Reorder point calculator
The stock level that should trigger your next purchase order, from three numbers you already know. Formula shown, safety stock included, worked out as you type.
Reorder point = (daily usage × lead time) + safety stock
Not sure about safety stock? Work it out
Fills the safety-stock field with (max usage × max lead) − (average usage × average lead).
Fill in the three numbers above.
The formula, on one line
Reorder point = (average daily usage × lead time in days) + safety stock. The first half is the stock you will get through while the replacement order travels; the safety stock absorbs the weeks that refuse to be average.
Worked example: kraft boxes
A packaging wholesaler shifts 40 boxes a day on average. The supplier takes 7 days from PO to delivery. Bad weeks hit 60 a day and slow deliveries take 10 days, so safety stock = (60 × 10) − (40 × 7) = 320 units. Reorder point = (40 × 7) + 320 = 600 boxes. When the shelf hits 600, the PO goes out - not when someone notices it looks low.
How to pick each number
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Average daily usage
Take the last 90 days of sales or issues for the product and divide by 90. Use real movement data, not gut feel - the gut remembers the busy weeks and forgets the quiet ones.
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Lead time, honestly
Days from raising the PO to stock being on the shelf and bookable - including your supplier’s processing, transit, and your own receiving. Not the courier’s marketing number.
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Safety stock
The buffer for bad weeks. If you don’t track it yet, use the helper in the calculator: worst realistic demand during the slowest realistic delivery, minus the average case.
Where the formula needs watching
Seasonal lines
A 90-day average smooths away a peak. For seasonal products, calculate usage from the same season last year, or shorten the window as the peak approaches.
Long-lead imports
With 6-12 week lead times a single reorder point is thin protection. Review the point monthly and watch open POs against it - the maths is the same, the stakes are bigger.
Stale numbers
A reorder point set once and never revisited quietly rots as demand shifts. Recalculate quarterly, or whenever a stocktake shows drift.
Keep the whole loop on paper?
The free UK PO template raises the order and the stocktake template checks the shelf - this calculator sits between them.
Reorder point questions, answered
What is a reorder point?
The stock level that triggers a new purchase order. When on-hand quantity falls to the reorder point, you raise the PO - so the replacement stock arrives just before you run out, not after.
What is the reorder point formula?
Reorder point = (average daily usage × supplier lead time in days) + safety stock. The first part covers what you will sell or use while the order is on its way; the safety stock absorbs the bad weeks.
How do I work out safety stock?
The quick method: (maximum daily usage × maximum lead time) minus (average daily usage × average lead time). It sizes the buffer to your worst realistic week combined with your slowest realistic delivery. The calculator has a helper that does this for you.
What if my supplier has a minimum order quantity?
The reorder point tells you WHEN to order; the MOQ constrains HOW MUCH. Keep the trigger where the formula puts it, and order the larger of your preferred quantity and the MOQ.
A calculator tells you the number once
It cannot watch the shelf for you. In Straptory every product carries its reorder point against live stock: the replenishment report flags what needs ordering, and the PO is raised from the same screen - no spreadsheet, no mental arithmetic at the shelf edge.