Amazon Inventory Reorder Calculator

Managing inventory is one of the biggest challenges for e-commerce sellers. Our free Inventory Reorder Calculator helps you find the right time to reorder stock so you never run out or over-order again.

Inventory Reorder Calculator

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Inventory Reorder Calculator

Q: What is the reorder point formula?

The reorder point (ROP) is the stock level at which you should place your next purchase order to avoid stockouts. Formula: ROP = Daily Sales Rate × (Lead Time + Buffer Days). Example: If DSR = 20 units/day, Lead Time = 25 days, Buffer = 5 days, then ROP = 20 × (25 + 5) = 600 units.

Q: How many buffer days should I use?

Buffer days protect you from delays (supplier, customs, shipping). A common starting point is 5–7 days. Reduce to 3–4 for very reliable suppliers; increase to 10+ during peak seasons or if shipping is frequently delayed.

Q: Can this calculator work for Shopify, Flipkart, or other platforms?

Yes. The reorder point logic is universal across Amazon, Shopify, Flipkart, Etsy, and D2C sites. You balance sales velocity (DSR) against lead time so new stock arrives before you run out.

Q: What happens if I don’t reorder at the right point?

Reordering too late risks stockouts, lost sales, and lower visibility/rank on marketplaces. Reordering too early ties up cash flow and can increase storage costs. Hitting the reorder point helps balance both risks.

Q: How can I calculate my Daily Sales Rate (DSR) accurately?

Use your recent sales history, typically the last 30 days: DSR = total units sold ÷ 30. For seasonal items, consider a 60–90 day window or adjust based on expected demand. Pull figures from your platform’s analytics (e.g., Amazon Business Reports, Shopify Analytics).

Avoid stockouts by knowing exactly when to place your next order.

Inputs

Current Inventory (units)

Daily Sales Rate (units/day) Tip: use your 30-day average sales.

Lead Time (days) Production + shipping + inbound to FC (calendar days).

Buffer Days Extra protection for delays (start with 5–7).

* Estimates only. Does not include seasonality or PO minimums.

How to Use the Inventory Reorder Calculator

Step-by-step instructions:

1. Enter your current inventory.
2. Add your average daily sales rate.
3. Input your supplier lead time (production + shipping).
4. Add a few buffer days for safety.
5. Click Calculate to see when you should reorder.

Why Is the Reorder Point Important?

Running out of stock can cause:
– Lost sales
– Lower Best Seller Rank
– Missed Amazon Prime eligibility

Ordering too early means:
– Tied-up cash flow
– Higher storage costs

The reorder point formula balances both risks.

Glossary of Terms:

Current Inventory (units)
The number of units you currently have in stock and available to sell.

Daily Sales Rate (DSR)
The average number of units you sell per day.
👉 Best practice: calculate this using your last 30 days of sales.

Lead Time (days)
The total time it takes for new stock to arrive, including:

– Supplier production time
– Shipping/transit
– Amazon/warehouse check-in

Buffer Days (days)
Extra days added on top of lead time to protect against unexpected delays (holidays, customs, supplier issues). A typical buffer is 5–7 days.

Reorder Point (ROP)
The stock level at which you should place your next purchase order.
👉 Formula: ROP = DSR × (Lead Time + Buffer Days)
When inventory reaches this point, you need to reorder to avoid stockouts.

Days of Cover
How many days your current inventory will last, given your average daily sales.
👉 Formula: Days of Cover = Current Inventory ÷ DSR

Urgency Delta (units) (a.k.a. Stock Cushion)
The difference between your current inventory and the reorder point.

– Positive = you’re safe (extra units above ROP)
– Zero = you’ve just hit ROP (time to reorder)
– Negative = you’re already below ROP (urgent reorder needed)

FAQs About Inventory Reorder Point

What is the reorder point formula?

The reorder point (ROP) tells you the exact stock level at which you should place your next purchase order to avoid running out of inventory.

👉 Formula: ROP = Daily Sales Rate × (Lead Time + Buffer Days)

For example, if you sell 20 units per day, your supplier’s lead time is 25 days, and you add 5 buffer days, then:
ROP = 20 × (25 + 5) = 600 units.

This means when your inventory falls to 600 units, you should reorder so that new stock arrives just before your current stock runs out.

How many buffer days should I use?

Buffer days are your “safety net” for unexpected delays like supplier slowdowns, customs clearance, or shipping disruptions. Most sellers use 5–7 buffer days as a starting point. However:

– If your supplier is very reliable and ships quickly, you may reduce to 3–4 days.
– If your products are imported internationally or shipped during peak seasons (e.g., Q4), you may increase to 10+ days.

Always adjust buffer days based on your own risk tolerance and supply chain history.

Can this calculator work for Shopify, Flipkart, or other platforms?

Yes — the logic of reorder points is universal. Whether you sell on Amazon, Flipkart, Shopify, Etsy, or your own website, the principles are the same. You need to balance your sales velocity (DSR) against your lead time to ensure you don’t run out of stock. This calculator works across all sales channels.

What happens if I don’t reorder at the right point?

If you reorder too late:

– You may face stockouts, leading to lost sales and disappointed customers.
– On platforms like Amazon, this can also harm your Best Seller Rank (BSR) and visibility.

If you reorder too early:

– You tie up cash flow in inventory that sits in storage longer than necessary.
– You may also pay higher storage fees, especially for bulky products.

The reorder point formula helps you strike the right balance.

How can I calculate my Daily Sales Rate (DSR) accurately?

The most reliable way is to look at your sales history over the past 30 days and divide total units sold by 30.

👉 Example: 900 units sold in 30 days = 30 units/day.

For seasonal products, use a longer window (60–90 days) or adjust based on upcoming demand spikes. You can also use sales reports from your platform (Amazon Business Reports, Shopify Analytics, etc.) to calculate this automatically.