--- title: "Your Suppliers Are Late: Planning Around Lead Time Variability | Stockful Blog" description: "Average lead time hides the delays that cause stockouts. How to plan for lead time variability so a late shipment doesn't empty your best sellers." url: https://stockful.app/blog/supplier-lead-time-variability-shopify locale: en --- [← All posts](https://stockful.app/blog) [Shopify](https://stockful.app/blog/tag/Shopify) # Your Suppliers Are Late: Planning Around Lead Time Variability Average lead time hides the delays that cause stockouts. How to plan for lead time variability so a late shipment doesn't empty your best sellers. 24 Aug 2026 · 3 min read Ask most merchants their supplier lead time and you get a single number. “About three weeks.” That one number, treated as fixed, is where a surprising share of stockouts are born. You do not really have a lead time. You have a range. Sometimes the order lands in 14 days, sometimes it takes 35. Plan against the middle of that range, and you will be late roughly half the time, usually at the worst possible moment. ## Why lead time is so variable Lead time is the sum of a chain, and every link can slip: your supplier’s production queue, raw material availability, freight and shipping, customs and port delays, and seasonal squeezes like Chinese New Year when factories close and everything backs up. It also drifts with how busy your supplier is, which is rarely constant. A single average smooths all of that into a calm-looking figure that does not describe any real shipment. ## What to measure instead Stop quoting an average and start tracking the actual gap between when you place each order and when it arrives. Across a handful of orders, three things matter: - **The average,** as a baseline. - **The spread,** how much your lead time varies from order to order. This is the number that should change how you plan. - **The worst recent case,** because that is what a peak-season order is likely to hit. The spread is the part your buffer has to absorb. A supplier who always delivers in 14 days needs almost no protection. A supplier who delivers in anywhere from 14 to 40 needs a lot, or a backup. ## How variability feeds the rest of your planning Lead time is not an isolated setting. It flows into everything downstream. Your reorder point uses lead time to decide when to order. Feed it the average and your reorder timing is quietly optimistic, which is exactly the trap covered in [why the reorder point formula breaks for DTC](https://stockful.app/blog/reorder-point-formula-problems-dtc-shopify). Your safety stock should scale with lead-time variability, not just demand variability, so a flaky supplier earns a bigger buffer than a reliable one. That is the other half of the picture in [how much safety stock is enough](https://stockful.app/blog/how-much-safety-stock-shopify). ## Practical moves - **Record received dates** on every purchase order, so you build real lead-time history instead of relying on a vague sense of “about three weeks.” - **Set expectations per supplier.** One supplier’s reliability should not penalise another’s products with a blanket lead time. - **Protect critical items.** For A items with unreliable suppliers, hold more buffer or line up a second source. - **Order earlier into known squeezes,** like the run-up to Chinese New Year or peak season, when lead times predictably stretch. ## How Stockful helps In Stockful, lead time is a per-SKU setting that feeds your reorder recommendations, so the timing reflects each product’s real supply situation. You can also mark a supplier’s closed periods, such as a Chinese New Year shutdown, so reorder timing accounts for the gap instead of assuming the supplier can ship on your usual schedule. AI threshold suggestions propose a lead time per SKU based on your history, and incoming stock tracking shows you what is genuinely in transit, so you are planning against what is actually coming rather than a hopeful estimate. Safety stock does the rest. Stockful computes it statistically from your chosen service level, and it scales with lead-time variability as well as demand variability - so a flaky supplier automatically earns a bigger buffer than a reliable one, without you maintaining the numbers by hand. It is part of the same [self-tuning forecasting engine](https://stockful.app/shopify-demand-forecasting) that sizes your reorder quantities. A late supplier is not always avoidable. Being surprised by one is. Measure the spread, not just the average, and build your buffers around the variability that has always been there. _Get started free at _[_stockful.app_](https://stockful.app)_. Stockful uses your real lead times per SKU to time reorders and size buffers._ **More from Stockful:** - [How much safety stock is enough?](https://stockful.app/blog/how-much-safety-stock-shopify) - [Why the textbook reorder point formula breaks for DTC brands](https://stockful.app/blog/reorder-point-formula-problems-dtc-shopify) - [The true cost of a stockout on Shopify](https://stockful.app/blog/true-cost-of-stockouts-shopify) **Try Stockful on your Shopify store** Daily inventory history, forecasting, reports and an AI assistant. Free 14-day trial. [Start free trial](https://apps.shopify.com/stockful-inventory-management?utm_source=stockful-website&utm_medium=website&utm_campaign=blog&utm_content=article-cta)