Hello Shani,

A shop order manufacturing lead time is a combination of calculations based on the routings (machine setup times, run factors, labor setup time and run factors etc.).In addition to that the purchasing lead times for the component parts and the shop order lot size may also be considered for this calculation. The need dates are calculated according to this.

you can also use the routing window to calculate the manufacturing lead time for a specific part

Should be mentioned though, that the start date / finish dates of a shop order depends on how its operations have been scheduled rather than the lead time calculated for the routing alternate (even though the result is expected to be fairly equal of course).

The scheduling depends on a large number of parameters. I attach the help file where described. However also note that operations can be rescheduled in any way, even so that the shop order finish after its need date! (then classified as tardy)

Hi @Shani Fernando  ,

Further to the above, you could run the lead time calculation as below, specific to a part or the entire site depending on your requirement.

This can be done once you create the part structures and routings. So the lead time will be automatically taken into consideration at the point of creating the Shop Order.

Best Regards,

Dasuni

@Shani Fernando, when you create the Shop Order as Backwards Scheduling it decides Finish and Start Dates based on the Need Date.
Now, you may have defined lead times at Routing or Inventory Part windows but when creating the Shop Order at that point system takes the durations of each operations fetched to the Operation tab in the shop order, to calculate the order specific lead time. After accumulating the total duration of all the operations it gets the manufacturing lead time specific to that shop order. 
To decide the durations of operations there are many parameters (as mentioned by Björn above).
 

Hi @Tharindu Illangasinghe , @Björn Hultgren , @Dasuni Samarakoon , @Bhanuka Ranaweera,
 

Thank you very much for your explanations.
Now it is clear how the application calculates the lead time to manufacture the order.
 

Best Regards,
Shani