Amazon FBA reorder point and safety stock calculator (US)
Run out at the fulfillment center and your sales stop until the next shipment is checked in. Send too much and it sits paying storage fees. Enter one product's daily sales and supplier lead time to get its reorder point, safety stock and how many units to send. Nothing leaves your browser.
The maths is the same for every marketplace; the example here is an overseas supplier shipping by sea. Selling on Amazon.in? India version.
Reorder in about 7.7 days, when stock falls to 1085 units.
Your numbers
- Reorder point
- 1085 units
- Safety stock
- 185 units
- Lead-time demand
- 900 units
- Days of cover now
- 80 days
- Order quantity
- 785 units
- Reorder in
- 7.7 days
Reorder in about 7.7 days, when stock falls to 1085 units.
“Email me my result” opens your own email app with the numbers filled in — we don't see or store them.
The formulas
- Reorder point = average daily units × lead time (days) + safety stock.
- Safety stock, statistical = z × √(L × σd² + d² × σL²), where d is average daily units, L the average lead time, σd and σL their standard deviations, and z comes from the service level (95% → 1.645).
- Safety stock, quick = (highest daily units × longest lead time) − (average daily units × average lead time).
- Order quantity = d × (L + cover days) + safety stock − (available + inbound).
Results are rounded up to whole units. They are estimates — seasonality such as Q4, promotions and your FBA capacity limits still need your judgement.
Reorder questions Amazon US sellers ask
What is a reorder point for an FBA product?
The stock level at which you place the next purchase order, so the new units are sellable at the fulfillment center before you run out. It is the demand you expect during the lead time (average daily units × lead-time days) plus safety stock.
What lead time should I use if my supplier is overseas?
The whole time from placing the order to units being available to sell: production, freight by sea or air, customs clearance, delivery to the fulfillment center and its inbound check-in. Use your own history. With overseas suppliers the lead time, and how much it varies, is often the biggest input, which is why the example uses a long one.
How is this different from Amazon's restock recommendations?
Seller Central gives its own restock suggestions. This calculator is a transparent check you control: your own sales, your own lead time and the service level you choose, with the formula shown. Your FBA capacity limits can still cap how much you can send, so check them before you book the shipment.
Which service level should I pick?
Higher service levels mean fewer stock-outs but more units held, and stored units cost storage fees. Pick a higher level for the products where a stock-out hurts most. It is a trade-off, not a rule.
How is the order quantity worked out?
Order-up-to level = average daily units × (lead time + the days you want the order to cover) + safety stock. The order quantity is that level minus the units you already have available and inbound, never below zero.
Related free tools
- Where is my FBA stock, and what does it trigger? — which states want you to register for sales tax because Amazon stores your inventory there.
- Amazon US settlement profit calculator — what your settlement really leaves you after fees, refunds and ads.
- Reorder-point calculator for Amazon.in sellers
Free for the first 50 sellers
Track reorder points for every product — free during early access
I'm building WidenMargin to watch inventory, reorder points and days of cover across your products. Join the early-access list and we'll email you when it's ready for Amazon US sellers. Your calculator numbers are never sent to us.
We only use your email to contact you about WidenMargin early access. Never sold or shared. Ask us to delete it any time. Privacy