Tax take almost $2b higher
The surplus for the 11 months to May was nearly $7 billion, up more than half on what was forecast.
The Treasury says the tax take is close to $2b above expectations, with increases in company, income and GST revenue.
It says it's expected that most of that increase will carry through to the full year accounts.
Government spending was relatively flat.
Net debt was better than expected at 19.3 percent of Gross Domestic Product, which is just below the government's self imposed target.
The surplus for the year ending June is expected to be just under $3.5b.