the formalla is :
remaining useful life = ( date of fixed asset that will be imported to SAP - starting depreciation date)\30 day.
and the result from this equation is subtracted from useful life of fixed asset.
note:
starting depreciation date =Dec 31 from the year that customer acqustion fixed asset.
example:
the capitalization date of an asset is 5/2/2012
I will consider starting depreciation date will be 31/12/2012
I will import the fixed asset on 1/1/2014
asset useful life is 80 Month.
then i will use the equation above to calculate remaining useful life
regards