How to Calculate Lead Time for Shopify Inventory

Lead time is one of those concepts that's simple to understand but easy to get wrong. It's the time between placing an order with your supplier and having the product in your hands, ready to sell. Every day you underestimate lead time is a day closer to a stockout. Every day you overestimate it is a day of carrying extra inventory you didn't need yet.

Getting lead time right is the foundation of accurate inventory forecasting — and it works hand-in-hand with choosing the right sales period to calculate accurate demand. Here's how to calculate lead time properly.

What Lead Time Actually Includes

Most merchants think of lead time as "shipping time." It's more than that. True lead time covers the entire journey from order to shelf.

Add all of these up, and your actual lead time is often significantly longer than the "shipping time" your supplier quotes. A supplier who says "ships in 5-7 days" might have a true lead time of 12-14 days once you account for processing on both ends.

How to Calculate Your Actual Lead Time

Step 1: Track Your Last 3-5 Orders

For each supplier, look at your recent purchase orders. Note two dates: the date you placed the order and the date the products were available to sell in your store. The difference is your actual lead time. If you want to understand how lead time fits into the bigger picture, our guide on the inventory lifecycle from purchase order to reorder walks through the full process.

Step 2: Calculate the Average

Don't rely on a single order — there's always variability. Average your last 3-5 orders to get a more reliable number. For example:

• Order 1: 18 days
• Order 2: 14 days
• Order 3: 21 days
• Order 4: 16 days
• Order 5: 15 days

Average: 16.8 days → round up to 17 days

Step 3: Round Up, Not Down

When setting lead time in your forecasting tool, it's always better to round up. If your average is 16.8 days, use 17 or even 18. The cost of having safety stock arrive a day early is negligible. The cost of running out because your lead time estimate was a day short can be significant.

Lead Time Varies — And That's Normal

Lead time isn't a fixed number. It changes based on:

Season. Lead times tend to increase during peak seasons (Q4 for most retailers) when suppliers and shipping carriers are handling higher volumes. A supplier with a 2-week lead time in March might take 3-4 weeks in November.

Order size. Larger orders may take longer to fulfill, especially if the supplier needs to produce items.

Supplier location. Domestic suppliers might have 5-10 day lead times. Overseas suppliers (China, India, Europe) can range from 3-8 weeks including shipping and customs.

Shipping method. Air freight is faster but expensive. Ocean freight is cheaper but adds weeks. The method you choose directly affects your lead time.

Setting Lead Time Per Product

Not all products have the same lead time, even from the same supplier. Some items are stocked and ship quickly; others are made to order.

In Sensible Forecasting, you set a default lead time in Settings that applies to all products. Then, for products with different lead times, you can override the default in the product detail view. This is especially useful when you source from multiple suppliers with different turnaround times.

For example, you might set your default lead time to 14 days (your main domestic supplier), then set it to 35 days for specific products you import from overseas.

How Lead Time Affects Your Reorder Point

Your reorder point is when you need to place an order so that new stock arrives before current stock runs out. Here's the formula:

If a product sells 3 units per day, your lead time is 14 days, and you keep 7 days of safety stock, you need to reorder when stock hits 63 units.

When your stock drops to 63 units, it's time to order. Sensible Forecasting calculates this automatically for every product and surfaces the ones that are at or near their reorder point.

Common Lead Time Mistakes

Using Supplier-Quoted Shipping Time

Suppliers quote their processing and shipping time, not your total lead time. They don't account for the time between when you realize you need to order and when you actually place the order, nor do they account for your receiving and processing time.

Not Updating Lead Times

Lead times change over time. A supplier that used to deliver in 10 days might now take 15 due to increased demand or operational changes. Review and update your lead times at least quarterly.

Using the Same Lead Time for All Products

If you source from multiple suppliers, each product (or product group) should have its own lead time. Using a single default means some products will be underestimated and others overestimated.

Ignoring Seasonal Variation

Your August lead time is probably not your November lead time. If you know from experience that Q4 adds a week to your deliveries, increase your lead time setting heading into the holidays and reduce it afterward.