Free FBA tool
FBA Restock Calculator
Find your Amazon FBA reorder point, the safety stock to hold, and exactly how many units to order, from your own sales velocity and real lead times. Everything updates live as you type. No login, no ASIN, nothing stored.
Your numbers
Lead time (the FBA three-part chain)
Safety stock method
Reorder point
3,960 units
At 40 units/day you reach this level in about 26 days. That is when the PO goes out.
Suggested order qty
0 units
To reach your order-up-to target
Safety stock
800 units
20-day buffer
Total lead time
79 days
Production + freight + receiving
Days of cover
125 days
At current velocity
How the reorder point breaks down
- Lead time demand(40 units/day x 79 days)3,160 units
- Safety stock(20 day buffer)800 units
- Reorder point(Reorder when sellable stock falls to this level)3,960 units
The formula behind the calculator
Reorder point
Reorder point = (average daily sales x total lead time) + safety stock
Total lead time = supplier production days + freight transit days + Amazon receive and check-in days
Suggested order quantity
Order qty = order-up-to level − units on hand − units inbound
Order-up-to level = average daily sales x (lead time + review period) + safety stock
Safety stock (simple)
Average daily sales x buffer days. A fast cushion when you do not track demand variability yet.
Safety stock (statistical)
z(service level) x daily demand standard deviation x square root of lead time. Sizes the buffer to how spiky your sales actually are.
Worked example
A SKU sells 40 units a day on a steady trend. The supplier needs 30 days to produce. Ocean freight plus drayage runs 35 days door to Amazon. Amazon then takes another 14 days on average to receive, scan, and make the shipment sellable. Total lead time is 79 days, not the 30 the supplier quoted.
- Lead-time demand: 40 units x 79 days = 3,160 units
- Safety stock (20-day buffer): 40 x 20 = 800 units
- Reorder point: 3,160 + 800 = 3,960 units
The moment sellable inventory hits 3,960 units, the PO goes out. A seller who used the 30-day supplier number alone would set a reorder point near 1,200 units and run out roughly seven weeks before the next shipment cleared. That is the load-bearing reason to use real lead times. For the math in prose, see the reorder point guide; for sizing the buffer, the safety stock guide.
Key terms
- Reorder point
- The on-hand inventory level that should trigger a new purchase order. Below it, you risk stocking out before the next shipment is sellable.
- Safety stock
- The buffer you hold on top of expected lead-time demand to absorb sales spikes and lead-time slippage without going to zero.
- Days of cover
- How long your current on-hand stock lasts at your average sales rate. Falling days of cover is the early warning that a reorder is due. In 2026, Amazon also charges a low-inventory-level fee when your historical days of supply sit below about 28 days, so keep your reorder point and safety stock above that floor. More in the reorder point guide.
Frequently asked questions
How do you calculate an FBA restock quantity?
Start from your reorder point: average daily sales times total lead time, plus safety stock. When sellable stock hits that level, order enough to reach your order-up-to target, which covers the next lead time plus your review cycle plus safety stock, minus what you already have on hand and inbound. This calculator does all of that live as you type.
What is the reorder point formula for Amazon FBA?
Reorder point equals (average daily units sold times total lead time in days) plus safety stock. For FBA, total lead time is supplier production plus freight transit plus Amazon receiving and check-in, which in 2026 commonly runs far longer than the supplier quote alone.
Should Amazon receiving time count toward lead time?
Yes. Units sitting in transit or in Amazon's receive queue are not sellable and do not protect your rank. Measure your real check-in time from recent shipments and add it to every restock calculation. It is routinely one to three weeks and the most underestimated input.
How much safety stock should I hold?
Two ways. The simple method holds a fixed buffer of days of demand. The statistical method sizes the buffer from your demand variability and a target service level, using z times daily demand standard deviation times the square root of lead time. Steadier sales need less buffer; spiky demand needs more. This version models demand variability only, not lead-time variability, so if your Amazon receiving time swings a lot, widen the buffer to compensate.
Is this restock calculator free and can I embed it?
Yes. The calculator is free, runs entirely on the numbers you type, and stores nothing. You can embed it on your own site or blog with the iframe snippet near the bottom of the page.
Embed this calculator
Free to use on your own site or blog. Paste this snippet where you want the calculator to appear.
<iframe src="https://www.inventoryhero.ai/embed/fba-restock-calculator" title="FBA Restock Calculator by Inventory Hero" width="100%" height="720" style="border:1px solid #e5e5e5;border-radius:16px;max-width:680px" loading="lazy"></iframe>Stop recalculating restocks by hand
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