Lead Time Buffer Calculator

Your lead time is not the number your supplier quotes on the phone. That's just factory time. The real lead time is supplier build plus ocean or air freight plus port clearance plus Amazon's inbound receiving, which in a bad month is the longest leg of the trip.

This tool adds those pieces: supplier lead time, shipping transit, and a port or clearance buffer you set for the unknowns — customs holds, trucking delays, the warehouse queue. The total is the clock that starts the moment you place the PO.

Then it asks for your average daily sales and works out the coverage you need: daily sales times total lead time. That's how many units have to be in stock (or in flight) the whole time you're waiting. Compare it to your reorder point. If your reorder point is lower than the coverage needed, you will stock out before the next batch lands, and no promotion can fix an empty listing.

Add extra buffer for the calendar. Chinese New Year shuts most of southern China's factories for two to three weeks, and the weeks around it jam the ports. If you source from there, build that into the buffer every January, or watch your best SKU go dark in March.

The point isn't precision. It's not forgetting a leg. Most "surprise" stockouts were just a lead time someone calculated too short. Add the buffer, set the reminder, and place the PO while you still have room.