Free tool · For DTC brands on Shopify

Reorder Point & Safety Stock Calculator

Reorder too late and you stock out (or oversell); reorder too early and you tie up cash in a warehouse. Enter your own sales rate, supplier lead time, and how much both of those wobble, and this gives you the reorder point — the on-hand level at which to place the next order — and the safety stock buffer that protects your target service level.

Your numbers, for one SKU

Do this per product (or per variant). Everything updates instantly. Nothing is sent anywhere — this runs entirely in your browser.

Average daily sales — units of this SKU sold per day, on a normal day.

units/day

Supplier lead time — days from placing a PO to stock being sellable.

days

Daily sales variability (std. dev.) — your estimate: how much daily sales bounce around. Roughly a third to a half of average daily sales is common — adjust to your data.

units/day

Lead-time variability (std. dev.) — your estimate: how much your supplier's delivery time varies, in days. Enter 0 if it's rock-steady.

days

Target service level — % of reorder cycles you want to avoid a stockout. 95% is a common target; 99% costs a lot more buffer.

Current stock on hand — units you have right now. Optional — used only to tell you whether it's time to reorder. Enter 0 to skip.

units

Your reorder numbers

Reorder point

Safety stock

Expected demand during lead time avg daily sales × lead time	0
+ Safety stock buffer for demand & lead-time variability at your service level	0
= Reorder point	0
Safety stock as days of cover how many normal sales days the buffer alone buys you	0
Current stock on hand	—

Read this as a planning estimate, not a guarantee. It uses the standard reorder-point formula — reorder point = (average daily sales × lead time) + safety stock, where safety stock = Z × √(lead time × demand variance + avg sales² × lead-time variance) and Z is the service-level factor from the normal distribution. It assumes demand and lead time are roughly bell-shaped and independent; highly seasonal or spiky SKUs will need more judgement. Every number here comes only from the values you typed — tune the variability inputs to your own history.

How to read it

Reorder point — when on-hand stock drops to this number, place the next purchase order. It covers expected sales through the whole lead time plus the safety buffer.
Safety stock — the cushion that absorbs a good week of sales or a late shipment. Higher service level or more variability ⇒ bigger cushion.
Service level trade-off — going from 95% to 99% roughly doubles the safety stock for the same variability. Reliability costs cash tied up in inventory; pick the level that fits the SKU's margin.

Why a good reorder point still fails silently

A reorder point only works if the on-hand number it's compared against is true. In practice the inventory count in Shopify quietly drifts from what's on the shelf — a 3PL or ERP sync half-fails, a bundle decrements the wrong SKU, a return never restocks. When the number is wrong, the reorder trigger fires late (stockout) or the store keeps selling stock that isn't there (oversell). Nothing errors; you just find out from an angry customer.

How Ops Monitor catches this automatically

Ops Monitor connects to your Shopify (and 3PL/ERP) with read-only API keys and watches your inventory counts continuously — flagging sync drift, negative or impossible on-hand levels, and oversell risk, and alerting you by email or Slack the moment the number stops matching reality, so the reorder point you set here can actually be trusted.

It is read-only: it never writes to your store and never changes stock. It detects and alerts — it does not place orders or guarantee stock levels. One prevented oversell or stockout on a hero SKU is usually worth far more than the $149/month price.

See for yourself

Start watching your inventory counts in minutes with read-only keys — $149/month, self-serve, cancel anytime.

Start monitoring — $149/mo →

Not ready? Run the free, no-signup Ops Scorecard to see where your store is most exposed. Or have us hand-check one messy SKU/sync for you with the $29 one-time ops audit.