Is there a DAX calculation where i can decrease a value (price) by 30%. I am trying to work out the cost price of my products which is 30% less the item price?

I have tried:

Unit cost = sumx('sales', 'sales'[ItemAmount]* 0.70)

I would recommend to use a parameter, instead of a fixed percentage or value embedded in a formula. Parameters are more dynamic and allow some techniques that you may wish to use later in other scenarios.

Go to Modeling, New Parameter, a window pops up, complete the boxes. After clicking ok you will
see a new table â€śParameterâ€ť, a measure â€śParameterValueâ€ť and a slicer.

DAX formula example : [sum of sales] (1-ParameterValue) will do it.

You will find several videos that Sam created on this topic, keyword Scenarios Analysis.

Yes agree that use parameters here is a better and more dynamic way to run analysis like this.

Iâ€™ve created many videos around how to do this and also how to adjust values on a row by row basis.

To me youâ€™re close to getting what you need with SUMX, but if you want to only shock the price you need to add the price ( x 0.7 ) multiplied by the order quantity, not just have the itemamount only.

If would also help to see the actual results youâ€™re getting. This would assist in understanding behaviour of the measure a bit more.

Check out this video here which work through and example of how to complete this type of analysis.