Lead Time Calculator
Add up the stages of an order to find total lead time — and the stock level that should trigger a reorder.
Three stages add up
Order processing, production, and transit combine into the total time from order to delivery.
Lead time drives reorders
Reorder before stock runs out: demand during the lead time plus a safety buffer.
What is lead time?
From order placed to order received
Lead time is the total elapsed time between placing an order and having it ready to use or sell. In a supply chain it is the sum of the stages an order passes through: the time your supplier takes to process and start the order, the time to produce it, and the time to ship it to you. As operations references such as Investopedia and APICS material explain, lead time is one of the most important numbers in inventory management, because it decides how early you must reorder to avoid running out.
Total lead time is a simple sum; the reorder point builds on it.
lead time = processing + production + transit; reorder point = daily demand × lead time + safety stockThe first formula adds the three stages into a single lead time in days, which the calculator also shows in weeks. The second turns that into an action: if you sell 50 units a day and it takes 20 days for a new order to arrive, you will burn through 1,000 units while you wait, so you should reorder once stock falls to that level — plus a safety stock buffer (here 100) to cover demand spikes or supplier delays. That total, 1,100 units, is the reorder point.
Your supplier takes 3 days to process an order, 10 days to produce it, and 7 days to ship it. You sell 50 units a day and keep 100 units of safety stock.
Add the stages
3 + 10 + 7 = 20 days of total lead time.Convert to weeks
20 ÷ 7 ≈ 2.9 weeks.Find demand during lead time
50 units/day × 20 days = 1,000 units.Add safety stock
1,000 + 100 = 1,100 units — reorder when stock hits this level.
Lead time is the hinge between buying too early and running out, and small changes ripple through your whole inventory plan.
Sets the reorder point
Longer lead times mean you must reorder earlier and hold more stock to bridge the wait.
Drives safety stock
Variable or unreliable lead times need a bigger safety buffer to avoid stockouts.
Affects cash and space
Shorter lead times let you order less, more often — freeing cash and warehouse space.
Shrinking any stage shortens the whole chain: a supplier who starts production a day sooner, a faster freight option, or pre-approved paperwork all cut the lead time and the stock you must carry. That is why reducing lead time, not just managing it, is a core goal of supply-chain work.
The total lead time is how long, on average, a replenishment order takes from click to shelf, shown in both days and weeks. The reorder point is the inventory level at which you should place that order so the new stock arrives just as you would otherwise run out — with the safety stock as a cushion. If your demand or lead time varies a lot, treat these as averages and lean on a larger safety stock. Recalculate whenever a supplier's times change, demand shifts, or you switch shipping methods, because the reorder point moves with all of them.
The arithmetic is exact; real supply chains are not.
Averages hide variability
This calculator uses average times and demand, but real lead times and sales fluctuate, and a single late shipment can cause a stockout even when the averages look safe. It also assumes the three stages happen in sequence with no overlap and ignores order-quantity effects, supplier minimums, and seasonality. Use the result for planning and reorder-point setting, and pair it with a safety stock sized to your actual demand and lead-time variability rather than relying on the averages alone.