IT contractors now cost the Commonwealth $1 billion a year, new data suggests.

The new figures show Federal Government outlay on IT contractors is on the rise, with some agencies having more than doubled their spending on external tech labour since 2014-15.

About a third of the Commonwealth's non-corporate and corporate agencies have disclosed their latest expenditure on IT contractors.

It appears that the 35 agencies spent just over $862 million on IT contractors in the 2018-19 financial year, up from $636 million in 2017-18 and $583.5 million in 2016-17.

But the new figures do not include spending at most Commonwealth agencies, including giants like Services Australia and the Australian Taxation Office. With those added in, the total is expected to be over $1 billion.

A detailed analysis is accessible here.