MRP Net Change vs Regenerative Run Time Calculator
Regenerative MRP replans every item. Net change replans only items affected by changes since the last run. This calculator estimates both durations so you can size a batch window or decide when each mode makes sense.
Your numbers
Total run time divided by items from a past run, multiplied by threads.
Changes ripple to components and parents, so more items are replanned than changed.
Your results
A linear model. Real runs also spend time on setup, database locking and writes, and speedup from parallel processes is rarely perfect. Calibrate with your own run logs.
Run time vs percent of items changed
Sweeps Items with changes since last run from 1 to 60, holding your other inputs fixed.
MRP run performance review
Optional: share run logs and we can point to where time is spent and which parameters to revisit.
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How to use it
Take the item count and runtime from a recent regenerative log, and work out the average time per item per process. Enter the percentage of items with changes since the last run, such as new demand, receipts or BOM edits, and a ripple factor for how many items each change touches. The calculator shows both run times and the saving.
- Use run logs, not vendor benchmarks.
- Estimate the ripple factor from a past net change run.
- Test the busy day case with a higher change percentage.
The method
Regenerative time equals items times processing time per item, divided by the number of parallel processes. Net change replaces the item count with the items actually replanned, which equals changed items times the ripple factor, capped at the full set. The crossover occurs when the changed share multiplied by the ripple reaches 100 percent, after which net change gives no advantage.
Reading the result
With 60,000 items, 45 ms per item and 4 processes, a full run takes about 11 minutes. At 8 percent change and a ripple of 2.5, net change replans 12,000 items in about 2 minutes. The chart shows both lines converging as changes grow. Use it to justify running net change during the day and a regenerative run weekly to clear drift.
Common mistakes
Teams run net change forever and never regenerate, which lets small data inconsistencies build up. Others assume linear speedup from more processes while the database becomes the bottleneck. Remember that terminology and options differ between ERPs, and some modern systems replan continuously, which changes the question entirely.
Frequently Asked Questions
When should I use regenerative MRP?
Run it periodically, often weekly or after mass data changes, to rebuild all planning results from scratch and clear accumulated inconsistencies. Net change handles the days between.
Why is net change not always faster?
A single change, such as an engineering change to a common component, can affect thousands of parents. When the ripple is large, net change approaches a full run.
Does adding processes always help?
Not linearly. Database locking, shared low level code and memory limits cap the speedup. Test increments and watch database wait times.
Is run time the right metric?
It is one of them. Also track exception volume, planner trust in the results, and how fresh the plan is when planners start their day.
If MRP windows are creeping into the working day, Netray can review run logs and planning parameters and suggest where run time is being spent.
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