Managing inventory is one of the biggest challenges for Amazon and e-commerce sellers. This free Inventory Reorder Calculator helps you find the right moment to reorder stock — so you never run out and lose ranking, and never over-order and tie up cash. Enter your current stock, sales speed, lead time, and a buffer, and it tells you your reorder point and how much runway you have. Everything runs in your browser; nothing is stored or sent anywhere.
How to use this calculator
- Enter your current inventory — the units you have available to sell now.
- Add your average daily sales rate — best taken from your last 30 days.
- Input your supplier lead time — production plus shipping plus warehouse check-in.
- Add a few buffer days — extra safety for delays, typically 5–7.
- Read the result — your reorder point, days of cover, and whether you're safe or need to reorder now.
- Reorder Point (ROP):
DSR × (Lead Time + Buffer Days) — the stock level at which to place your next order.
- Days of Cover:
Current Inventory ÷ DSR — how long your stock lasts at current sales.
- Stock cushion:
Current Inventory − ROP — positive means safe, negative means you're already overdue to reorder.
Why the reorder point matters
Running out of stock costs you lost sales, a lower Best Seller Rank, and can break Prime eligibility — damage that often outlasts the stockout itself. Ordering too early ties up cash flow and racks up storage fees. The reorder point balances both risks, so stock lands just before you'd otherwise run dry.
Worked example
Current inventory 800 units · daily sales 20 · lead time 25 days · buffer 5 days
ROP = 20 × (25 + 5) = 600 units. Days of cover = 800 ÷ 20 = 40 days.
→ Cushion = 800 − 600 = +200 units. You're safe for now; reorder when stock reaches 600.
Tips & edge cases
- Use a 30-day average for daily sales; for seasonal products, use 60–90 days or adjust for an upcoming spike.
- Increase your buffer in Q4 or when importing internationally — 10+ days is sensible during peak season.
- Reduce the buffer only if your supplier is fast and reliable.
- The logic is universal — it works for Amazon, Flipkart, Shopify, or your own store.
- Watch order minimums — your supplier's MOQ may mean ordering more than the cushion suggests.
Glossary
- Current inventory: units you have in stock and available to sell.
- Average Daily Sales (DSR): average units sold per day, ideally over the last 30 days.
- Lead time: total time for new stock to arrive — production, shipping, and check-in.
- Buffer days: extra days added to lead time to absorb unexpected delays.
- Reorder point: the stock level at which you should place your next order.
- Days of cover: how many days your current stock will last.
FAQs
What is the reorder point formula?
The reorder point is your daily sales rate multiplied by the sum of lead time and buffer days: ROP = DSR × (Lead Time + Buffer). When your stock falls to this level, place your next order so fresh inventory arrives just before you run out.
How many buffer days should I use?
Most sellers start with 5–7 days. If your supplier is fast and reliable you might use 3–4; for international imports or Q4 peak season, 10 or more is safer. Tune it to your own supply-chain history.
Can this work for Shopify, Flipkart, or other platforms?
Yes. Reorder-point logic is universal — Amazon, Flipkart, Shopify, Etsy, or your own website. You're balancing sales velocity against lead time, which applies to any channel.
What happens if I don't reorder at the right point?
Reorder too late and you risk stockouts, lost sales, and a lower Best Seller Rank. Reorder too early and you tie up cash and pay extra storage fees. The reorder point helps you strike the balance.
How do I calculate my Daily Sales Rate accurately?
Divide total units sold over the last 30 days by 30. For example, 900 units in 30 days is 30 per day. For seasonal products, use a 60–90 day window or adjust for expected demand.
Is my data saved anywhere?
No. Everything is calculated in your browser — nothing you type is uploaded or stored on any server.
