i'm new here but i like pictures....so i use this one the most.
https://tiresize.com/wheel-offset-calculator/
it also allows me to compare current tire size / wheel / offset with what i am interested in putting on.
there is another one that shows suspension clearances and a side by side view (
https://www.wheel-size.com/calc/?wh...-65-18X9ET0&wcl=1.25in&fcl=2in&scl=2in&sr=0in), but i think they are estimating what a suspension / brake clearance is gonna be so i would be cautious on how much faith i put into it.
One important note is that each tire manufacturer may have a different actual size for the tire they produce verses the size used in the calculator (ie. Cooper STT Pro 285/65R18 according to cooper is 32.9 x 11.8 but the calculator will say a standard 285/65R18 is 32.6x11.2....just something to be mindful of) Hope the calculator with pics helps, it surely helped me get a good understanding of offset, now if i can master scrub, i'll be a guru...lol.