Projected Stockout Date and Days of Supply Calculator
When a supplier slips a delivery, the first question is how long you can last. This calculator turns on hand, demand and receipt timing into a stockout date and a shortage quantity.
Your numbers
Your results
Assumes constant daily demand. Use the actual demand profile from your MRP time buckets when demand is lumpy.
Shortage quantity vs receipt arrival day
Sweeps Days until that receipt from 0 to 80, holding your other inputs fixed.
Live shortage view over your ERP
Optional: ask how a read-only stockout projection could run on your own item and supply data.
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How to use it
Enter usable on hand, which should exclude quarantine, held and reserved stock, then average daily demand and the next scheduled receipt. The results show days of supply, when safety stock is breached, and how many days of demand go unserved if the receipt arrives after you run out. Move the receipt day to test a pushed out delivery.
- Use net available stock, not the gross book balance.
- Take demand from the next few weeks, not the annual average.
- Include only receipts with confirmed dates.
The method
Days of supply equals usable stock divided by average daily demand. The safety stock breach day uses stock above the safety level. If the receipt is due after days of supply, the gap is receipt days minus days of supply, and the shortage equals the gap times daily demand. If the receipt arrives in time, cover after receipt is the remaining stock plus the receipt, divided by demand.
Reading the result
With 1,800 units and 60 a day you have 30 days of supply and breach safety stock after about 23 days. A receipt due on day 40 leaves a 10 day gap and a shortage of 600 units. The chart shows the shortage growing linearly once the receipt passes day 30, which gives you a number to take to the supplier or to sales when deciding whether to expedite, substitute or reallocate.
Common mistakes
Planners often use demand averaged over a year when the next month is far heavier. Others include stock in quality hold, or count a receipt that is still only a planned order. Also check allocations: stock reserved to a single order may not be available to the line that is about to run out.
Frequently Asked Questions
What is days of supply?
It is usable inventory divided by average daily demand. It tells you how long current stock lasts if nothing else arrives and demand stays at the assumed rate.
How is it different from inventory turns?
Turns are an annual, aggregate measure of inventory efficiency. Days of supply is a forward looking, item level measure used to prioritize shortages and expedites.
Should safety stock count as available?
For planning it is protected stock, so a breach is a warning. For a true stockout date, it is available until it reaches zero. This tool shows both dates.
What if demand is not constant?
Use the sum of actual gross requirements over the horizon to find when cumulative demand exceeds supply. The result will differ from this average based estimate.
Netray can keep this calculation live over your ERP data and alert planners when projected stockout dates fall inside lead time.
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