How to know when and how much to reorder on Shopify

Short answer: Reorder a product when its on-hand quantity drops to its reorder point, the stock you'll sell during the time it takes a new order to arrive, plus a safety buffer. The formula is average daily sales × supplier lead time + safety stock. For how much to order, top back up to a target level. A practical rule is about two reorder points' worth of cover, minus what you already have on hand (and never below your supplier's minimum order quantity). Shopify's native admin tracks on-hand and now raises basic purchase orders, but it doesn't calculate these two numbers for you. That's the gap below, with the worked math.

The reorder point: how to know when to reorder

The reorder point is the on-hand level that should trigger a new order. Drop to it, and you place the order; the goal is for the last unit to sell just as the next shipment lands. Three inputs:

• Average daily sales: how many units of the SKU you sell per day, averaged over a recent window. Use real recent sales, not a gut number. (Parwise uses a trailing 30-day window.)
• Supplier lead time: days from placing the order to stock being on your shelf and sellable. Ask your supplier; include shipping and your own receiving time, not just their "ships in" promise.
• Safety stock: a buffer for the weeks demand runs hot or the shipment runs late. Without it, average lead time is a coin flip: half your reorders arrive late and you stock out.

Put them together:

reorder point = (average daily sales × lead time) + safety stock

The first term is your "lead-time demand": what you'll sell while waiting. Safety stock is the cushion on top. A simple, defensible way to set the cushion is half your lead time in extra days of cover. Long lead times deserve a bigger buffer because there's more time for something to go wrong. That's the default Parwise uses. You can override the lead time and safety days per SKU or set a store-wide default to match your actual supplier.

How much to order: the order-up-to method

The reorder point tells you when. It doesn't tell you how much. Order too little and you're reordering again next week; order too much and your cash is sitting on a shelf. The clean answer is an order-up-to level: decide the stock level you want to be at after the delivery lands, then order the difference.

order quantity = target level - on-hand - already-on-order

A practical target is twice the reorder point, which keeps roughly a full reorder cycle of cover in the building after you restock. So:

order quantity ≈ (2 × reorder point) - on-hand

Then floor it at your supplier's minimum order quantity (MOQ). If the math says 80 units but the supplier ships in cases of 100, you order 100. This is exactly the quantity Parwise pre-fills when it drafts a purchase order, so you're adjusting a sensible number rather than guessing from a blank field.

A worked example

Take one SKU, say a 500 ml water bottle.

• It sells 6 units a day on average (your trailing-30-day velocity).
• Your supplier's lead time is 14 days.
• Safety buffer: half the lead time = 7 extra days, so 6 × 7 = 42 units.

When to reorder:

reorder point = (6 × 14) + 42 = 84 + 42 = 126 units

When on-hand falls to 126, place the order. The 84 covers the two weeks you're waiting; the 42 keeps you standing if sales spike or the truck is late.

How much to order, restocking right at the reorder point (on-hand = 126):

order quantity ≈ (2 × 126) - 126 = 126 units

That's about three weeks of cover (126 ÷ 6 ≈ 21 days). If your supplier's MOQ is 150, you order 150 instead. Done: a number you can defend, not a hunch.

What Shopify shows you natively, and what it doesn't

Be fair about this: Shopify's native admin is more capable than it was. It tracks on-hand by location, and since absorbing Stocky's basics it can raise and receive basic purchase orders for free. Its Sidekick assistant can also answer one-off questions if you ask.

What it doesn't do is the everyday calculation above. As one merchant put it in an r/shopify Stocky-replacement thread:

"Shopify's native PO workflow covers the ordering and receiving side now, but it doesn't tell you when to reorder or how much. You still have to figure that out yourself."

That's the gap precisely. Native gives you the inventory numbers and the paperwork; it doesn't maintain a standing reorder point per SKU, recomputed from your real sales velocity, that flags a product before it runs out and pre-sizes the order. Sidekick can estimate on request, but a question you have to remember to ask isn't the same as a dashboard that's already done the math for every SKU, every day. For a store carrying more than a handful of products, "figure it out yourself" doesn't scale.

When a simple velocity reorder point isn't enough

The honest part: average daily sales × lead time + safety stock is the right tool for most steady-selling products, but it's a trailing average, and that's its blind spot. Cases where it under- or over-shoots:

• Strong seasonality. A trailing 30-day average doesn't see the holiday spike coming. Going into a known peak, raise the reorder point manually, or use a tool that does seasonal demand forecasting.
• Brand-new products with no sales history: velocity is zero or noisy until orders accumulate, so the first few reorder points are estimates. Set them by hand at first.
• A planned promotion or a viral moment: anything that breaks from the recent trend. The math reacts after the spike shows up in the window, not before.
• Multi-channel selling. If the same SKU sells on Amazon, eBay, or wholesale alongside Shopify, a Shopify-only velocity understates true demand. You need a single source of truth across channels.

For these, you want either a human override or a heavier demand-planning platform with machine-learning forecasts (Prediko, Inventory Planner, Cogsy and similar). That's a real, different category, priced accordingly. Transparent velocity math earns its keep on the long tail of steady sellers, and it has one advantage a black box doesn't: you can see exactly why it said what it said, and correct it.

How Parwise does this for you

Parwise is built to put these two numbers back in front of you the way the free Stocky used to, without the enterprise price tag:

• Low-stock alerts + an on-hand dashboard: the daily "what's about to run out" view. Free.
• A reorder point on every SKU, from your real sales velocity: average daily sales × lead time + safety stock, computed on a trailing 30-day window and shown, not hidden in a black box. Lead time and safety stock are editable per SKU or as a store-wide default, so you can set your real supplier lead time from day one. Free.
• A purchase order pre-filled with the recommended quantity: the order-up-to math above, floored at your supplier's MOQ, then a real receiving lifecycle: draft, send, partial-receive, receive/close, with supplier lead times. (Pro, $39/mo.)
• Flat pricing, $0 / $39 / $79, never metered by revenue, orders, SKUs, or locations. The number you budget this year is the number next year.
• No customer personal data. Parwise reads orders for SKU, quantity, and cost only. Never customer names, emails, or addresses.

The math is the same whether you run it by hand from the formulas above or let Parwise keep it current for every SKU. The point is to stop guessing, and to never again find out a best-seller is at zero from a customer.

FAQ

What is the reorder point formula? reorder point = (average daily sales × supplier lead time) + safety stock. The first part covers what you'll sell while waiting for the order; safety stock is a buffer for demand spikes and late deliveries. When on-hand drops to the reorder point, you place the order.

How do I calculate safety stock simply? A practical starting point is extra days of cover equal to about half your lead time, multiplied by your average daily sales. Longer lead times deserve a bigger buffer because there's more time for something to go wrong. For a 14-day lead time selling 6 units/day, that's 6 × 7 = 42 units. Tune it up if stockouts hurt more than holding cost.

How much should I reorder? Top back up to a target level rather than ordering a fixed amount. A common rule is about two reorder points of cover: order quantity ≈ (2 × reorder point) - on-hand, floored at your supplier's minimum order quantity. That keeps roughly a full reorder cycle of stock on hand after the delivery lands.

Can Shopify tell me when to reorder? Shopify's native admin tracks on-hand and now raises basic purchase orders, and Sidekick can answer one-off questions, but it doesn't maintain a standing, editable reorder point per SKU calculated from your sales velocity. That "when and how much" calculation is the gap apps like Parwise fill.

Does the reorder point use AI or machine learning? Parwise's reorder point is transparent velocity math (average daily sales over a trailing 30-day window × lead time + safety stock), not a machine-learning forecast. It's shown and editable so you can trust and adjust it. For seasonal or trend-based forecasting, a dedicated demand-planning platform is the better fit.