Lead time calculator with query rate
Queries lengthen the lead time more than the rate suggests, because every query means waiting for an answer. The calculator shows the average lead time per case for two cases: a query at the step, or a rework loop in which the step is repeated.
How the calculator works
Query at the step
With a query at the step, each pass adds on average query rate × effort in work and query rate × delay in waiting. The request worked example is filled in: 10 minutes of checking, 4 hours of waiting, 25% queries with 8 minutes of effort and 2 working days of waiting each. That gives 12 minutes of work and 480 minutes of waiting for this step.
Rework loop
If a case goes back after the answer and the step is processed again, that can happen several times. In the editor this is a connection back to the step; every connection that closes a loop counts there as a rework loop, without a separate flag. With a rate q the step is passed 1 ÷ (1 − q) times on average, 1.25 times at 20%. Processing and waiting of the step count that often, and the delay for the answer occurs q ÷ (1 − q) times on average.
Same calculation as the editor
The calculator builds the step as a small process – with a query rate or with a decision and a rework loop – and calculates it with the same function as the editor. The lesson Branches, queries and loops shows the full calculation with decisions; Lead time calculation explains the terms.
Frequently asked questions
Why does waiting for the answer weigh so much?
Handling a query often takes minutes, the answer days. Even a small rate therefore shifts the average lead time noticeably while working time barely rises.
Which unit does the calculator use?
Minutes of working time. A working day has as many hours as you enter under “Working hours per day”; weekends and public holidays do not count.
Which mode should I choose?
Query at the step if work simply continues after the answer. Rework loop if the case is checked again from the start after the answer and can wait again.