Inventory Reorder Calculator

Know when to reorder and how much, based on sales velocity and lead time.

🎁 Free

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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.

This free Inventory Reorder Calculator helps Amazon sellers calculate the exact Reorder Point (ROP) and see a clear status: “Reorder now” or “Safe for X days.”

How to use this calculator

1. Enter Current Inventory (units available to sell).
2. Enter Daily Sales Rate (DSR) – use a 30-day average if possible.
3. Enter Lead Time – production + shipping + FC receiving (calendar days).
4. Add Buffer Days – start with 5–7 to absorb delays.
5.Click Calculate to see ROP, Days of Cover, and your status.

Formulas

Reorder Point (ROP) = DSR × (Lead Time + Buffer Days)

Days of Cover = Current Inventory ÷ DSR

Inputs & outputs (at a glance)

Inputs

Current Inventory — total sellable units.
Daily Sales Rate (DSR) — average units/day.
Lead Time (DSR) — days from PO to sellable inventory.
Buffer Days — extra days to avoid stockouts.

Outputs

Reorder Point (units) — when to place the next PO.
Days of Cover (DSR) — how long stock lasts at current DSR.
Status — Reorder now or Safe for now (+ ETA to ROP).
Urgency Delta — Inventory − ROP (above/below target).

Worked example

Inventory: 850 units
DSR: 32 units/day
Lead Time: 18 days
Buffer: 7 days
Lead + Buffer: 25 days
ROP: 32 × 25 = 800 units
Days of Cover: 850 ÷ 32 = 26.6 days
Status: Safe for now — ~1 day until ROP
Urgency Delta: +50 units above ROP

Tips & edge cases for Amazon sellers

Seasonality: Increase DSR and/or buffer during festivals and Q4.
MOQ constraints: If MOQ > delta, order MOQ and adjust buffer next cycle.
Multiple inbound shipments: Subtract confirmed inbound units from the PO quantity you plan (not from ROP).
FC delays: Add 2–5 buffer days if your FC receives slowly.
Promos: If running a promo that lifts DSR, re-calculate beforehand.
Low-velocity SKUs: Use a longer DSR window (60–90 days) to smooth volatility.