for Family Tax Benefit - the income estimate you provide is based on annual taxable income - for your self-employed partner, that would be his gross income minus allowable deductions.

If you are on parenting payment or another pension/allowance (not family tax benefit), to work out the fortnightly affecting income (most people will report their fortnightly gross earnings), Centrelink will generally use the figure from his last income tax return (they'll want to see the actual business/personal tax return, not the tax notice of assessment) unless there has been a change in circumstances (i.e. business generating higher or lower income than previous financial year) in which he would be required to complete a 3 monthly profit and loss statement (a 3 monthly projection forward) where the net (gross income minus allowable deductions) income is used until the next tax return is provided.

Once you know what your estimate is, plug it into the online calculator on the Centrelink website to work out your entitlement HTH.