Medibank Private has apologised for a computer glitch that has affected payments for millions of its customers.

Medibank has hit some big hitches in the $150 million technology systems upgrade, and will not meet next week's deadline to get annual tax statements to customers.

“Even though it's still possible that we will have member's statements out by July 15, we wanted to be very transparent and front foot with our members, with our regulators, with the media and with our shareholders and say that we have got an issue, we're working on it absolutely around the clock,” Medibank's CEO Craig Drummond told reporters this week.

Medibank still has eight days to work out the issue, but it looks likely that customers will have to wait to file their tax returns.

“We are working around the clock to solve this issue and it's still possible that we may in fact meet that time,” Mr Drummond said.

“But we're not giving any timeframe... [because] the team is working absolutely around the clock to solve the problem rather than focusing on making promises that we may or may not be able to keep.”

Medibank is expected to undertake a full review of the computer system problems.