01
Enter demand & stock
Your average daily sales and current FBA stock. These set your days of supply and the urgency of restocking.
Amazon FBA Restock Calculator
Reorder point, days to reorder, and order quantity — no spreadsheets needed.
Updated Reviewed by Sajid Hussain· Editor
What is FBA restocking?
When to reorder, how much to order — without the spreadsheets
Amazon FBA restocking is the process of replenishing inventory before it runs out — calculating the exact reorder point, order quantity, and timing that keeps a listing in stock without over-investing in warehouse space. The reorder point equals lead-time demand plus safety stock: a SKU selling 10 units per day with a 60-day lead time and 14-day safety buffer hits its reorder point at 740 units. Order any later and the new shipment arrives after a stockout; order much earlier and long-term storage fees erode the margin the restock was meant to protect. This calculator computes all four planning numbers — reorder point, days until reorder, recommended order quantity, and days of supply — and surfaces Amazon's 28-day low-inventory-level fee threshold, in any currency, without logging in.
The four numbers every FBA restock decision needs. Daily sales, current FBA stock, lead time, and safety stock feed into: your reorder point (the inventory level at which to order), days until reorder (the actionable date), recommended order quantity (sized to cover the next cycle), and days of supply (your runway).
The cost of getting restocking wrong is huge. Stock out and you lose ranking, Buy Box, and ad ROAS. Over-order and you pay long-term storage fees while capital sits in a warehouse. Since 2024, Amazon also charges a per-unit low-inventory-level fee whenever your historical days of supply drops below 28 — which most free calculators ignore but ours surfaces clearly.
We close the planning loop. Where most free calculators show a reorder point and stop, this one gives you the date to place the order — not just the stockout date. It accounts for units in transit, sizes the order to cover your full (lead + safety + cover) window, and flags the 28-day fee threshold and excess-stock risk.
Use it across the full Amazon planning cycle. Before every restock, during a launch, in Q4 prep, or whenever a campaign changes your velocity. Pairs with our Amazon FBA Profit Calculator (per-unit economics) and Amazon PPC Break-Even Calculator — together they cover the seller's full planning loop, free.
Quick facts
- Heroes computed
- Reorder Point · Days Until Reorder · Order Qty · DoS
- Closes the loop
- Days-until-REORDER, not just stockout
- Amazon-aware
- 28-day low-inventory-fee warning
- In-transit handling
- Reduces next order 1-for-1
- Marketplaces
- 9 regions · auto currency
- Time to answer
- < 5 seconds
How it works
From four product numbers to the exact order to place
Two inputs about demand and stock, two about lead time and safety — and you have your reorder point, your timing, and the size of the next order.
02
Add lead time & safety
Total lead time from order to FBA receipt, plus the safety-stock buffer above it. Together these set your reorder point.
03
Read the verdict
Get reorder point in units, days until you should reorder (not just stockout), and the inventory status — Healthy, Order Soon, Order Now, or Critical.
04
Order the right quantity
The recommended order quantity is sized to cover your target window after the shipment lands — netting out whatever's already on hand and in transit.
Steps to use the Amazon FBA Restock Calculator: Enter demand & stock, Add lead time & safety, Read the verdict, Order the right quantity.
The math
Formula breakdown
No black boxes. Here is the exact math behind every output. The whole tool turns on one foundation: lead-time demand + safety stock = the inventory level at which you should reorder.
01
Lead-time demand
Lead-time Demand = Average Daily Sales × Lead Time (days)
The units you will sell during the time a new order is in transit. Half of the reorder-point formula.
02
Safety stock (units)
Safety Stock Units = Average Daily Sales × Safety Stock Days
The buffer above lead-time demand, expressed as units. Protects against demand spikes and supplier delays.
03
Reorder point
Reorder Point = Lead-time Demand + Safety Stock Units
The inventory level at which to place the next order. Order any later and you risk stocking out before the new shipment arrives.
04
Days of supply
Days of Supply = Current Stock ÷ Average Daily Sales
How long your current FBA inventory lasts at the current pace. Below 28 days, Amazon charges the low-inventory-level fee per unit.
05
Days until reorder
Days Until Reorder = (Current Stock − Reorder Point) ÷ Average Daily Sales
The actionable date — when you should place the order. Negative means you're already past the reorder point; positive is days from today.
06
Recommended order quantity
Order Qty = Daily Sales × (Lead Time + Safety + Target Cover) − Current Stock − Units In Transit
Sized so total inventory at the moment of arrival equals (safety + target cover) days of supply. Clamped to ≥ 0 — if you have more than enough, don't order.
07
Low-inventory-level fee threshold
If Days of Supply < 28 → Amazon adds the low-inventory-level fee per unit
Amazon's 2024 surcharge. The fee varies by size tier (roughly 0.13 to 0.89 per unit in the marketplace currency). Our warning fires whenever you cross under it.
Worked example
See it on a typical SKU
Let's walk a healthy SKU all the way from inputs to the order you should actually place.
Scenario
You sell 10 units/day, you have 900 units at FBA right now, your lead time is 60 days, you keep 14 days of safety stock, and you want each shipment to cover 60 days. Here's what those four numbers tell you about your next order.
1
Step 1 · Lead-time demand + safety stock
Across the 60 days a new order is in transit, you will sell 600 units — that's your lead-time demand. On top of that you keep 14 days of buffer: at 10 units/day, that's 140 units as a hard reserve.
Lead-time demand 600 units + safety stock 140 units
2
Step 2 · Reorder point
Add lead-time demand to safety stock: 600 units + 140 units = 740 units. When your FBA stock drops to 740 units, you order — not before, not after.
Reorder point: 740 units
3
Step 3 · Runway and timing
Days of supply = 900 units ÷ 10 units/day = 90 days. Days until the reorder point = (900 units − 740 units) ÷ 10 units/day = 16 days. Status: Healthy.
16 days until you should order
4
Step 4 · The size of the next order
You want enough so that when the order arrives, you're back to (safety + cover) days of stock. That's 10 units/day × (60 days + 14 days + 60 days) − 900 units = 440 units. (If you had units in transit, subtract those too.)
Order: 440 units
5
Step 5 · Cycle economics
Over the 60 days this order covers, you sell 600 units. At your profit per unit, that's about $6,000.00 in net profit per restock cycle — useful when deciding how aggressively to scale ads on this SKU.
Per cycle: 600 units sold
The takeaway
You're in a healthy zone — 16 days until the next reorder, an order of 440 units sized to cover the full lead-time + buffer + cover window, and your days of supply (90 days) sits well above Amazon's 28-day low-inventory-level fee threshold. Recheck whenever sales velocity shifts.
Reference benchmarks
What good looks like
Rough Amazon FBA reference ranges. Treat them as a sanity check, not a target — your right answer depends on your category, capital, and how volatile demand is.
| Metric | Poor | Average | Good | Excellent |
|---|---|---|---|---|
Days of supply Amazon FBA Low-Inventory-Level Fee Policy | < 28 (fee zone) | 28–60 | 60–120 | 60–90 stable |
Lead time (end-to-end) Jungle Scout State of the Amazon Seller Report 2025 | > 120 days | 60–120 | 30–60 | < 30 days |
Safety stock buffer Amazon FBA Restock Guide 2025 | 0 days | 7–14 | 14–30 | 14–21 + variability buffer |
Months of supply Amazon Inventory Performance Index Guidelines | > 6 (LTSF risk) | 2–4 | 1.5–3 | ~2 months |
Restock cycle SoStocked Amazon Inventory Management Guide 2025 | ad-hoc | 60 days | 45–60 days | rolling cadence |
Why this calculator
Calcrux vs Amazon Restock Tool vs paid suites vs spreadsheets
Amazon's own Restock Tool requires Seller Central. Paid suites give you depth but charge for it and lock to one marketplace. This is the same depth, free, in any currency — and surfaces things even Amazon's tool buries.
| Feature | Calcrux | Amazon Restock Tool | Helium 10 (Paid) | Spreadsheet |
|---|---|---|---|---|
| Reorder point from your data | Partial | Manual | ||
| Days of supply | Manual | |||
| Days until REORDER (not stockout) | Partial | Manual | ||
| Recommended order qty (smart) | Manual | |||
| Units-in-transit netting | Manual | |||
| 28-day low-inventory-fee warning | Partial | |||
| Excess-stock warning (LTSF risk) | Manual | |||
| Restock-cycle profit projection | Manual | |||
| Any marketplace & currency | Per-account | Manual | ||
| Smart insights | ||||
| Works without logging in | ||||
| Time to answer | 0 sec | Login | Login + $$ | 20+ min |
Common mistakes
What sellers get wrong about FBA restocking
The traps that turn a routine restock into a stockout — or a long-term storage problem.
Confusing days of supply with days until reorder
Why it matters
Days of supply tells you when you'll be empty; days until reorder tells you when you should ORDER. Order on the stockout date and you stock out for a full lead time.
Fix
Always act on "days until reorder" — it bakes in your lead time. Plan to order on that date, not your stockout date.
Treating lead time as just "manufacturing"
Why it matters
Real lead time = manufacturing + transit + Amazon receive. Skipping the FBA receive step (often 5–10 days) is the biggest cause of unexpected stockouts.
Fix
Use a total lead time that includes Amazon's receive window. Pad it slightly if your transit is by sea.
Picking safety stock by gut
Why it matters
Too low and any demand spike or supplier delay stocks you out. Too high and you bleed capital and risk long-term storage fees.
Fix
Start at 14 days, then size up based on demand variability and supplier reliability. Volatile categories or unreliable suppliers warrant 30+.
Ignoring the 28-day low-inventory-fee threshold
Why it matters
Since 2024, Amazon charges a per-unit fee when your historical days of supply falls below 28. The fee compounds your already-thin margins.
Fix
Treat 28 days of supply as a hard floor. If you ever cross it, restock immediately — the fee per unit usually exceeds the cost of expediting shipping.
Over-ordering once and getting stuck in long-term storage
Why it matters
Inventory aged over 365 days at FBA triggers long-term storage fees. One panic-driven over-order can sit and rack up fees for a year.
Fix
Cap order quantity at (lead + safety + 60–90 days cover). If days of supply ever exceeds 180, slow restocking before adding more.
Using one velocity for all seasons
Why it matters
A 60-day reorder point sized on summer velocity will stock you out in Q4. Velocity doubles or triples for many SKUs in Nov–Dec.
Fix
Recompute your reorder point monthly, and bump daily sales for the next 4–8 weeks before Q4 starts (Aug–Sep latest). Plan the Q4 inbound by late summer.
Pro tips
How experienced sellers restock
Practical ways to turn these four numbers into bulletproof restocking.
Decompose lead time honestly
Total lead time = manufacturing + transit + Amazon receive. Most stockouts come from underestimating the FBA receive step — pad it with a couple of days.
Set safety stock from variability
If daily sales swing ±30%, your safety stock should cover at least the high end of that range. Steady SKUs can run lean; volatile ones need a real buffer.
Treat 28 days of supply as a hard floor
Cross under it and Amazon adds the low-inventory-level fee per unit. Expediting shipping is usually cheaper than paying the fee for a month.
Recompute monthly + before Q4
Velocity drifts. Re-run the calculator on the first of each month and again in August/September to size Q4 orders early.
Pace orders to 60–90 days of cover
Order quantity that covers 60–90 days after arrival is the sweet spot — long enough to avoid constant reordering, short enough to dodge long-term storage.
Sync with your ad plan
Ramping ad spend lifts velocity, so the reorder point shifts up. Re-check the calculator whenever your PPC plan changes meaningfully.
Mind your IPI score and restock limits
Amazon's IPI score gates how much you can send. Low IPI = capped inbound — restock smaller and more often instead of one big shipment.
Who uses this
Built for these restocking decisions
Wherever an Amazon seller has to decide when to reorder, how much to order, or whether they can survive a sales spike.
Sellers planning the next restock order
Get reorder timing and the exact order quantity for an SKU about to cross its reorder point.
Operations managers across many SKUs
Run the calculator per SKU to standardise restock logic instead of relying on individual gut calls.
Owners preparing for Q4
Model a 2× or 3× velocity spike and size the Q4 inbound order by late summer — well before the fee zone hits.
Brands launching a new product
Pick the first reorder timing as soon as initial velocity is known, before the launch promo ends.
Agencies advising clients
Show clients a clear days-until-reorder + recommended quantity, not a vague "you should restock soon."
Sellers paying the low-inventory-level fee
Diagnose how far under 28 DoS you are and what order quantity restores you to a safe band.
Glossary
FBA inventory & restocking terms
The terms you'll meet in this calculator and across Amazon's Seller Central.
- Reorder Point
- The inventory level at which you should place your next order. = lead-time demand + safety stock.
- Lead Time
- Total days from placing an order to units being live at FBA — manufacturing + transit + Amazon receive.
- Safety Stock
- Extra inventory beyond lead-time demand, kept as a buffer against demand spikes or supplier delays.
- Days of Supply (DoS)
- How long your current FBA stock lasts at the current sales pace. Amazon calls this "Historical days of supply" in Seller Central.
- Days Until Reorder
- How many days until your inventory falls to the reorder point — the actionable date to place the next order.
- Low-inventory-level fee
- A 2024 Amazon surcharge added per unit when your historical days of supply falls below 28. Varies by size tier.
- IPI
- Inventory Performance Index — Amazon's 0–1000 score combining sell-through, stranded inventory, excess inventory, and in-stock rate. Low IPI gates your inbound limits.
- Restock Limit
- The maximum units of a storage type you can send to FBA. Tied to your IPI score and recent sell-through.
- Long-term Storage Fee (LTSF)
- Extra fee charged on inventory aged over 365 days at FBA. Combats stale stock.
- Inventory Turnover
- How quickly stock moves through the warehouse — measured in cycles per year. Higher is generally healthier.
- Months of Supply
- Days of supply divided by 30 — a quicker read for slow-moving SKUs.
- AOV
- Average Order Value — the typical revenue per order, used in profit projections per cycle.
Help & answers
Frequently asked questions
Everything you need to know about how the Amazon FBA Restock Calculator works.
01How do I calculate the reorder point for Amazon FBA?
Reorder point = (daily sales × lead time) + safety stock. Example: 10 sales/day, 60-day lead time, 14-day safety stock → (10×60) + (10×14) = 740 units. When FBA stock drops to 740, place the next order. This calculator also tells you how many days from today that will be.
02What is days of supply on Amazon FBA?
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.
03What is Amazon's low-inventory-level fee and how do I avoid it?
Introduced in 2024, this per-unit surcharge applies when your historical days of supply falls below 28. The fee varies by size tier (roughly 0.13 to 0.89 per unit in the marketplace currency). Treat 28 days as a hard floor — this calculator warns whenever you cross under it.
04How do I calculate safety stock for FBA?
Express safety stock as days of buffer above lead-time demand — typically 14–30 days — then multiply by daily sales to get units. Steady SKUs can run at 14 days; volatile categories, unreliable suppliers, or seasonal products warrant 30+ days.
05What is a typical lead time for Amazon FBA orders?
Total lead time = manufacturing + transit + Amazon receive. China-to-USA by sea is often 60–90 days; domestic can be 14–30 days. Always include Amazon's receive window (5–10 days) — underestimating it is the #1 cause of FBA stockouts.
06What is the difference between days of supply and days until reorder?
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.
07How much safety stock should I keep?
14 days for steady SKUs, 30 for volatile ones. Push higher for unreliable suppliers, sea transit, seasonal categories, or heavy PPC. Lower only for fast, reliable suppliers when cash flow is tight.
08Does this calculator account for units already in transit?
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.
09How is the recommended order quantity calculated?
Order Qty = daily sales × (lead time + safety + target cover) − current stock − units in transit. When the shipment arrives, total inventory equals (safety + cover) days of supply. Smarter than the common "1.5× lead-time demand" heuristic.
10What is Amazon's IPI score and how does it relate to restocking?
IPI (Inventory Performance Index) is Amazon's 0–1000 score combining sell-through, stranded inventory, excess inventory, and in-stock rate. A low IPI caps your inbound restock limits — clear stranded/excess stock and restock smaller before sending more.
11Can I use this calculator for a product launch?
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.
12How does this differ from the Amazon FBA Profit Calculator?
The FBA Profit Calculator works per-unit (what each sale earns after fees). This Restock Calculator works per-time (when to reorder and how much). They're complementary: profit-per-unit × units-per-cycle = profit per restock cycle, which this calculator shows directly.
13How often should I recalculate my reorder point?
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.
14How do I handle seasonality (Q4 spikes) with this tool?
For seasonal SKUs, bump "Average Daily Sales" to expected Q4 velocity (often 2–3× baseline) and re-run in August or September. That gives you the Q4 order in time to place it — Q4 lead times stretch as suppliers fill up, so plan early.
15What's the difference between "Order Now" and "Critical" status?
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.
16Is my data saved when I use this calculator?
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.
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Category
Ecommerce Seller Operations
Subcategory
inventory operations
Availability
Global · 9 markets
Price
Free forever
Topics
amazonfbarestockreorderinventorydays-of-supplylead-timesafety-stockcalculatorreorder-pointstockout-preventioninventory-management
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