SamePeriodLastYear

I have been using the samperiodlast year function to calucation prior year revenues and counts of jobs and quotes. For some reason it has stopped working for me.

If I use this calculation then the number is the same as the current year no matter what I do. If change the date to be the job start date which I have linked to the calendar date table then it turns out blank. I am getting so frustrated and I have been doing these for a while and it is probably something small and stupid I am missing.

Total Est Rev PY = CALCULATE([Total Est Rev],SAMEPERIODLASTYEAR('Calendar'[Date]))