If you've tried to call Centrelink this year only to encounter a busy signal, you're definitely not alone.

In the first 10 months of this financial year, just over 42 million calls to the Government agency received an engaged signal, according to evidence presented to a Senate estimates hearing.

That compares to almost 29 million in the 2015-16 financial year, and 22 million the year before that.

Greens Senator Rachel Siewert said it shows the Centrelink system is "broken".

"This is an astronomical number representing Australians trying to access supports, adjust their payments, seek information or update their earnings," she told the ABC.

"That is a lot of frustrated people who may be exasperated and struggling."

The Department of Human Services said many people are still using mobile phone apps that allow them to redial "every couple of seconds" if they get an engaged signal.

Chief information officer Gary Sterrenberg said they were trying to work out how many people are constantly calling.

"The analysis we've asked our provider to do is to strip out those that try less than a number of times per segment of time, because obviously it's reasonable for them within a minute or two to try again, but it's actually not reasonable for them to try a thousand times a day, you know," he said.

Senator Siewert said she understood how that could be frustrating.

"But I can also see how people that are trying to get through to you would find that frustrating," she said.

The department's secretary, Kathryn Campbell, said they were "constantly looking" for ways to meet people's needs without them having to "try a thousand times".

Labor questions decision to contract 250 extra staff

The Government also intends to contract an extra 250 call centre staff to help manage the high number of calls.

But Labor senator Murray Watt questioned how much of a difference they would be able to make.

"Employing those 250 people, we work out, would require [them] to take 460 calls each day, every day of the year just to answer those missed calls," she said.

But Ms Campbell defended the approach, telling the committee the contract staff would be able to take some of the more simple calls.

"Hopefully if they were ringing — for example, 20 times a day — if we're able to take them on the first occasion, that would mean the other 19 calls wouldn't occur," she said.

Call wait times up to 38 minutes

Even if you manage to get through to Centrelink, you are still likely to face a wait before your call is answered.

The department also set out the average time callers have to wait across Centrelink's main phone lines.

For the financial year to the end of April they were: