Comprehensive Calculator Guide
This calculator adds up order processing, production and shipping days to tell you when an order will arrive, and works out the reorder point: the stock level at which to order so you don’t run out before delivery. An order placed on 1 November 2026 with a 17-day lead time arrives on 18 November; at 40 units a day with 200 units of safety stock, reorder at 880 units.
Lead time and the reorder point
Lead time runs from placing the order to having the goods ready to use: processing, production if needed, then shipping and customs for imports. Knowing each stage shows what you can shorten.
Reorder point = daily usage × lead time + safety stock. Safety stock covers late suppliers and demand spikes, such as before Ramadan, Eid and the school year.
How to Use
- Enter the order date and the processing, production and shipping days.
- Add daily usage and safety stock for the reorder point (optional).
- Press “Work out the lead time” to see the lead time, arrival date and reorder point.
Formula Used
Lead time = processing + production + shipping | Arrival = order date + lead time | Reorder point = daily usage × lead time + safety stock
Practical Examples
- Example 1: made to order
- Ordered 1 November 2026: 2 + 10 + 5 = 17 days, arriving 18 November. At 40 a day with 200 safety stock: 40 × 17 + 200 = 880 units.
- Example 2: local stock
- 1 day processing and 2 delivery: 3 days, arriving 4 November. At 25 a day with 50 safety stock: 125 units.
Important Tips
- Get each stage’s time from the supplier in writing.
- Allow for public holidays and weekends.
- Revisit the reorder point when usage or suppliers change.
Common Mistakes to Avoid
- Leaving customs out of import lead times.
- Planning on the supplier’s best time instead of the average.
- Running no safety stock on seasonal products.
Frequently Asked Questions
- Lead time vs cycle time?
- Lead time is order to delivery; cycle time is the time to make one unit.
- How do I calculate the reorder point?
- Daily usage × lead time + safety stock: 40 × 17 + 200 = 880.
- How much safety stock?
- It depends on demand swings and supplier reliability; start with a few days’ usage and adjust.