Most FBA sellers reorder inventory the same way: gut feeling, a low-stock notification, or a panicked Slack message when the tracker hits single digits. It works — until it doesn't. A stockout kills your rank. A 200-unit overstock triggers storage fees. And in 2026, Amazon added a low inventory fee and a 3.5% fuel surcharge that changed the math on both ends of the spectrum.
Here's the reorder point formula that threads the needle — and the specific numbers you need to calculate it for your ASINs right now.
The Formula (It's Simple, But Most Sellers Skip It)
Your reorder point is the inventory level at which you place your next purchase order. Miss it and you stockout. Wait too long after it and you're overpaying for storage.
Reorder Point = (Daily Sales Velocity × Lead Time) + Safety Stock
Let's break down each piece.
Daily Sales Velocity
Pull your last 30 days of units sold from Seller Central → Reports → Business Reports. Divide by 30. That's your daily velocity. Use 60 days if your product is seasonal — it smooths out spikes.
Example: You sold 180 units in the last 30 days. Daily velocity = 6 units/day.
Lead Time
This is the total days from placing your PO to units being live in FBA. Include: supplier production time + transit time + Amazon receiving time (typically 5–10 days at the FC). If you're importing from overseas, a realistic lead time is 45–60 days. Domestic is 10–20 days.
Example: Overseas supplier = 50-day lead time.
Safety Stock
This is your buffer for surprises — delayed shipments, demand spikes, Amazon holding your inventory for inspection. A simple formula:
Safety Stock = Daily Velocity × (Max Lead Time − Average Lead Time)
If your average lead time is 50 days but your worst-case has been 65 days, your safety stock = 6 units × 15 days = 90 units.
Putting It Together
Reorder Point = (6 × 50) + 90 = 390 units
When your FBA inventory drops to 390 units, place the order. Not 200. Not 100. 390.
Why 2026's Fee Changes Make This More Important Than Ever
Amazon introduced two changes this year that directly punish bad inventory math:
- Low Inventory Fee: If you hold fewer than 28 days of cover for an ASIN, Amazon charges an extra per-unit fulfillment fee. For a standard-size item, this can add $0.32–$1.11 per unit. That's on top of the regular fulfillment fee.
- 3.5% Fuel Surcharge: Added to all FBA fulfillment fees. Small on a single unit; meaningful at scale.
- Aged Inventory Surcharge at 181 days: The penalty clock now starts earlier. Units sitting past 181 days get hit with additional storage charges before they even reach the 365-day mark.
The squeeze is real: Too lean = low inventory fee. Too heavy = aged inventory surcharge. Your reorder point formula is what keeps you in the profitable middle.
The "Days of Cover" Check
Run this number every week, not just when you're restocking:
Days of Cover = Units On Hand ÷ Daily Velocity
If you have 420 units and sell 6/day, you have 70 days of cover. That's healthy. Under 28 days triggers the low inventory fee. Over 180 days starts moving toward aged inventory risk.
Target range: 30–90 days of cover for most ASINs. Seasonal products may need more buffer heading into peak season.
When to Recalculate
Your velocity changes. Your lead times drift. Recalculate your reorder point:
- After any PPC campaign change (higher ad spend often lifts velocity)
- Before and after peak seasons (Q4, Prime Day, holidays)
- Any time your supplier changes production schedules
- After a ranking gain or loss — rank shifts change velocity fast
A Quick Tracker You Can Build in 10 Minutes
You don't need software for this. A spreadsheet with four columns does the job:
- ASIN / Product Name
- Daily Velocity (30-day average)
- Lead Time (days)
- Reorder Point (the formula output)
Update velocity monthly. Every week, check your FBA on-hand against the reorder point column. When you hit it, order.
Your one action today: Pull up your top 3 ASINs in Seller Central, calculate the daily velocity for each, and figure out what your current reorder point should be. If you're already below it — place the order.
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