Communications Minister Malcolm Turnbull has accused the former Labor government of wasting up to $20 billion on the rollout of the National Broadband Network (NBN), but says the money lost could have been more than twice that amount.

The coalition on Thursday released a strategic review of the NBN, which found that under Labor's plans the rollout would miss its 2021 target by three years and cost $73 billion - up from $43 billion - to complete.

The coalition plans to deliver a fibre-to-the-node NBN, a slower but less expensive version of Labor's fibre-to-the-home plan.

Mr Turnbull said the NBN should have cost $15 billion to $20 billion "had you approached it the right way from the start".

"The cheapest way to complete this from where we are now, starting from the mess Labor's left us in, is $41 billion," he told Sky News on Sunday.