How to Calculate Reorder Points for Your WooCommerce Store (And Stop Guessing on Restocks)

Most WooCommerce store owners manage restocking with a single number: a low-stock threshold that gets set once and never revisited. It works fine until it doesn’t — until a bestseller sells out for two weeks during its busiest month, or until a warehouse fills up with slow-moving stock that never should have been reordered. The problem isn’t inventory management software. It’s that most stores never do the math that tells them when and how much to reorder in the first place.

Here’s the actual math behind reorder points and safety stock, with real numbers, so you can stop guessing.

The Three Numbers You Actually Need

Before you can set a sensible reorder point for any SKU, you need three inputs:

• Average daily sales (sales velocity): units sold per day, averaged over a recent, representative period — usually the trailing 30 or 60 days, excluding one-off spikes like a flash sale.
• Lead time: the number of days between placing a purchase order with your supplier and having stock ready to sell, including any receiving and QC time.
• Demand and lead time variability: how much your sales and your supplier’s delivery times actually fluctuate week to week.

Most stores have the first number somewhere in their WooCommerce reports. Almost none track the third — and it’s the one that determines whether you stock out or sit on dead cash.

The Reorder Point Formula

The baseline formula is straightforward:

Reorder Point = (Average Daily Sales × Lead Time in Days) + Safety Stock

Say a SKU sells 8 units a day on average, and your supplier takes 12 days to deliver a new batch. Your lead time demand is 8 × 12 = 96 units. That’s the stock you’ll burn through while waiting on the next shipment — before you even add a buffer. If you reorder at exactly 96 units and anything goes even slightly wrong, you’re out of stock before the new inventory lands.

Calculating Safety Stock Properly

Safety stock is the buffer that absorbs the variability the baseline formula ignores. There are two common ways to calculate it:

The simple max-based method

Safety Stock = (Max Daily Sales × Max Lead Time) − (Average Daily Sales × Average Lead Time)

Using the earlier example: if your worst-case daily sales are 14 units and your worst-case lead time is 16 days, your max scenario is 14 × 16 = 224 units. Subtract the average lead time demand of 96, and your safety stock is 128 units. Your reorder point becomes 96 + 128 = 224 units. This method is easy to calculate from order history and works well for stores that don’t want to get into statistics.

The statistical method

For higher-volume SKUs, a standard-deviation-based formula gives a tighter, less wasteful buffer:

Safety Stock = Z-score × √(Lead Time) × Standard Deviation of Daily Sales

A Z-score of 1.65 targets roughly 95% service level (you’ll stock out on about 1 in 20 reorder cycles); 2.33 targets around 99%. If your daily sales standard deviation is 3 units and lead time is 12 days: Safety Stock = 1.65 × √12 × 3 ≈ 17 units. That’s a much leaner buffer than the max-based method produces, which matters a lot once you’re carrying this calculation across hundreds of SKUs and don’t want cash locked in excess stock.

Where WooCommerce Stores Usually Get This Wrong

• One threshold for every product. Setting a flat “reorder at 20 units” rule for the whole catalog ignores that a SKU selling 15 units a day needs a completely different buffer than one selling 1 unit a week.
• Ignoring seasonality. A reorder point calculated from October sales data will badly under-order for a product that triples in December. Recalculate lead time demand seasonally for anything with real seasonal swing.
• Treating supplier lead time as fixed. Lead times slip, especially with overseas suppliers. If you’ve never once measured your actual average and worst-case lead time (not the number the supplier quotes you), your safety stock is a guess dressed up as a formula.
• Static spreadsheets. A spreadsheet with reorder points calculated once, six months ago, is worse than no formula at all — it creates false confidence while the underlying sales velocity has already shifted.

Setting This Up in WooCommerce

WooCommerce’s native inventory settings let you set a “low stock threshold” per product under Product Data → Inventory, which triggers an email notification. That’s a fine starting point for a small catalog, but it’s manual: you calculate each threshold yourself, and nothing recalculates as sales velocity changes.

For catalogs beyond a few dozen SKUs, recalculating reorder points by hand every month doesn’t scale. This is one of the areas where agentic tools are actually useful rather than gimmicky — a tool like CommerceBird can continuously track sales velocity per SKU, recompute reorder points and safety stock as demand shifts, and flag or even draft purchase orders automatically instead of you re-running the math in a spreadsheet every few weeks.

Whether you automate it or not, the underlying discipline is the same: reorder points need to be SKU-specific and revisited on a schedule, not set once and forgotten.

A Practical Weekly Routine

If you’re doing this manually, an ABC classification keeps the workload manageable:

• A items (roughly top 20% of SKUs by revenue): review reorder points weekly. These are the products where a stockout actually hurts.
• B items (the next 30%): review monthly.
• C items (the long tail): review quarterly, or set a wide, conservative buffer and move on.

Track one metric alongside this: your back-order or stockout rate on A items. If it’s climbing, your safety stock is too thin or your lead time assumptions are stale — recalculate before you add more buffer blindly, since padding every SKU with extra stock just trades a stockout problem for a cash-flow problem.

The Takeaway

A reorder point isn’t a gut-feel number — it’s average daily sales times lead time, plus a safety buffer sized to how much your demand and your supplier’s delivery times actually vary. Calculate it properly for your top sellers first, revisit it on a schedule, and you’ll cut stockouts on your best products without tying up cash in slow movers you over-ordered out of caution.