Gauge and sizing question

The instructions said 18 stitches to 4 inches, knitted loosely with DK on sz 7 needles. I don’t knit loose. I knit tight to normal. Make sense? A nice, even tension. I’ll go up a needle size and see what happens. Maybe a swatch this time! If I ever find a cardigan pattern that fits, I’m going to knit one in every color! I can’t get a cardigan to fit me for anything. I either misjudge my own body size or the pattern size. I always research the pattern on blogs to see if there are any sizing problems. Me thinks me thinks too much! Ya think?