As a thumb rule, 1099 rate should be 10% more (1.1 times) the W2 rate assuming that you won't get any medical benefits or vacations on W2 also. With 1099, you will pay 7.5% extra on Social Security taxes. Also add 2.5% towards the employer's expenses to process your payrole,pay work man's compensation insurance etc. That's why employer reduces the 1099 rate by 10 to 11% if you get paid on W2.
For medical, deduct the hourly rate at the rate of $1.5 per person. If you have no kids, then deduct $3/hr (you and your wife). If you have 2 kids, then deduct $6/hr from your hourly rate (if the employer pays the full medical).
Some sample calculation for a 1099 rate of $60/hr
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1099 rate = $60/hr (no medical)
W2 rate = $54.5/hr (no medical)
W2 with full medicalbenefits for family of 3 = $50/hr (approx)
Annual Salary = 90K per Year. (Deduct 10K from W2 converted rate because of vacation, 401K etc).