I do gross.
I count everything as income, though. Gross income from employer, plus their contribution to my 401k, bank account interest, cash gifts (usually minimal, but a few k this year due to wedding gifts), tax refund from previous year (just because I don't want to adjust previous year), credit card points redeemed for cash, etc.
Then subtract every expense - all spending, taxes withheld, HSA disbursements, health insurance premiums withheld from each paycheck.
What's left is savings, and it had better match my cash savings, plus 401k contributions, plus HSA contributions minus HSA disbursements.
Then divide that by "income".
(every penny in - every penny out) / every penny in = savings rate