Your reorder point is daily sales multiplied by supplier lead time, plus a safety buffer. Sell eight units a day with a 14-day lead time and a week of cover, and you reorder when stock hits 168 units.
Why timing beats quantity
Most sellers think about how much to order and not when. The result is the same two failures on repeat: a bestseller out of stock for three weeks while a shipment crosses an ocean, or cash tied up in a slow mover that is now paying storage fees.
The Reorder Point Calculator gives you the trigger level and tells you how many days of stock you have left, which is the number worth checking weekly.
Setting safety stock
Seven to fourteen days of cover suits most small sellers. Increase it when your supplier is unreliable, when lead times swing unpredictably, or heading into a peak season. Decrease it for items where holding costs are high and running out briefly is survivable.
One correction people miss: use recent average daily sales for normal months, but switch to peak figures before a busy season. Averaging across a quiet spring will have you reordering far too late for the autumn run-up.
The cost of getting it wrong
Running out is worse than it looks on a marketplace. Out-of-stock listings lose rank and sales history, and recovering that position takes longer than the restock. Overstocking is quieter but expensive, particularly on Amazon where storage fees rise sharply in the final quarter and long-term surcharges apply to inventory that sits too long. We covered that in the FBA fees post.
Build it into a weekly habit
Once a week, check days of stock left on your top ten products. That single routine prevents most stockouts, and it takes about five minutes once your numbers are in one place.