18 is on the bubble. 18+6=only 24, but 18+7=25. Responder will pass with 7. If you want to be safer, bid 2N with 18 and 3N with 19+.
Personally, I would rather play some 24-pt 3N contracts than play 2N with 25. I consider 25 HCP the 3N total, rather than Goren's 26 HCP.