Off-set wheels for Forester?

Can anyone tell me what my off-set is for a 98 Subaru Forester L with stock 15" wheels. I can't seem to figure it out. Printed on the wheel it reads (T 15x6 DOT 7 97 J6ER 4) Near the lugs it reads only (ER). I would like to put on custom wheels that have 10mm negative off-set to my current wheels so I can fit 20mm wider tires without the sidewall rubbing on the strut.

Stock offset is 45mm

alright thanks. I was hoping it was 50mm since most custom wheels are around 40mm. But that still leaves a couple 35mm wheels to decide on.

actually most wheel fitments that fit the WRX/imprezza should also fit your forester.