Inventory Reorder Point Calculator
The reorder point (ROP) is the inventory level at which you should place your next purchase order so new stock arrives before you run out. Get it right and you avoid the two most expensive inventory mistakes: stockouts (lost sales, lost rank on Amazon and Etsy, angry customers) and over-ordering (tied-up cash and storage fees). This calculator gives you your reorder point, days until stockout, recommended order quantity, and a health badge so you know at a glance whether to place a PO today.
Last Updated: June 2026
New calculator — reorder point, safety stock, and stockout risk for ecommerce inventory.
- Free calculator
- Instant estimate
- No signup needed
- Beginner friendly
Mean units sold per day over the last 30–90 days.
Order placed → stock available to sell.
On-hand sellable units across all warehouses.
Buffer for demand spikes or supplier delays.
Leave blank if you can order any quantity.
Reorder point
208
(Daily × Lead) + Safety
Days until stockout
15 d
At current daily sales
Current inventory status
180
28 units below ROP
Recommended reorder qty
68
Units to order now
Safety stock level
40
3.3 days of cover
Daily usage
12 units/day
Average over your tracking window
At 12 units sold per day with a 14-day lead time, your reorder point is 208 units. You currently have 180 units, which is about 15 days of cover. Reorder roughly 68 units now to stay ahead of demand and rebuild your safety stock.
You're within 20% of the reorder point. Place a purchase order soon to avoid cutting it close.
All calculations are estimates based on average platform fees. Real profits may vary depending on category, ads, and shipping.
Free worksheet for your next step
Turn this calculator result into a plan with a matching worksheet, checklist, or printable resource.
- PlannerAmazon FBA
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How to use this calculator
- Enter your numbers in each field above — the calculator updates instantly as you type, so there's nothing to submit.
- Use your real figures when you have them, or sensible estimates while you're planning. If a field doesn't apply, leave it at zero.
- Compare the results, then change one input at a time to see how each lever (price, cost, fees, volume) moves the outcome.
Formula
Reorder point = (Average daily sales × Lead time in days) + Safety stock · Days until stockout = Current inventory ÷ Average daily sales · Recommended reorder quantity = (Max(Current inventory, Reorder point) + Safety stock) − Current inventory · If the result is negative, no order is needed (display 0). If a supplier MOQ is set and the recommended quantity is below it, round up to the MOQ.
Worked example
You sell 12 units per day, your supplier lead time is 14 days, you have 180 units on hand, and you keep 40 units of safety stock.
- Reorder point = (12 × 14) + 40 = 168 + 40 = 208 units
- Days until stockout = 180 ÷ 12 = 15 days
- Current inventory (180) is below ROP (208) → reorder needed
- Recommended quantity = (max(180, 208) + 40) − 180 = (208 + 40) − 180 = 68 units
- Health = Red (below reorder point). Place a PO today.
Answer: ROP 208 · 15 days of cover · order 68 units now
How it works
Why reorder point matters: lead time is unforgiving. If you wait until stock is low to place an order, the new shipment can't teleport — it still takes the full lead time to arrive. ROP works backwards from that reality: it's the level where you have just enough stock to last through the lead time, plus a buffer for surprises.
How to calculate safety stock: a simple starting point is 1–2 weeks of average daily sales — that's enough to cover a modest delay or sales spike. More sophisticated stores use the formula safety stock = Z × σ × √lead time, where Z is a service-level multiplier (1.65 for 95%, 2.33 for 99%) and σ is the standard deviation of daily demand. The higher your service level target, the more safety stock you need.
Lead time variability is the silent killer: stockouts almost always happen because a supplier was slow, not because demand was wild. Track actual lead time on every PO — if your supplier sometimes ships in 14 days and sometimes in 21, size safety stock for the slower case, not the average.
Amazon FBA specifics: add inbound shipping and FBA receiving time (often 5–10 days) to your lead time. A 14-day supplier lead time is really a 21–24 day total lead time before units are FBA-active.
MOQ considerations: if your supplier requires a minimum order quantity higher than your recommended reorder, you'll order more than the math suggests — but you'll also push out your next reorder date. Don't let MOQ pressure you into over-ordering slow-moving SKUs.
How to interpret your results
- Dollar values are shown per sale, per order, or per item unless a result is explicitly labelled monthly, weekly, or daily.
- Percentages (margin, ROI, conversion rate) are easier to compare across products and price points than raw dollars — use them when you benchmark.
- A positive result means you're ahead after the costs and fees you entered. A negative result means the current numbers don't work — change a lever (raise price, cut a cost, lower ad spend) and recalculate.
- Treat the output as a planning estimate, not a guarantee. Fees, taxes, and conversion rates shift over time — re-run the numbers whenever a key input changes.
Common mistakes
- Forgetting inbound and receiving time when selling on Amazon FBA — your real lead time is supplier lead time + transit + FBA receive.
- Sizing safety stock from average daily sales only and ignoring sales spikes (holidays, viral posts, ad scaling).
- Treating lead time as a single number when your supplier's actual delivery varies by 30–50%.
- Skipping a reorder because cash flow is tight — a stockout almost always costs more than the inventory would have.
- Using ROP for every SKU equally. Fast movers need bigger buffers; slow movers tie up cash if you over-buy.
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FAQ
- What is a reorder point?
- The reorder point is the inventory level at which you should place a new purchase order so the next shipment arrives before you run out. It equals average daily sales × lead time, plus a safety stock buffer.
- How do I calculate safety stock?
- A practical starting point is 1–2 weeks of average daily sales. For a more precise figure, use Z × σ × √lead time, where Z is a service-level multiplier (1.65 for 95%, 2.33 for 99%) and σ is the standard deviation of daily demand.
- What is a good lead time for ecommerce inventory?
- It depends on your supplier and channel. Domestic suppliers typically run 7–14 days; overseas (often China) is usually 30–60 days door-to-door. Amazon FBA adds another 5–10 days of receiving time on top of supplier lead time.
- How is reorder point different from reorder quantity?
- Reorder point is WHEN to order — the stock level that triggers a new PO. Reorder quantity is HOW MUCH to order — typically enough to refill to your target level, respecting supplier MOQ and your cash flow.
- Does this work for Amazon FBA?
- Yes — just remember to use total lead time (supplier production + transit + FBA receiving), not just supplier lead time. FBA receive can add 5–10 days, and stockouts on Amazon damage your sales rank, so most FBA sellers run a larger safety stock than DTC sellers do.
Why trust this calculator?
This tool uses standard mathematical formulas and commonly accepted calculation methods, shown openly in the Formula section above so you can verify the math yourself. Results are estimates based on the information you enter and do not account for every individual circumstance. For important financial, tax, legal, medical, or business decisions, please double-check with a qualified professional before acting on the numbers.
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One calculator rarely tells the full story. Pair this one with a related tool below to pressure-test your numbers from a different angle, or browse Work & Money Calculators for more in the same category.
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