Free travel for SA commuters after overcharging blunder

South Australian commuters will get a day of free travel on Friday, October 13, after an IT blunder saw hundreds of public transport users overcharged.

Tap-and-pay machines on the state's public buses didn't switch over to daylight saving time on Saturday night, meaning 650 passengers were incorrectly charged the peak hour rate between 9am and 10am this week.

Customers were charged up to $1.85 more than the usual rate on 750 buses across the state.

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A software update fixed the problem on 450 machines, with another 60 yet to be fixed.

The transport department was first made aware of the issue on Tuesday.

"There have been a number of machines that have had to be updated and that has had to be done through a manual process which has been quite labor intensive this is something that is unfortunate but the work is due to be completed this evening," Premier Peter Malinauskas said.

All public transport will be free on Friday as an apology to commuters, including trams, trains and buses.

Customers who were overcharged can contact Adelaide Metro for a refund.