How to use multiple variables Stylus in calc()?

Just wrap the values into brackets, like this:

// *.styl

$gutter = 1rem

.sizeXS-m10
  width 'calc(%s / %s * %s - %s)' % (100% 12 10 $gutter)

She put me on the track:

// *.styl

$gutter = 1rem

.sizeXS-m10
  width 'calc(%s - %s)' % ((100% / 12 * 10) $gutter)