will definitely depend on combined income for the whole financial year, so depends on what time of year you have baby (if it's in July, your income will be negligible for the financial year so you'll get more - if it's born in May like my DD, your income will be much higher for that financial year - but from July 1 of following year, it will all change)

it's rather complicated, but as satya said, there is a calculator on the centrelink and FAO websites. if you go to centrelink.gov.au - on the left hand side there is a link to "online services" - and when on there, you can opt to run an estimator. if your partner has a good wage, you won't qualify for any income support payments (as they are for low income families) so just run a family assistance estimator