Sellable stock, not on-hand
A warehouse count of 300 units does not mean 300 units can be sold. If 40 are committed to open orders, only 260 are available. If the team also wants to keep a 50-unit safety buffer, the number of units that can be sold before the buffer is touched is 210.
The calculator separates these layers: on hand, committed, safety stock and sellable. That prevents the most common coverage mistake — dividing total stock by daily sales and concluding there is more runway than the store can actually use.
The formula and a worked example
Sellable units = on hand − committed. Days of supply = sellable ÷ average daily sales. Days to safety stock = (sellable − safety stock) ÷ daily sales. Reorder gap = daily sales × lead time + safety stock − sellable, with a floor of zero.
On hand 300, committed 40, safety 50, daily sales 25 and lead time 14 days: sellable is 260, days of supply is 10.4, days to safety is 8.4, and the reorder gap is 25 × 14 + 50 − 260 = 140 units. Because 10.4 days is shorter than the 14-day lead time, the status is “coverage shorter than lead time.”
Three dates that matter
The stockout date is today plus days of supply. The safety-stock date is today plus days to safety. The reorder-now date is the date by which the purchase order must be placed to arrive before the stockout, which is the stockout date minus lead time.
Dates are more useful than days in a team calendar: they turn a ratio into a deadline. Recalculate after a sales spike, a large wholesale order or a supplier delay; the dates move immediately.
Coverage shorter than lead time
If days of supply is less than lead time, the current stock will not cover the next replenishment. The reorder gap shows how many units are missing to cover lead time plus safety stock. In the example, 140 units are needed just to reach the lead-time-plus-safety position.
A gap does not always mean an emergency. There may be inbound stock, a faster backup supplier or a planned allocation. The model does not know those; it flags the gap so the team can check them.
Where the model stops
Average daily sales are a planning rate. Seasonality, promotions, new product launches and wholesale orders can change the real rate quickly. Inbound purchase orders, multi-location allocation, backorders and bundle component demand are also outside the single-SKU view.
Use the safety stock calculator to derive a buffer from demand and lead-time variability, and the CSV reorder planner to apply review cycles, MOQ and pack multiples across many SKUs.
How to use it week to week
Run the calculation for the SKUs that carry the most revenue or the longest lead times, not every SKU every day. Compare the coverage date with the supplier’s next order window and set an alert a few days before the safety-stock date.
When the status changes, record why: a promotion, a late shipment or a data error. Those notes make the next reorder decision faster than the number alone.