Running out of a bestseller isn’t just a lost sale — it’s lost ad spend, a dented search ranking once the listing goes out of stock, and a customer who may buy from a competitor instead. The fix is cheap and mostly automatic: set a reorder threshold for each product and let your store platform (or a connected automation tool) email, text, or Slack you the moment inventory crosses it.
Table of Contents
This guide walks through how to turn on low stock alerts on the most common store platforms, how to pick a threshold that actually gives you enough lead time to reorder, and the mistakes that make alerts useless (too noisy, too late, or ignored entirely).
Quick Answer
Set a ‘low stock threshold’ (a reorder point) for each product — or each variation, if you sell in sizes or colors — in your store platform’s inventory settings, then turn on the built-in notification or connect an automation (like Shopify Flow) to email or message you when stock drops below that number. Shopify, WooCommerce, and BigCommerce all support this natively, including variant-level thresholds and triggers; third-party apps are only worth adding for extras like SMS/Slack alerts, grouped digests, or multi-location demand forecasting.
Set Your Reorder Threshold Before You Turn On Alerts
A low stock alert is only useful if it fires early enough to actually reorder before you sell out. Start by calculating a rough reorder point for each product: figure out how many units you typically sell in the time it takes your supplier to restock (lead time), then add a small buffer for demand spikes. A product that sells a dozen units a week with a two-week supplier lead time needs a much higher threshold than one that moves one unit a month.
Don’t use one global number for every product. A $15 phone case and a $400 appliance shouldn’t share the same ‘5 units left’ trigger — the appliance needs a higher buffer relative to how rarely it sells, and the phone case can run closer to zero without much risk. If you sell variants (sizes, colors), set thresholds per variation where your platform allows it, since a popular size can sell out while the overall product still shows plenty of stock. Review and adjust thresholds every quarter or after a big sales event, since demand patterns shift.
How to Turn On Alerts, Platform by Platform
Shopify: the fastest native route is Shopify Flow, included free on Shopify’s standard paid plans (its lowest-tier Starter plan doesn’t support it). In Flow, use the ‘Get notified by email when product variant inventory is low’ template, set your threshold and recipient email (or route it to Slack), and turn it on — no coding required. Flow’s inventory triggers fire per variant, so a product with several variants can generate a separate alert for each one that crosses the line. You can also just sort your Products list by inventory quantity to eyeball what’s running low, though that’s manual rather than automatic.
WooCommerce: go to WooCommerce > Settings > Products > Inventory for your store-wide defaults — a ‘Low stock threshold’ field, a separate ‘Out of stock threshold’ field, and a field for the notification recipient email address(es). For products sold in variations, open the product, go to the Variations tab, select a variation, and check ‘Manage stock’ to give that specific variation its own quantity and low stock threshold — do this at the variation level, not the parent product, since enabling ‘Manage stock’ on the parent instead pools one shared quantity across every variation. If you leave a variation’s threshold blank, WooCommerce falls back to the product-wide or store-wide default. Either way, WooCommerce emails your chosen address automatically whenever stock drops below the relevant threshold. This built-in notification isn’t very customizable in appearance, so if you want nicer formatting, SMS, or grouped digests, a plugin adds that flexibility.
BigCommerce: inventory notification emails can be configured per product in the product’s inventory settings (or in bulk via the API), letting you set a stock level that triggers an alert to a specified email address, such as yourself or a supplier. BigCommerce’s App Marketplace also has dedicated stock-alert apps if you need alerts sent to multiple people or on a recurring digest.
Square Online and other smaller platforms: look for an ‘inventory alerts’ or ‘low stock’ toggle under your item/inventory settings — most modern platforms now offer at least a basic email trigger. If yours doesn’t, a lightweight workaround is to export your inventory report on a schedule and scan it, or connect your store to a free automation tool (Zapier, Make, or the platform’s own Flow-style builder) that checks stock levels and messages you directly.
Tips and Common Mistakes
Don’t set every threshold to the same number just to save time — mismatched thresholds are the most common reason low stock alerts get ignored, because half of them fire too early (noise) and half fire too late (useless). Route alerts to a channel someone actually checks daily, like a dedicated Slack channel or a filtered inbox label, rather than a general inbox where they’ll get buried. If you sell through multiple sales channels (your own site plus a marketplace like Etsy or Amazon), make sure your alert source is tracking combined inventory, not just one channel’s count, or you’ll get blindsided by sales happening elsewhere. Finally, revisit thresholds after any big promotion or seasonal spike — a reorder point set for normal demand will fire far too late during a rush.
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Frequently Asked Questions
Do I need a paid app to get low stock alerts?
No. Shopify (via Flow), WooCommerce, and BigCommerce all include free, built-in ways to trigger a low stock email, including per-variant thresholds. Paid apps are mainly worth it for extras like SMS/Slack alerts, grouped digests, or multi-location demand forecasting.
What’s a good low stock threshold to start with?
A reasonable starting point is your average weekly sales for that product multiplied by your supplier’s lead time in weeks, plus a small buffer. Adjust it after watching how it performs for a month or two — if you keep selling out before the alert fires, raise it; if you’re reordering way too early, lower it.
Can I set different stock alerts for different sizes or colors of the same product?
Yes. In WooCommerce, enable ‘Manage stock’ on each variation (not the parent product) to give it its own quantity and low stock threshold. In Shopify, Flow’s inventory triggers already fire per variant, so each size or color can be tracked and alerted on separately.
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