There’s a few blogs out there which try to explain the problem and solutions. I looked at them and found that they were not always the easiest to wrap your head around. So, here is my solution which is hopefully a bit easier to understand and implement in your environment if needed.

**The Business Problem: **I want to calculate Month-over-Month (MoM) performance for online webinars

**Approach**: I know how many attendees attended webinars in a given month and therefore to work out the delta between Month 1 and Month 2 is simple subtraction. The problem is that the monthly attendee value is calculated by a COUNTROW function, surfaced by its own measure (Session Attendees). So, how do I keep this dynamic with the minimum amount of formulas?

**Solution**:

1. Create a new measure to show the Previous Month value:

**PreviousMonthMeasure = CALCULATE([SessionAttendeesMeasure],PARALLELPERIOD(SessionDate,-1,MONTH**

2. Create a measure to calculate the delta:

**MoMDeltaMeasure = SessionAttendeesMeasure – PreviousMonthMeasure**

3. To calculate the delta percentage, create a final measure

**MoMPerformanceMeasure = MoMDeltaMeasure/PreviousMonthMeasure**

(make sure you set this in the modeling as a percentage value)

In summary, your table should look something like this:

Month | Attendees
(SessionAttendeesMeasure) |
Previous Month
(PreviousMonthMeasure) |
Difference MoM
(MoMDeltaMeasure) |
Performance +/- MoM
(MoMPerformanceMeasure) |

July | 100 | 0 | 100 | 100% |

August | 150 | 100 | 50 | 50% |

September | 156 | 150 | 6 | 4 |