Ooops! Need to change that formula slightly. What I gave you will not work in January and reporting for December.
Leaving the current year alone and subtracting 12 from the month will adjust the year accordingly.
{table.date} in [dateserial(year(currentdate),month(currentdate)-12,1) to_ dateserial(year(currentdate),month(currentdate),1)]
Cheers,
WichitaKid