FBA Inventory Forecasting: The Science of Never Running Out
Stockouts kill your Amazon ranking, your Buy Box percentage, and your revenue. Here's how to forecast accurately.
The Basic Reorder Formula
Reorder Point = (Average Daily Sales × Total Lead Time) + Safety Stock
| Component | Calculation |
|---|---|
| Average Daily Sales | Last 30–90 day sales ÷ days |
| Total Lead Time | Production + Shipping + Prep + FC Check-in |
| Safety Stock | 14–30 days of average sales |
Lead Time Components
| Stage | Domestic Product | International Product |
|---|---|---|
| Production | 0 days | 21–42 days |
| Shipping to prep | 1–5 days | 25–45 days (ocean) |
| Prep/labeling | 1–3 days | 3–5 days |
| Ship to FBA | 2–5 days | 2–5 days |
| FC check-in | 3–7 days | 3–7 days |
| Total | 7–20 days | 54–104 days |
Seasonal Adjustment Factors
| Month | Adjustment | Reason |
|---|---|---|
| January | 0.7x | Post-holiday slowdown |
| February | 0.8x | Winter slowdown |
| March–May | 1.0x | Normal |
| June–August | 0.9–1.1x | Varies by category |
| September | 1.2x | Back to school |
| October | 1.5x | Pre-holiday buildup |
| November | 2.0–3.0x | Black Friday/Cyber Monday |
| December | 2.0–2.5x | Holiday peak |
Forecasting Methods
1. Simple Moving Average Average of last 30/60/90 days sales. Good for stable products.
2. Weighted Moving Average Recent sales weighted more heavily. Better for trending products.
3. Year-over-Year Compare same period last year with growth factor. Best for seasonal products.
Common Forecasting Mistakes
- Using too short a window — 7-day average is too volatile
- Ignoring seasonality — Q4 can be 2–3x normal volume
- Not accounting for promotions — Lightning Deals spike sales temporarily
- Forgetting FC check-in time — Can be 3–14 days during peak
- Ignoring competitor activity — New competitors affect your sales velocity
Tools for Forecasting
- Amazon's Restock Inventory tool — Good starting point
- Inventory management software — SoStocked, RestockPro
- Spreadsheet models — Custom formulas for your business
The Logistics Connection
Accurate forecasting means nothing if your shipping partner can't deliver on time. Work with a freight provider who guarantees consistent transit times to Amazon FCs. Indray Inc provides reliable FBA shipping with 98% on-time delivery.
