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Inventory Forecasting Basics for Amazon Sellers (Toolkit Guide)

Learn how to forecast Amazon inventory using sales velocity, lead times, safety stock, and reorder points. Includes a practical framework and downloadable checklist to help sellers avoid stockouts and excess storage fees.

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Written by Denis
Updated over 2 weeks ago

📦 Overview

Inventory forecasting is the practice of predicting how much stock you’ll need and when it should arrive at Amazon fulfillment centers. Accurate forecasting helps sellers avoid costly stockouts, unnecessary storage fees, and missed Buy Box opportunities.

In this guide, you’ll learn a practical, Amazon-specific framework for forecasting inventory with confidence—plus how to turn it into a repeatable process using a downloadable checklist.

👤 Who This Is For

Beginner sellers

  • 🚀 Getting started with Amazon FBA or FBM

  • 🧭 Want a disciplined way to plan restocks instead of guessing

Experienced sellers

  • 📦 Managing multiple SKUs or seasonal demand

  • 💰 Optimizing cash flow, storage limits, and reorder timing

🧠 Key Concepts You Need to Know

  • 📈 Sales Velocity — Average units sold per day for a SKU

  • ⏱️ Lead Time — Time from placing a purchase order to inventory being available for sale

  • 📆 Days of Cover (DOC) — How long current inventory will last at the current sales pace

  • 🛡️ Safety Stock — Extra inventory held to absorb demand or supply variability

  • 🎯 Reorder Point — Inventory level that signals when it’s time to reorder

  • 🧰 Inventory Planning Tools — Systems that help prioritize restock decisions using real data

✅ Inventory Forecasting Checklist (Toolkit)

To make this framework easier to apply, we’ve created a downloadable Inventory Forecasting Checklist you can use every time you plan a restock.

The checklist turns forecasting into a repeatable workflow—helping you:

  • Catch stockout risks early

  • Avoid over-ordering inventory you can’t send in

  • Stay aligned with Amazon’s restock and storage limits

👉 Download the checklist and follow along as you work through the steps below.

🧮 Step-by-Step Guide / Actionable Framework

📊 1. Calculate Average Daily Sales

  • Pull Units Ordered for the last 30–90 days from Seller Central > Reports > Business Reports

  • Exclude unusual spikes (e.g., one-off promotions or stockout recovery)

Pro Tip: Compare 7-day, 30-day, and 90-day averages to spot demand shifts early.

🚚 2. Estimate Supply Lead Time

  • Include supplier production, shipping, and Amazon receiving time

  • Account for inbound processing delays at Amazon

Common Pitfall: Only counting supplier production time.

Pro Tip: Add a 7–14 day buffer during peak seasons like Q4.

🛡️ 3. Set Safety Stock

  • Start with 10–20% of monthly sales

  • Increase safety stock for overseas sourcing or volatile demand

📐 4. Calculate Your Reorder Point

Reorder Point = (Avg Daily Sales × Lead Time) + Safety Stock

Track this using Available + Inbound Inventory, not just on-hand units.

🧰 5. Use Inventory Forecasting Tools Effectively

Structured tools reduce manual errors by calculating restock needs using real sales and inventory data.

For example, the Seller Labs' Restock App calculates recommended reorder quantities using:

Need = [(Target Days of Stock × Amount Sold in 30 Days) / 30] – Current AFN Inventory

This helps sellers estimate how much inventory to reorder based on recent performance and desired stock coverage.

Pro Tip: Pair tool recommendations with seasonality, promotions, and supplier constraints.

🏪 Real-World Examples or Scenarios

Example 1: New FBA Seller

  • 👤 Profile: First-time seller with one product

  • ❗ Problem: Multiple stockouts in the first 60 days

  • 🔧 Action: Used 30-day sales velocity and added 15% safety stock

  • ✅ Result: Consistent availability and improved sales rank

Example 2: Established Brand (20+ SKUs)

  • 👤 Profile: Medium-sized brand with overseas sourcing

  • ❗ Problem: High storage fees and uneven inventory turnover

  • 🔧 Action: Forecasted per SKU using 60-day trends

  • ✅ Result: Lower storage costs and improved cash flow

⚠️ Common Mistakes to Avoid

  1. Forecasting by Gut Rather Than Data
    → Use sales velocity instead of intuition

  2. Ignoring Lead Time Variability
    → Build buffers for shipping and Amazon delays

  3. Over-Ordering to Avoid Stockouts
    → Use safety stock instead of bulk ordering

🎯 Expected Results

After applying this framework and checklist, sellers typically see:

  • Fewer stockouts and stronger Buy Box performance

  • More predictable cash flow

  • Lower long-term storage risk

  • Easier scaling as catalogs grow

❓ FAQs

How often should I update my forecast?
Monthly at minimum; weekly for fast-moving or seasonal SKUs.

What sales period should I use?
30–90 days that best reflect current demand.

Should forecasting change in peak season?
Yes—use larger buffers and longer lead times.

Do Amazon’s tools handle forecasting automatically?
They provide signals, but sellers still need to interpret trends and make decisions.

Where can I get reorder quantity recommendations?
Tools like the Restock App calculate them using sales and inventory data.

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