baseline for freelance work is take your current (previous) salary and div by 1000 . 50K a year before? $50 an hour freelance.In reality you need more, but its a good "minimum" .
It actually may be more accurate to look at total comp: $50k a year + $12k in health benefits + $3k in equip + $4k in vacation + $1k in retirement benefits ~= $70/hr.
A per-day rate equivalent to $100..200 per hour is the cheap side of things. Don't cut yourself too short. Businesses have deeper pockets than most individuals.
It actually may be more accurate to look at total comp: $50k a year + $12k in health benefits + $3k in equip + $4k in vacation + $1k in retirement benefits ~= $70/hr.