When you install the Reverse Planning app in Business Central, there are two background calculations you should run before you start working: the low-level code calculation and the rolled-up lead time calculation. Both make sure the app has the data it needs to plan correctly, especially if you have imported data from another system or recently upgraded.
The calculate low-level code function is standard Business Central functionality. It rebuilds the BOM tree across your items so the hierarchy is correct. Run it if the Dynamic Low-Level Code field in your manufacturing setup is not enabled, or if your data may be out of date.
The calculate rolled-up lead time function comes with the Reverse Planning app. It calculates the total lead time needed to supply an item including everything below it in the BOM hierarchy. You need this if you want the Simple MRP to plan each item based on its own rolled-up lead time instead of a fixed date range.
Both jobs can take a long time to run, so schedule them when the system is not heavily loaded.
Calculating low-level code in Business Central
The low-level code describes where an item sits in the BOM hierarchy. This is standard Business Central functionality, and in many cases your system already has correct low-level codes.
You can check this in your manufacturing setup. This is only relevant if you use manufacturing production orders. Look at the Dynamic Low-Level Code field. If it is check marked, you most likely already have the correct low-level codes in place.
There are situations where the codes are not correct. If you import data from another system or you upgrade, the low-level codes may be wrong. In that case, use the standard Calculate Low-Level Code function. When you run it, it goes through your items and builds the BOM tree for all items that are not yet calculated.
Be aware that this can take some time to run, so plan accordingly.
Calculating rolled-up lead time for Simple MRP
The Simple MRP in Reverse Planning gives you two ways to define the calculation period. You can either calculate from a fixed from-and-to date, or you can calculate using rolled-up lead time per item.
With a fixed date range, you set a start date and an end date, and the MRP calculates all your items in that period.
With rolled-up lead time, the calculation period adapts to each item. An item with a short lead time gets a short calculation window, and an item with a long rolled-up lead time gets a longer one. This helps you get the supplies right, because each item is planned far enough ahead to actually be supplied in time.
Before you can use rolled-up lead time in the MRP, you need to run the Calculate Rolled-Up Lead Time report. This report can take quite some time because it runs across all your locations and all your items. Run it when the system is not too loaded.
How rolled-up lead time differs between production and transfer
Once the report is done, you can look at the lead times on each item. A practical example shows why the rolled-up value matters.
Take item 1000. When you produce it on the production location, the direct lead time according to the routing is 14 days. But the rolled-up lead time is much longer, because it includes the time needed to supply everything below the item in the hierarchy. In this case, supplying the full hierarchy takes around 63 days.
The same item behaves differently when it is a transfer item on another location. The direct lead time for the transfer is only one day. But the rolled-up lead time is around 64 days, because the item is transferred from the production location, so it still depends on the full production hierarchy underneath it.
What to do after installing Reverse Planning
After installing the app, run these two jobs:
- Calculate Low-Level Code – the standard Business Central function that rebuilds the BOM tree.
- Calculate Rolled-Up Lead Time – the Reverse Planning function that calculates total supply lead time per item.
Both can run for a while, so do it when the system has capacity. Once they are done, the Simple MRP has the correct hierarchy and lead time data to plan your items accurately.
Q&A
What do I need to calculate after installing the Reverse Planning app?
You should calculate low-level code and rolled-up lead time if they are not already correct in your system. The low-level code calculation is standard Business Central functionality, and the rolled-up lead time calculation comes with the Reverse Planning app.
How do I know if my low-level codes are already correct?
Go into your manufacturing setup and check the Dynamic Low-Level Code field. If it is check marked, you most likely already have correct low-level codes. This check is only relevant if you use manufacturing production orders.
When can low-level codes be incorrect?
Low-level codes can be incorrect if you import data from another system or if you upgrade. In those cases, run the standard Calculate Low-Level Code function to rebuild the BOM tree for all items that are not yet calculated.
What is the difference between a fixed date range and rolled-up lead time in Simple MRP?
With a fixed date range, you set a start date and end date, and all items are calculated for that period. With rolled-up lead time, the calculation window adapts per item, so items with short lead times get a short window and items with long rolled-up lead times get a longer one.
Why is the rolled-up lead time longer than the direct lead time?
The direct lead time is just the time to produce or transfer the item itself. The rolled-up lead time also includes the time needed to supply everything below the item in the BOM hierarchy. For example, an item with a 14-day production lead time can have a rolled-up lead time of around 63 days.
Why does the Calculate Rolled-Up Lead Time report take so long?
The report runs across all your locations and all your items, so it can take quite some time. Run it when the system is not too heavily loaded.