A hardware shop orders every Monday. The paint rollers look fine — 12 on the shelf, ten days of sales. The supplier needs two weeks. This min-max inventory calculator gives each item its Min and its Max, and turns today's stock into an order list.
| Item | Sales a day | Lead time (days) | Safety stock | On hand | On order |
|---|
| Item | Min | Max | Order today | Status |
|---|
The calculator runs in your browser. Nothing you type is sent anywhere. The rows to order today are yellow.
Min = sales a day × lead time + safety stock
Max = Min + sales a day × days between orders
Min is the reorder point. Max is the level one order brings you back to. Between the two, the stock goes down with sales, and nobody has to decide anything.
A hardware shop orders once a week. For years, the owner walked the aisles on Monday and ordered what looked empty.
This Monday she gives five items a Min and a Max instead. She orders every 7 days:
| Item | Sales a day | Lead time | Safety stock | On hand | On order | Min | Max | Order today |
|---|---|---|---|---|---|---|---|---|
| Wood screws 4×40 | 6 | 5 | 10 | 38 | 0 | 40 | 82 | 44 |
| Wall plugs 8 mm | 4 | 5 | 8 | 60 | 0 | 28 | 56 | 0 |
| Masking tape 25 mm | 2.4 | 10 | 6 | 30 | 20 | 30 | 47 | 0 |
| Paint roller 18 cm | 1.2 | 14 | 5 | 12 | 0 | 22 | 30 | 18 |
| Sandpaper P120 | 15 | 3 | 20 | 150 | 0 | 65 | 170 | 0 |
The walk through the aisles would have ordered the masking tape: the shelf is at its Min. But 20 rolls are on the road from last week's order. Min-max sees them and orders nothing.
The same walk would have skipped the paint rollers. Twelve on the shelf is ten days of sales, and the shelf looks full. But the supplier needs 14 days. The rollers are 10 below their Min, and the order is 18.
The wall plugs are the opposite case: 60 on hand, above their Max of 56. The last order was too big, and the next ones can wait.
The shelf shows the stock. Min-max also sees the lead time and the goods on the road. The order of this Monday is two lines: 44 wood screws and 18 paint rollers.
One item per row: sales a day in B, lead time in days in C, safety stock in D, on hand in E, on order in F. Put the days between orders in J1. Then:
=ROUNDUP(B2*C2+D2,0)=MAX(ROUND(B2*C2+D2+B2*$J$1,0),G2+1)=IF(E2<=G2,MAX(H2-E2-F2,0),0)Filter column I for values above 0, and you have the order of the day. To find the buffer in D, use the safety stock calculator; for one item in more detail, the reorder point calculator.
Each item gets two levels. When the stock falls to Min, you order. You order enough to bring the stock back to Max. The order size changes with the stock you have; the two levels stay the same until you recalculate them.
Min = sales a day × lead time + safety stock. It is the reorder point: the stock that lasts until the new delivery arrives, plus a buffer for busy days. The safety stock calculator gives the buffer from the ups and downs of your sales.
Max = Min + the sales of one order cycle. If you order every week, Max holds one more week. If your orders are expensive to place, use Min + the economic order quantity instead, and order less often.
Because it will arrive. An item can sit at Min while last week's order is still on the road. Without the open order in the sum, you order the same goods twice.
Round the order up to the pack size or the supplier's minimum. If that pushes the stock far above Max every time, raise Max, or order that item less often.
When the sales rate or the lead time changes — for a season item, before each season. Levels from last winter make a summer item run out, or fill the shelf with slow stock.
In Golden Inventory each item has a Minimum, a Target (the Max of min-max) and a Maximum for the overstock line. On the Dashboard, Create PO drafts one purchase order per preferred vendor for every item at or below its Minimum: Target − on hand − on order. Start on the free plan, no card.