Amazon FBA Restock Calculator

Reorder point = (average daily sales × lead time in days) + safety stock units. If you sell 10 units/day, your lead time is 60 days, and your safety stock is 14 days, your reorder point is 10×60 + 10×14 = 740 units. When FBA stock drops to that number, place the next order. This calculator does that math from your inputs and also tells you exactly how many days from today that will be.

Days of supply = current FBA stock ÷ average daily sales. It's how long your inventory lasts at the current pace. Amazon shows it as "Historical days of supply" in Seller Central. Below 28 days, Amazon charges a per-unit low-inventory-level fee — so 28 days is a critical floor for FBA sellers.

Introduced by Amazon in 2024, the low-inventory-level fee is a per-unit surcharge applied whenever your historical days of supply falls below 28 days. The fee varies by size tier (around $0.13–$0.89/unit). Avoid it by treating 28 days as a hard floor: this calculator warns whenever you cross under it, and you can plan around it by expediting shipping or sizing your safety stock to keep DoS above 28.

The simplest approach is to express safety stock as days of buffer above lead-time demand — typically 14 to 30 days. Multiply that by your average daily sales to get units. For more volatile categories, size safety stock based on the standard deviation of daily sales (or the highest realistic spike), not the average. Steady SKUs can run leaner; volatile ones need more.

A realistic lead time = manufacturing + transit + Amazon receive. China-to-USA by sea is often 60–90 days end-to-end; domestic suppliers can be 14–30 days. Always include Amazon's receive step (often 5–10 days from the moment the carrier delivers to FBA). Underestimating this is the most common cause of FBA stockouts.

Days of supply tells you when your stock will hit zero; days until reorder tells you when you should ORDER. If you only watch days of supply and order on the empty date, you'll stock out for a full lead time. Days until reorder bakes in lead time and safety stock — it's the actionable number.

A typical starting point is 14 days for steady SKUs and 30 days for volatile ones. Push higher if your supplier is unreliable, your transit goes by sea, your category is seasonal, or you're running heavy PPC that can spike velocity. Push lower only if you have a fast, reliable supplier and tight cash flow.

Yes. The "Units In Transit" field subtracts 1-for-1 from the recommended order quantity. If you already have 200 units on the boat, the next order is sized 200 units smaller. This stops you from double-ordering when a previous shipment hasn't arrived yet.

Order Qty = daily sales × (lead time + safety stock + target cover) − current stock − units in transit. The idea: by the time the new order arrives, your total inventory (this order + whatever's left of the old) should equal (safety + target cover) days of supply. That's a smarter sizing than the common "1.5× lead-time demand" heuristic used by most free calculators.

IPI (Inventory Performance Index) is Amazon's 0–1000 score measuring how well you manage FBA inventory. It combines sell-through rate, stranded inventory, excess inventory, and in-stock rate. A low IPI shrinks your restock limits — the maximum units of a storage type you can send to FBA. If your IPI is low, restock smaller and more often, and clear stranded/excess inventory before sending more.

Yes — and you should. As soon as your launch has 7–14 days of real velocity, run the calculator to get the first reorder point. Lead time matters more during launches because you're sizing initial orders against uncertain demand. Re-run weekly during the launch ramp so reorders don't lag the velocity trend.

The FBA Profit Calculator works at the per-unit level — what each sale earns after fees. This Restock Calculator works at the per-time level — when to reorder and how much. They're complementary: profit-per-unit (from the profit calc) × units-per-cycle (from this one) = profit per restock cycle, which this calculator surfaces directly.

Recalculate monthly at minimum, and any time your velocity shifts (a new ad campaign, a viral moment, seasonal change, supplier delay). Velocity drifts — a reorder point sized 90 days ago might be wrong today. The calculator is fast enough that there's no excuse not to refresh.

For seasonal SKUs, bump up "Average Daily Sales" to reflect expected Q4 velocity (often 2× or 3× baseline) and re-run the calculator in August or September. That gives you the Q4 reorder point and order quantity in time to place the order — Q4 lead times often stretch as suppliers and carriers fill up, so plan early.

Order Now means you're past the reorder point but you still have more than your lead time of inventory left — order today and the new shipment will arrive before stockout. Critical means your days of supply is already less than your lead time — even ordering today, you'll stock out before the new shipment arrives. In the Critical band, expedite shipping or accept the stockout window.

No. Every calculation runs entirely in your browser — nothing is sent to a server or stored. You can share a link that reopens the calculator with the same inputs, but the numbers travel in the URL, not through us.