Planned Order Release Lead Time Calculator
MRP subtracts lead time from the need date to find when an order must start. If the lead time is wrong, every planned release is early or late. This calculator builds the lead time from its parts.
Your numbers
Available hours at the constraint after efficiency
Your results
A planning approximation. Calendar conversion uses a simple ratio and ignores holidays, shutdowns and overlap between operations. Use your ERP calendar for final dates.
Lead time vs order quantity
Sweeps Order quantity from 10 to 3000, holding your other inputs fixed.
Lead time analysis from real orders
Optional: compare planned lead times with actual order history in your ERP.
Optional. The tool and every export work without this. No spam.
How to use it
Enter the order quantity, the fixed time per order such as setup and paperwork, and the run time per unit. Add queue and move time, inspection and put-away, and any safety lead time. Select how many days per week the plant works. The result shows total working days and the calendar days before the need date to release the order. The chart shows how lead time grows with order size.
The formula
Total working days equal fixed time plus quantity times run hours divided by productive hours per day, plus queue, inspection and safety time. Calendar days are working days times 7 divided by working days per week, rounded up. Many ERPs store a fixed lead time and a variable lead time per unit separately, which matches this split. Entering the same two values in your item or routing data lets the system scale lead time with lot size.
Reading the result and common mistakes
If the non-run share is above half, most of the lead time is waiting rather than work, so shorter queues or smaller batches help more than faster machines.
- Using one fixed lead time for very different lot sizes.
- Counting calendar days where the ERP expects working days, or the reverse.
- Forgetting inspection or receiving time on purchased items.
- Stacking safety lead time at every BOM level.
- Taking nameplate hours rather than productive hours.
Frequently Asked Questions
What is the difference between fixed and variable lead time?
Fixed lead time is the part that does not change with lot size, such as setup, queue and inspection. Variable lead time scales with quantity, such as run time per unit. Separating them lets the system give a realistic lead time for both small and large orders.
Why does safety lead time matter?
It releases an order earlier than the pure calculation so that normal delays do not make it late. It reduces late deliveries but also raises stock and work in progress, so use it sparingly and not at every level of the BOM.
How are working days turned into calendar days?
Multiply working days by 7 and divide by working days per week. For example 10 working days on a 5-day week is 14 calendar days. This ignores holidays, so check the result against your plant calendar.
Does this work for purchased items?
Yes. Use the supplier lead time as the fixed time, set run time to zero, and add receiving and inspection time. If the supplier quotes calendar days, set working days per week to 7.
If you want lead times proposed from your actual shop order and receipt history, we can analyse that read-only from your ERP.
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