible.

Calculating consumption requires knowing it, and here the order history proves useful. The dates of past reorders reveal the rate at which an item runs down, with no register to keep.

Lead time should be verified against the actual supplier rather than estimated. A supplier delivering in three days permits far lower stock than one taking ten, and that changes the calculation for every item you buy from them.

It follows that choosing a supplier is not only about price. An item costing slightly more but arriving in half the time can allow stock to be halved, and the capital freed is worth more than the price difference.

In summary: minimum stock is consumption during lead time rather than what remains, the safety margin should be generous only on critical items, products with expiry dates want low stock, the order history gives the rate of consumption, and a fast supplier permits lower stock.