Offset calculation

gaveup

I am currently having a bit of trouble determining if these wheels will fit and look good.

Currently I am on stock base wheels with 20mm spacers all around.

Stock:
18x8 +43 front
18x9 +15mm rear

With 20mm spacers it should be:
18x8 +23 front
18x9 -5mm rear

Right?

Wheels I am looking at are:

18x8.5 +25 front
18x10 +25 rear

According to the calculator I used
Front:
Inner clearance: 8mm LESS
Outer: EXTEND an extra 4mm

Rear
Inner clearance: 43mm LESS
Outer: RETRACT by 17mm

So just guessing, I would need to leave my 20mm spacer on in the back and it would increase to extend -3mm in the rear no?

Am I looking at this all wrong?

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2010 Magnetic Black Metallic 370Z 6M
stillen gen 3 CAI - topspeed test pipes - invidia gemini CBE - UpRev tune
301whp (HP Logic Mustang Dyno)