Free Tool
Inventory Reorder Calculator
Running out of stock loses sales; ordering too early ties cash up in a shelf. This calculator sets the reorder point from daily sales, lead time and safety stock.
Planning estimate, not financial advice. All figures on this page are estimates or scenarios for planning purposes only, built from the numbers you enter. They are not financial, tax or legal advice, and no earnings are promised. Read the full financial disclaimer.
What this tool does
Enter the units sold per day, the supplier’s lead time in days, the safety stock you want to hold, your current stock and the order quantity you usually buy. The calculator shows the reorder point — the stock level that triggers an order — the days of stock you have left, and whether an order is due now.
The reorder point is the demand during the lead time plus the safety stock: if you sell 10 a day and the supplier takes 7 days, you need 70 units to cover the wait, plus whatever buffer you hold for a late delivery or a busy week. Order when the stock hits that number, not when the shelf is empty.
Try it
Waiting. Enter your daily sales, lead time and stock, then press Calculate.
How it works
Demand during the lead time is daily sales multiplied by the supplier’s lead time in days. The reorder point is that demand plus the safety stock. Days of stock left are current stock divided by daily sales, and days to the reorder point are the stock above the reorder point divided by daily sales.
The order quantity is not set by this tool — it is entered by you, usually from the supplier’s minimum or the quantity that earns the best unit price. The cycle length is the order quantity divided by daily sales, which tells you how often the order repeats.
Assumptions and limitations
The reorder point assumes steady demand. Real demand is not steady.
- Daily sales are an average. A promotion, a season or a viral post can double daily sales overnight — re-run the numbers when demand moves.
- Lead time is the supplier’s stated time, not a promise. Safety stock exists for the late delivery; if deliveries are always late, fix the supplier rather than growing the buffer forever.
- The calculator does not model holding cost, expiry or the cash tied up in stock. A large order quantity lowers the order frequency and raises the cash locked in the shelf.
- Count stock honestly. Stock on the shelf and stock in a box are both stock; stock already promised to a buyer is not.
Worked example
Example (illustrative inputs, not a real shop). Ten units a day, 7-day lead time, 20 safety stock, 85 units on hand, 200 per order:
| Item | Figure |
|---|---|
| Demand during lead time (10 × 7) | 70 units |
| Reorder point (70 + 20) | 90 units |
| Current stock | 85 units |
| Order now? | Yes — stock is below the reorder point |
| Each 200-unit order covers | 20 days |
Frequently asked questions
What is safety stock for?
Late deliveries and busy weeks. The reorder point covers the demand during the stated lead time; safety stock covers the demand when the delivery is late or sales spike. Without it, one late delivery means an empty shelf.
How do I choose a safety stock figure?
From your own history: the extra units you needed on the worst recent week, or the demand during the longest recent delay. A guess is better than zero, and a figure from your own records is better than a guess.
Should I order when stock hits the reorder point, or earlier?
At the point — that is what it is for. Ordering earlier ties cash up in stock; ordering later risks running out during the lead time. The point is the balance between the two.
What if my supplier’s lead time varies?
Use the longest recent lead time, not the average. The reorder point must cover the wait you actually face, and a supplier who sometimes takes 14 days needs a point built on 14, not on 7.